Custom Buckling Spring Membranes

[wcass]

you might look into making custom membranes if folding doesn't work.

you can get the clear sheets in correct thickness from art/drafting supply (bottom is 5 mil, top is 3 mil). plan trace routing to new controller location and create a paper template. put the clear sheet on top of the template and trace the lines and dots with a conductive ink pen.

[mkawa]

samwisekoi and i have been talking about this, but the standard silver-based conductive pens (see: CAIG circuitwriter, mg chem equivalent, etc.) don't work very well on plastic. i don't understand enough materials/chem to know why, but i've found that it's only conductive over very short distances and has very high resistance even then. the bare conductive ink i just received is significantly better, but has very odd resistance characteristics that depend on geometry. in short, long skinny traces have ridiculously high resistance.

[hasu]

I had same experience with  circuit writer and shield paint for guitar cavity .  They are very brittle on curved surface once dried. cupper tape worked very well . Maybe 3m emboossed tape is the best . You can even solder on tape before apply on membrane .

Anyway, great progress!

[mkawa]

I had same experience with  circuit writer and shield paint for guitar cavity .  They are very brittle on curved surface once dried. cupper tape worked very well . Maybe 3m emboossed tape is the best . You can even solder on tape before apply on membrane .

Anyway, great progress!

what do you mean by cupper tape? can you elaborate? is it just that the silver inks need more texture to stick to the surface? thanks!

[regack]

I had same experience with  circuit writer and shield paint for guitar cavity .  They are very brittle on curved surface once dried. cupper tape worked very well . Maybe 3m emboossed tape is the best . You can even solder on tape before apply on membrane .

Anyway, great progress!

what do you mean by cupper tape? can you elaborate? is it just that the silver inks need more texture to stick to the surface? thanks!

Hah, this is funny, I didn't read it as cupper, I read it as copper tape... only after re-reading it did I see my brain automagically interpolated it for me...  Anyway, he probably meant Copper Tape.

[hasu]

I had same experience with  circuit writer and shield paint for guitar cavity .  They are very brittle on curved surface once dried. cupper tape worked very well . Maybe 3m emboossed tape is the best . You can even solder on tape before apply on membrane .

Anyway, great progress!

what do you mean by cupper tape? can you elaborate? is it just that the silver inks need more texture to stick to the surface? thanks!

Hah, this is funny, I didn't read it as cupper, I read it as copper tape... only after re-reading it did I see my brain automagically interpolated it for me...  Anyway, he probably meant Copper Tape.

Haha, Yes I meant copper tape. I wrote that on phone without dictionary
I used copper tape to fix membrane switch trace instead of conductive pen. At first I used normal not embossed copper tape but it was difficult to get conduction with trace. To make contact with trace I needed to needle tape. But 3M embossed copper tape(1245?) worked well without needling.

You can see some photos of my membrane sheet here. It is better than my English, hehe.
http://geekhack.org/index.php?topic=29483.0

[rknize]

Nice work, hasu.  Someone really determined could make reliable traces this way.

[mkawa]

I had same experience with  circuit writer and shield paint for guitar cavity .  They are very brittle on curved surface once dried. cupper tape worked very well . Maybe 3m emboossed tape is the best . You can even solder on tape before apply on membrane .

Anyway, great progress!

what do you mean by cupper tape? can you elaborate? is it just that the silver inks need more texture to stick to the surface? thanks!

Hah, this is funny, I didn't read it as cupper, I read it as copper tape... only after re-reading it did I see my brain automagically interpolated it for me...  Anyway, he probably meant Copper Tape.

Haha, Yes I meant copper tape. I wrote that on phone without dictionary
I used copper tape to fix membrane switch trace instead of conductive pen. At first I used normal not embossed copper tape but it was difficult to get conduction with trace. To make contact with trace I needed to needle tape. But 3M embossed copper tape(1245?) worked well without needling.

You can see some photos of my membrane sheet here. It is better than my English, hehe.
http://geekhack.org/index.php?topic=29483.0

i remember that thread! in fact, i've been looking for it forever! i've just de-archived it. would love more pictures of your membrane.

[The_Beast]

would love more pictures of your membrane.

I thought this was a family site?

\

[wcass]

if we are talking group buy already, how about getting a custom matrix made:
http://www.alibaba.com/product-gs/465289669/Flexible_Membrane_Circuit_Cables_with_Conductivity.html

instead of going from Unicomp controller to Teensy, you might go directly from membrane to a Teensy++. for connecting to the membrane, maybe an FFC like the older M's but with a right angle like this:
http://www.te.com/commerce/DocumentDelivery/DDEController?Action=srchrtrv&DocNm=520314&DocType=Customer+Drawing&DocLang=English
you could mount it behind the back plate, right at the top of the board and not need to bend or extend the membrane - just make a notch.

[mkawa]

wcass, if you can find a supplier that can do M sizes and the kind of complex artwork we need with reasonable MOQ and pricing i'm all ears. my understanding though is that small flex cables are a completely different animal from the large M membranes; the latter requires significantly more expensive tooling

[wcass]

wcass, if you can find a supplier that can do M sizes and the kind of complex artwork we need with reasonable MOQ and pricing i'm all ears. my understanding though is that small flex cables are a completely different animal from the large M membranes; the latter requires significantly more expensive tooling

i'll give it a shot. and you are right, small flex cables are very different than keyboard membranes. membranes are made using standard silkscreen technique only using conductive ink like DuPont 5021. the ink is sold by the KG, so need to find someone that is already doing this type of printing to make it cost effective. the membranes would be about 12"x5" - i can do the design, but will need a sample membrane in order to put the holes in the right place (all of my M's are of the 101 type).

[wcass]

do you think that the rivet positions are the same? either way, it might be good to have the measurements for all known models documented in the Wiki. i'll do the 101 membrane that i have and save as a PDF. if you print it out at 100% you could lay your membrane on top and see if the rivet holes line up. trace patterns will have to be changed of course, so i might leave them off for now.

[rknize]

The rivet positions between SSK and 101/4 are the same.  I used a new Unicomp mat on an SSK without any mods, other than cutting it down.

[mashby]

Thank you for splitting this from the original thread.

I'll track both, but I like that each topic has it's own thread.

[wcass]

would someone with a 104 membrane handy please check the contact points and rivet points on this drawing?
print it at 100% - best if you have legal paper - and lay your membrane on top. let me know what needs to move.

thanks

[mkawa]

The rivet positions between SSK and 101/4 are the same.  I used a new Unicomp mat on an SSK without any mods, other than cutting it down.

there's one rivet that appeared over the years and isn't present in early 90s era mats but is present in modern mats, but afaik this happened in both the SSK and the 101 key at the same time.

also it's not a huge compatibility issue. basically, include all the rivets from a 93ish M and you're good.

[wcass]

i submitted RFQ's to three membrane switch manufacturers requesting ...

I am trying to get replacement parts for a computer keyboard; very low volume. I do not need color, adhesive, embossing, domes, or connectors – I just need membranes with conductive print.

Material = polyester, DuPont 5021 or similar
Thickness = 0.075mm
Size = 300mm x 130mm
Print area = ~10%
Quantity = 5

i'll let you know if i get a bite.

On an unrelated note, i did a drawing of an idea i had for an M60 case. the basic idea was a milled upper and sides (aluminum or hardwood) and a sheet metal bottom. i was not planning on sharing it, but ...

• 5.74 inches is nothing to brag about.
• ribbed for her pleasure.
• as you can see, the testicles have not descended.

[mkawa]

i worry about the feel of the board with the backplate resting on a piece of aluminum, especially given that there will be protruding bolts (~1.5mm)

interesting idea though... hmmm......

[wcass]

 A reminder that this thread was split off from samwisekoi’s idea here. If this stuff looks interesting, please support his efforts to make a folded membrane and case for a 60% buckling spring keyboard.


The smaller the keyboard, the more important it is that it will accept multiple concurrent key-presses. NKRO is usually achieved in conductive keyboards by creating a one-way circuit using one diode per switch. But solderable flexible substrates are exotic and a diode anywhere near the switch might create enough of a bump to prevent the switch from working reliably. Can you tell that I have thought about this a lot?
I explained this idea in a few threads elsewhere; use a very thin PCB for the bottom membrane and route all of the traces to diodes beyond the border of the top membrane. As it so happens, there is an inexpensive surface mount diode available with specs similar to the common diode used with Cherry switches. But because they are 1x5 diode arrays, only 14 are needed for the M-60.
http://www.diodes.com/datasheets/ds31437.pdf

I already have very thin flexible blank PCB – enough to do 6 of these boards. It is 8mil thick – only .003” thicker than the original IBM bottom membrane. I have the skill and tools to DIY etch these boards, but don’t have the skill or tools to mount the diodes. If anyone has reflow experience out there, I would be happy to supply the parts to make several and ask for a subset back. If I don't get any volunteers then i will likely build a prototype without the diodes and check into the cost of having the the boards etched and assembled by Sitopway Technology or other vendor.

http://www.skycraftsurplus.com/coppercladboard23x17x00080.aspx

I have a very simple design for the bottom membrane that is similar to the original IBM design. I figured that “single-sided” would create less stress on the traces when clamped to the curved back plate. The controller would be made from a Teensy++ (no pins) with two FFC connectors mounted on it. The controller would end up top-center under the back plate. I’ve included some drawings below and will work on more for anyone having trouble visualizing it.
 M60_bottom.pdf
As I said in my previous post, I send out 3 RFQ for a custom top membrane to companies that advertise they will do jobs as small as one piece – and today one of the vendors contacted me asking for a drawing in order to make an estimate.
The final piece of the puzzle is programming the Teensy++. I would really like to leave that to someone better qualified. I hope to be able to offer assembled parts as a bribe.

[mkawa]

can you just send them your M60 drawing and see what they say? that's a nice, non-trivial starting point.

[wcass]

membrane vendor #1 update:

Dear William,
Thank you for your fast letter.
We have checked your PDF file , we can produce it for you .
For 5pcs, the mold fee is USD$100,  plus sample fee USD$120, total will need USD$220, and you will need to pay for the shipping.
If interest , pls feel free to contact us ,thank you .
Best regards,
Amy

 
i am sure that it is like PCB orders and cost would scale down significantly as quantity increases, but $44 a membrane is not what i was looking for.
 
i have yet to hear from the other two vendors and i think i will also ask local print shops to see if they have done (or would like to do) screen printing with electricly conductive inks. i am going to get a sheet of 3mil poly from a local art supply and bake it for a couple minutes at 90C to simulate curing process and see how it holds up.
 
mkawa, IIRC you said that you have tried the carbon ink and that resistance increases with the length of the trace. i think that resistance would be too high with that alone - but what do you think about using carbon ink for the contact points only and running magnet wire from dot to dot?

[mkawa]

here's the datasheet for the carbon ink: http://bareconductive.com/file/technicaldatasheet-bareconductivepaint-pdf

the short answer is yes, the resistance goes up with the length of the trace. a 1.5in" trace made by pen was about 1.2ko. the longer answer is that big traces can be low-resistance, but the ratio of length to height must be small. it's weird and counterintuitive.

eta: i have thought about magnet wire. you don't even need the carbon ink to affix the magnet wire at each point: tape works fine. the problem is basically that it's a pita to produce sheets like this in any kind of volume at all.

[hasu]

I came across this interesting stuff today. Snaptron domes. http://www.snaptron.com/
I wonder this dome switches with thin flex PCB works well instead of membrane sheets. Their actuation force is beyond 200g, I'm not sure model M hammer can push down these domes.

[wcass]

i do not think that metal dome switch would work any better. the base PCB has two contact points per switch - rim and center. the metal dome sits on the rim contact and over the center contact. pressing hard enough on the dome will deform it to complete the circuit.
 
what might work better is if we could make the hammers conductive and place one contact point at the hammer "pivot" and another where the hammer "head" strikes the board. there could be no padding so it would likely be noisier than an F.
http://www.thomasnet.com/articles/custom-manufacturing-fabricating/how-to-metalize-plastic
 
i should have a test PCB and membrane done in the next ten days or so. the barrel frame i have is cracked from age. i will try to repair it with epoxy unless someone has a spare barrel frame that they would like to donate to this experiment.
 
hasu, i acknowledge your programming skills. could i ask your help with a test controller? i have a Teensy++ and the matrix will be 15 columns by 5 rows. the rows would be on the cathode side of the diodes. you can pick the pins.

[rknize]

Model cement works better, as described here:

http://wiki.geekhack.org/index.php?title=Modifications:IBM_Model_M:Cracked_Barrel_Frame_Repair

Alternatively, they are available from Unicomp in both full and SSK sizes for $10.

I've thought about the conductive hammer idea before.  There are several problems with it, but they are not insurmountable.  Any conductive coating or paint would be prone to wear where it matters the most: at the hinges and the contact point.  A better solution might be a very light spring made from a "U" of fine piano wire or similar.  This would be a lot of manual labor, though, and does not scale well.  Another idea I had was a piece of copper or aluminum tape on the hammer with a fine wire "brush" to bridge to the moving hammer.  Again, this is a lot of manual labor and there may be key bounce issues with such a setup.

[hasu]

OK. I'll try to code for this project this weekend.

i should have a test PCB and membrane done in the next ten days or so. the barrel frame i have is cracked from age. i will try to repair it with epoxy unless someone has a spare barrel frame that they would like to donate to this experiment.
 
hasu, i acknowledge your programming skills. could i ask your help with a test controller? i have a Teensy++ and the matrix will be 15 columns by 5 rows. the rows would be on the cathode side of the diodes. you can pick the pins.

[Hubbert]

I encourage the conductive hammer approach.

[mkawa]

cracked barrel frames are no fun. unicomp can have a new one for you lickety split

[hasu]

wcass, can you post your matrix schematic or top and bottom sheet pics?
It is needed to define keymap of your firmware.

I found bottom pcb pic above but it has only 14 lines, not 15. I guess it is not final design.

OK. I'll try to code for this project this weekend.

i should have a test PCB and membrane done in the next ten days or so. the barrel frame i have is cracked from age. i will try to repair it with epoxy unless someone has a spare barrel frame that they would like to donate to this experiment.
 
hasu, i acknowledge your programming skills. could i ask your help with a test controller? i have a Teensy++ and the matrix will be 15 columns by 5 rows. the rows would be on the cathode side of the diodes. you can pick the pins.

[wcass]

i will be making the top sheet from 3mil poly and copper tape (thanks for that too!). 5 tape lines strait across the sheet - one for each row.

attached is what i will be etching this weekend. i dropped a block on top of where the 14 diodes will go to complete the circuit. if this works as well as i think it will then i will contact a couple PCB assembly shops to see what it would cost to get them etched and assembled for us with diodes in place. as it is an etch - it is a mirror of what will be on the PCB.  PCB3.pdf (22.71 kB - downloaded 384 times.)


actually, better swap the Baskspace for the Del because the diodes will not be in on this test board.

[hasu]

OK. Try this and let me know your result.
https://github.com/tmk/tmk_keyboard/tree/mm60
https://github.com/tmk/tmk_keyboard/archive/mm60.zip

Pin usage is PD0-PD7 and PC0-PC5 for column PB0-4 for row.
It doesn't support ghost-block feature at this time, so you may experience ghost key with some key combinations. Though I don't think this is a big problem for testing purpose.

I named this project mm60 tentatively, but fell free to rename it.

[wcass]

THANK YOU HASU!

i am no expert at this, but here are my notes and some pictures from etching.

previous experience has taught me that my home printer does not work for this. if you are thinking of doing DIY PCB fabrication and you do not have a high-end laser printer, save your drawing to PDF and take it to your local office supply for printing on "glossy" paper. this paper is available in 11x17 and is almost as good as specialty transfer paper. it is also going to be "in stock" and the cost is next to nothing - just 32 cents with my drawing on it. use the in-store paper cutter to trim to size.

the paper at my local Office Depot tends to shrink about 1% when heated, so i scaled my drawing to 101%. just before ironing, i heat my drawing in the oven at 200F for about 5 minutes to pre-shrink the paper before putting it on the copper. i know that i have ironed enough when the drawing has bled through to the top (about 10 minutes for a board this size) and then drop it in a water bath for about 10 minutes. as you peal the paper off, there should be little ink left on the paper (most should be on the board).



i soaked and etched in a drawer from a cheap storage bin. i gave it a too-quick inspection before i etched. looking at the pictures and knowing where they are, i can now easily spot two breaks. the third break can't be seen without significant magnification.

[mkawa]

these breaks should be easy to fix with a conductive pen (eg, caig circuitwriter). good job man!

[wcass]

another weekend and more progress.

i cut the back plate today. here are a few pictures of the back plate, a test bottom "membrane", and controller.

what's that? you say you can't see the controller? here's a picture of it from the rear edge.

still don't see it? OK, i'll flip it over.


the connector is a right angle 17 pin FFC connector that i got from Digikey. i will only be using 15 pins; PD0-PD7, PE0-PE1<not connected>, PC0-PC6. i might move it over a tenth of an inch to improve access to the mount hole under the USB connector or decide to flip the controller to the top, depending on how it fits in a case.

speaking of keyboard case, has anyone tried anything like this? suggestions/constructive criticism would be appreciated.
http://geekhack.org/index.php?topic=40006.msg816503#msg816503

[mkawa]

have you seen the prototype picture i posted in the ssk thread? we've had some ideas a bit like that, but without the top bit and using 3d printed material as the substrate

[wcass]

have you seen the prototype picture i posted in the ssk thread? we've had some ideas a bit like that, but without the top bit and using 3d printed material as the substrate

i have been following your thread and samwisekoi's as well, but had not see your new picture yet; thanks.

your comment about torque causing a failure - makes me think that my bottom, should have upturned sides and be 1.5mm or more thick.

[mkawa]

how are you planning on securing the pcb to the plate? bolts?

[wcass]

yes, a standard bolt mod. the PCB is only 8mil - the orginal bottom membrane was 5 mil, so i don't forsee any issue.
the top-most and bottom-most rows will secure the keys/frame/membrane/plate assembly to the case bottom (or top - depending on case design).

[mkawa]

nut torque will depend on what frame you use i think more than the plate. post some pictures before you throw the barrels on and i'll eye it

[wcass]

ooooooooohhhhh - you were talking nut torque! i thought you were talking case torque (4 corners of the case not on the same plane).
 
i've done a few bolt mods, so i don't expect that to be a problem.

[wcass]

more pictures.

this is a practice pcb with a sheet of clear 3mil plastic on top and i am cutting the mount holes. keeping the sheet and pcb aligned was a pain in the butt. in the end i used double-sided tape.


i started with 5mm copper tape that comes with paper backing. it is a pain to work with because it has the worst properties of wire and tape; it sticks to itself, bends, and kinks. as you can see i cut several of the traces too short and had a very hard time taping in a strait line.


it will be interesting to see how much of a difference the misaligned traces make to the keys registering. i'm waiting now for a barrel frame and a few key caps from Unicomp.

[wcass]

OK. Try this and let me know your result.
https://github.com/tmk/tmk_keyboard/tree/mm60
https://github.com/tmk/tmk_keyboard/archive/mm60.zip

Pin usage is PD0-PD7 and PC0-PC5 for column PB0-4 for row.
It doesn't support ghost-block feature at this time, so you may experience ghost key with some key combinations. Though I don't think this is a big problem for testing purpose.

I named this project mm60 tentatively, but fell free to rename it.

so i read the readme.md from the first link and downloaded and expanded the second link.
i installed WinAVR, opened a command prompt from the ...\tmk_keyboard-mm60\keyboard\mm60 folder ran make -f makefile.pjrc
it created some files and folders and spat out a bunch of of text including ...

Code: [Select]

Creating load file for Flash: mm60_pjrc.hex
avr-objcopy -O ihex -R .eeprom -R .fuse -R .lock -R .signature mm60_pjrc.elf mm6
0_pjrc.hex

Creating load file for EEPROM: mm60_pjrc.eep
avr-objcopy -j .eeprom --set-section-flags=.eeprom="alloc,load" \
        --change-section-lma .eeprom=0 --no-change-warnings -O ihex mm60_pjrc.el
f mm60_pjrc.eep || exit 0

Creating Extended Listing: mm60_pjrc.lss
avr-objdump -h -S -z mm60_pjrc.elf > mm60_pjrc.lss

Creating Symbol Table: mm60_pjrc.sym
avr-nm -n mm60_pjrc.elf > mm60_pjrc.sym

Size after:
   text    data     bss     dec     hex filename
  20156      24     153   20333    4f6d mm60_pjrc.elf

-------- end --------

i presume that now i need to use the teensy loader to load the created hex file. is that correct? do i need the other files and folders for anything?

[hasu]

You are right. You need only hex file to program your controller.

[wcass]

ok, the hex file is loaded and the OS picks up the device, but is the matrix completely blank? i have shorted various row/columns and no keystrokes are registered? how do i test functionality?

[hasu]

Short B0 and D1 with wire or something and see if you get '1' on computer.

EDIT: Added code to enable debug print. Get new source from 'mm60' branch of github and see debug output with 'hid_listen'.

[wcass]

hid_listen replies for the first short only - shorts after this do not display anything. also second keyboard and mouse clicks do not register properly until the computer is rebooted. i duplicated the keyboard issue with USB and PS2 keyboards.  also, when the teensy is plugged in, the LED on the teensy has a dim glow.
the hid_listen reply is ...

r23 +07 rF0 r23 -07

i do not solder well, but i did test with a multimeter before programming and it checked out with no shorts. here is a picture of my ugly solder results.

[hasu]

Matrix read code didn't work. Fixed now. Try new code. Tested and confirmed that left part of matrix works on ATMega32U4, but I have no Teensy++ in hand now to test full matrix.

hid_listen can only work with first Teensy, second one is ignored. Disconnect another Teensy to debug.

[wcass]

i still can't get it to work. it is not locking up the other keyboard, but it is not being seen by hid_listen. windows device manager adds a human interface device when i plug it in, but does not add a keyboard device. hid_listen says "waiting for device . . . . . " and keeps waiting as i short rows and columns.

[hasu]

Wierd. I think you should get some debug output when you short any column and row pin.
Are you sure about using latest source?

[wcass]

date and time are march 17 4:44 pm

[hasu]

can you use git command? if so try 'git log'. if not get zip archive again.

EDIT: BTW, you should get debug output like this.

Code: [Select]

Device disconnected.
Waiting for new device:.........
Listening:

r/c 0123456789ABCDEF
00: 0001000000000000
01: 0000000000000000
02: 0000000000000000
03: 0000000000000000
04: 0000000000000000

---- action_exec: start -----
EVENT: 0003d(22163)
ACTION: ACT_LMODS[0:20]
keys: 20 00 00 00 00 00  mods: 00
processed: 0003d(22163):0

33333333333333333333333333333333333333333333333333
r/c 0123456789ABCDEF
00: 0000000000000000
01: 0000000000000000
02: 0000000000000000
03: 0000000000000000
04: 0000000000000000

---- action_exec: start -----
3EVENT: 0003u(24787)
ACTION: ACT_LMODS[0:20]
keys: 00 00 00 00 00 00  mods: 00
processed: 0003u(24787):0


[wcass]

i am not familiar with git tools. i re-downloaded and re-compiled. fc /b oldfile newfile found no difference. so i tried it on a second teensy and hid_listen still does not pick up the device.

it probably would help if you had a teensy, so please PM me with your address and i will send you one of mine.

[mkawa]

i'm happy to send a full suite of teensies to hasu. let me know before you ship out to him wcass

[hasu]

Thank you for offering. If you can donate a spare Teensy it is very helpful to me.
Actually I have one Teensy++ 2.0 as controller of my HHKB now, which is one of my daily driver boards. I must unscrew to open enclosure and get access to Teensy++, this is exactly what I'm doing now and it is PITA a bit.

OK. I forgot Teensy has LED on port PD6, we can't use this port as column line to sense matrix.
I updated repository to disable PD6, try it again. I believe you can see some on hid_listen now,
though you can't get 7,y,h,... column keys atm.

[mkawa]

wcass, can you pm me? i can forward your extra teensy on to hasu with the rest of the varieties and whatever else he wants from the states

[wcass]

success! it registered keystrokes!

the barrel frame is in the mail, so i am just tapping my fingers lightly on the top of the membrane. i am now very confidant that this will work. it does not seem to matter that the top traces are a bit lot crooked.

hasu, i am planning to etch a new PCB. will we be able to use PD6? the 17 pin FFC connects to all pins from PD0 to PC6 - i need 15 of these for columns. could we use PE0 or PE1? also, i flipped the teensy over so it is now on top of the matrix. it receives the row wires better that way and should be easier to mount the switch assembly to a case bottom. i know that changes the matrix row and column order - left-most column is now PC6 and right-most column is at PD0; top row is PB4 and bottom row is PB0.

[hasu]

PD6 might be able to used with some extra trick but I'm not sure. You'd better not to use PD6. Yes, you can use PE0 and  PE1, instead.
How do you want to use pins for column lines actually? PC6 for left most and PD1 for right most lines and PD0 is not used?

[wcass]

PD6 might be able to used with some extra trick but I'm not sure. You'd better not to use PD6. Yes, you can use PE0 and  PE1, instead.
How do you want to use pins for column lines actually? PC6 for left most and PD1 for right most lines and PD0 is not used?

you can pick the pins - any 15 of that 17 will do.

[hasu]

OK. I changed matrix code. Pin usage is indicated below. Column 15 doesn't exist, so D0 is not used.

Code: [Select]

* col: 0   1   2   3   4   5   6   7   8   9   10  11  12  13  14  15
* pin: C6  C5  C4  C3  C2  C1  C0  E1  E0  D7  D5  D4  D3  D2  D1  D0

* row: 0   1   2   3   4
* pin: B4  B3  B2  B1  B0

EDIT: Update code again. Try latest code if you have a problem.

[wcass]

so i am getting to the point where i need to hold the key assembly to actually test typing. what i have come up with seems to be very stable even without sides or the back edge attached.

to attach the back i will need a 2mm tap to thread the 22 gauge sheet metal. for a production run, the metal work would be done by an expert; the angles would be less curvy and screw heads countersunk at bottom front.

[sleepy916]

Looks like things are moving along nicely, great work so far!

[mkawa]

nice! some neoprene might compensate for bolt thickness on the bottom of the plate when you get there

note: i don't think you're going to be able to countersink screws in there. it's really thin mild steel

[AKIMbO]

Sweet......looking good wcass!

[bazemk1979]

wcass your wizard men!!!!!!!!!!!!!!!! Making case for this would be very hard. Maeby its cheaper to make plastic case instead of aluminum?

[wcass]

wcass your wizard men!!!!!!!!!!!!!!!! Making case for this would be very hard. Maeby its cheaper to make plastic case instead of aluminum?

i'm hoping that i can design a case that is attractive, solid, and affordable; worthy of this keyboard's heritage. the cost for the raw material for my case is less than $10, but to make it pretty will likely cost 4 or 10 times that for labor depending on quantity. i think that cost per keyboard would be under $100 if quantity is > 500, but i don't predict that kind of interest. buckling spring is a niche market; 60% boards are a niche; people willing to spend $100 on a keyboard is a niche.

the best case scenario that i can think of is this:
i get it working and it is beautiful. i send it over to Unicomp for them to take a look at it. i talk them into agreeing to assemble and sell the keyboard IF i can guarantee some quantity will sell. Kickstart.

[bazemk1979]

that can be a start too, but don't  forget my brother, you might not find 500 that will go for the BS mini, you might be surprised if turns out they are around 300 interested in it..... Everybody here loves the small factor.

[wcass]

another weekend and more progress.

i re-did the top membrane trying for straighter lines. i also cut some grooves in the barrel frame for the wires to run up to the top.

much better, but won't work - look at the left side with the separator sheet in.


let's ignore that for a while and go to the other side where the wires come into the teensy. it is inconvenient having the wires soldered directly to the membrane and teensy so i thought i would use standard pins and sockets. i have strait pins already, so i soldered on 7; five for the rows and two for caps lock and num lock LEDs. but it looks like there is not enough clearance for the strait pins and socket. i'm accepting suggestions for another connection method. i also mounted a ground wire and USB socket on the rear of the case.


Going back to the OP, i have been researching other methods for creating custom membranes and i think these two look promising. please comment back which one you think i should try.

inkjetFlex.com is a contract manufacturing company out of the UK that will do prototypes pretty inexpensively. the minimum order is 300mm x 300mm (enough for two membranes) for £25. but the prototype service allows no choice for substrate - 4mil PET (Unicomp uses PE - 3mil for top and 5mil for bottom) and added price of shipping would put the cost per sheet at about $30.
http://inkjetflex.com/site/rapid-prototyping/

the other promising method is true DIY for now, but a commercial version might be right around the corner. early last year, researchers at the University of Illinois developed an ionic silver solution "ink" that evaporates leaving behind pure solid silver bonded to the substrate. the solution contains just 3 easily sourced chemicals - none of which react with plastics. i found an odd DIY write-up here: http://jordanbunker.com/archives/41  i would probably do the same thing but would also get some empty refillable marker pens for easy dispensing. that and some quality mask like FrogTape.

[mkawa]

the problem with the diy ink is two-fold i think. first of all, it doesn't come with a method of automated printing, and i imagine that shoving a syringe full into a 30$ inkjet printer will not end up happyfunland. second, i am not to be trusted with dangerous chemicals, period.

inkjetflex.com looks the most promising, but the pricing is not attractive at all. that said, the prototyping pricing isn't insane; it's actually pretty reasonable. the real problem is that there's no way of upping the volume once we feel good about a prototype... :/

basically, we can get like 4-10 copies printed for high but not impossible prototyping pricing with short lead time OR we can get 1000 made for true volume pricing. there's just nothing inbetween.

oh, AND to ***** even more, we still can't get the reall cool stuff we want with either of these options: capacitive sensors or on-fcb diodes. BLARGH

[wcass]

As I said before, the best case scenario is that Unicomp likes the idea and agrees to assemble and sell the keyboard. They would probably want a guarantee that some quantity will be purchased (this is where a Kickstart campaign would help). And this keyboard will be NKRO when in production. The diodes will go on the bottom PCB.

I think I have created enough prototypes to have worked out most of the early design flaws. I need to get quotes for factory produced PCBs and sheet metal work. If there is interest I will organize a small group buy.


My DIY membrane is only semi-functional. There is still interference where the copper tape is deformed or rippled. I did create a CAD file for a professionally made membrane that will curve around and slides into another FFC connector on the top of the Teensy. One of the pins that I have been using for rows (PB4) is blocked by the Teensy's USB connector, but it looks like PF0-PF4 might work.

[wcass]

i just bought a bunch of Pyralux, so i will be making my top sheet the same way as i make the bottom sheet; DIY etching.
http://www.ebay.com/itm/190815165931

[wcass]

I have asked Hasu to make a few changes to the code - hopefully the last.

• enable Caps Lock on PB6 and Num Lock on PB5
• move rows to PF0 - PF4
• other small changes to column pin and key assignments (detailed below)

I had to add a dedicated Delete key because this prototype does not have diodes (the next prototype will!), so Ctrl+Alt+(Fn+Backspace) would generate a "ghost S". Adding the delete meant that some key had to go and I chose the tilde/grave. I would like to still be able to produce these characters and the obvious choice is Fn+Esc - but how would i do a tilde without getting a caps lock? So maybe we need a macro (Shift+grave) and assign that to Fn+backslash.

We also need a Num Lock key (Fn+N) and a few changes to the Num Lock layer to match the key caps. The num lock layer is primarily for typing escape characters which requires using the keys on the num pad. 

[hasu]

OK. I need to know some.

1. Which pin of LED do you connect with those ports? Anode or Cathode?
2. No problem.
3. You flip column pins again?

Note that
A. 'NumLock' LED is controlled by host, it doesn't indicate state of Num Lock layer.
B. 'NumLock' key(NLCK) just register numlock scancode to host, not activate 'Num Lock Layer'. You need Fn key on 'Function Layer' to switch that layer.
You probably need two separate keys; normal 'NumLock' key to control numpad state of host and Fn key to activate 'Num Lock Layer' respectively.

I think this is close to what you want. You can toggle Numpad layer with Fn+N(FN2+FN1) and 'N' key works as Numlock key on Numpad layer(Layer1).

Code: [Select]

static const uint8_t PROGMEM keymaps[][MATRIX_ROWS][MATRIX_COLS] = {
    /* Layer 0: Default Layer
     * ,-----------------------------------------------------------.
     * |Esc|  1|  2|  3|  4|  5|  6|  7|  8|  9|  0|  -|  =|  \|Del|
     * |-----------------------------------------------------------|
     * |Tab  |  Q|  W|  E|  R|  T|  Y|  U|  I|  O|  P|  [|  ]|Backs|
     * |-----------------------------------------------------------|
     * |Fn2   |  A|  S|  D|  F|  G|  H|  J|  K|  L|  ;|  '|Return  |
     * |-----------------------------------------------------------|
     * |Shift   |  Z|  X|  C|  V|  B|  N|  M|  ,|  .|  /|Up |Shift |
     * |-----------------------------------------------------------|
     * |Ctrl|Gui |Alt |      Space             |Alt |Left|Down|Righ|
     * `-----------------------------------------------------------'
     */
    KEYMAP_ANSI(
        ESC, 1,   2,   3,   4,   5,   6,   7,   8,   9,   0,   MINS,EQL, BSLS,DEL, \
        TAB, Q,   W,   E,   R,   T,   Y,   U,   I,   O,   P,   LBRC,RBRC,BSPC, \
        FN2, A,   S,   D,   F,   G,   H,   J,   K,   L,   SCLN,QUOT,     ENT,  \
        LSFT,Z,   X,   C,   V,   B,   N,   M,   COMM,DOT, SLSH,     UP,  RSFT, \
        LCTL,LGUI,LALT,          SPC,                     MENU,LEFT,DOWN,RGHT),

    /* Layer 1: Numpad
     * ,-----------------------------------------------------------.
     * |   |   |   |   |   |   |   |  7|  8|  9|   |   |   |   |   |
     * |-----------------------------------------------------------|
     * |     |   |   |   |   |   |   |  4|  5|  6|   |   |   |     |
     * |-----------------------------------------------------------|
     * |      |   |   |   |   |   |   |  1|  2|  3|  *|   |        |
     * |-----------------------------------------------------------|
     * |        |   |   |   |   |   |   |Nlk|  0|  .|  /|   |      |
     * |-----------------------------------------------------------|
     * |    |    |    |                        |    |    |    |    |
     * `-----------------------------------------------------------'
     */
    KEYMAP_ANSI(
        TRNS,TRNS,TRNS,TRNS,TRNS,TRNS,TRNS,P7,  P8,  P9,  TRNS,PMNS,PPLS,TRNS,TRNS, \
        TRNS,TRNS,TRNS,TRNS,TRNS,TRNS,TRNS,P4,  P5,  P6,  TRNS,TRNS,TRNS,TRNS, \
        TRNS,TRNS,TRNS,TRNS,TRNS,TRNS,TRNS,P1,  P2,  P3,  PAST,TRNS,     PENT, \
        TRNS,TRNS,TRNS,TRNS,TRNS,TRNS,TRNS,NLCK,P0,  PDOT,PSLS,     TRNS,TRNS, \
        TRNS,TRNS,TRNS,          TRNS,                    TRNS,TRNS,TRNS,TRNS),

    /* Layer 2: Function
     * ,-----------------------------------------------------------.
     * |  `| F1| F2| F3| F4| F5| F6| F7| F8| F9|F10|F11|F12|  ~|Ins|
     * |-----------------------------------------------------------|
     * |     |   |   |   |   |   |   |   |   |   |Psc|Pus|   |Delet|
     * |-----------------------------------------------------------|
     * |      |   |   |   |   |   |   |   |   |   |   |   |        |
     * |-----------------------------------------------------------|
     * |Caps Loc|   |   |   |   |   |   |Fn1|   |   |   |PgU|Caps L|
     * |-----------------------------------------------------------|
     * |    |    |    |                        |    |Home|PgDn|End |
     * `-----------------------------------------------------------'
     */
    KEYMAP_ANSI(
        GRV, F1,  F2,  F3,  F4,  F5,  F6,  F7,  F8,  F9,  F10, F11, F12, FN0, INS, \
        TRNS,TRNS,TRNS,TRNS,TRNS,TRNS,TRNS,TRNS,TRNS,TRNS,PSCR,PAUS,TRNS,DEL,  \
        TRNS,TRNS,TRNS,TRNS,TRNS,TRNS,TRNS,TRNS,TRNS,TRNS,TRNS,TRNS,     TRNS, \
        CAPS,TRNS,TRNS,TRNS,TRNS,TRNS,TRNS,FN1, TRNS,TRNS,TRNS,     PGUP,CAPS, \
        TRNS,TRNS,TRNS,          TRNS,                    TRNS,HOME,PGDN,END),
};

static const uint16_t PROGMEM fn_actions[] = {
    [0] = ACTION_LMOD_KEY(KC_LSFT, KC_GRV),
    [1] = ACTION_LAYER_BIT_TOGGLE(1),
    [2] = ACTION_LAYER_BIT_MOMENTARY(2),
};


[wcass]

1. Which pin of LED do you connect with those ports? Anode or Cathode?
2. No problem.
3. You flip column pins again?

1) the backplate is ground and the pin next to these two is +5, so eather will be easy for me, just let me know. pulling the pins low might be the most elegant wiring.
3) yep, re-design of top membrane.

Thanks

[hasu]

Updated the code. Try it on your new keyboard.
LEDs should be connected to Teensy with cathode and to 5V with anode. Also try the keymap and let me know if it differ from what you want.
You can see the change here.
https://github.com/tmk/tmk_keyboard/commit/ec1c321fb144f7991ab0e0add48b841cc3cccf85

BTW, I didn't know Paralux at all and it looks like an interesting material. It is nice to know.

[wcass]

copper clad polyimide (Paralux is a brand name) should work better than any of the other DIY solutions. i have considered it in the past, but it always seemed too expensive for prototypes. but after getting quotes for conductive silkscreening and printed copper i decided to check out eBay again and found this vendor. $45 (with shipping) but enough material for 12 boards - $3.75 a board is very nice! You do have to etch it yourself, but that only adds about $2 material and an hour of time.
 
Mouser is delivering the FFC connectors on monday and the Paralux should arrive about the same time.

[mkawa]

i just bought a bunch of Pyralux, so i will be making my top sheet the same way as i make the bottom sheet; DIY etching.
http://www.ebay.com/itm/190815165931

not bad actually. cheaper than inkjetflex.com.. does the seller have a steady supply of sheets?

[wcass]

it looks like the seller is a liquidator - but he has a lot of this on hand. he is selling 6 more batches of (4)12"x18" and 8 lots of (50)12"x18"

[mkawa]

is it 30 per 4 sheets or 30 per sheet?

pyralux would allow both capacitive sensing and potentially even diodes.. it's also technically printable (but i'm not sure how scalable the printing process is..)

quite interested to see how this goes for you wcass. it may not be a magic bullet but it's definitely an option worth exploring

[wcass]

is it 30 per 4 sheets or 30 per sheet?

pyralux would allow both capacitive sensing and potentially even diodes.. it's also technically printable (but i'm not sure how scalable the printing process is..)

quite interested to see how this goes for you wcass. it may not be a magic bullet but it's definitely an option worth exploring

"$30 for 4 sheets" is the way i read the ad. i'll let you know when i get it. these sheets are single-sided, double sided or thin PCB (like the 8mil stuff i got for my bottom membrane) would probably be better for capacitive; the problem there is finding controller.

diodes is possible, but you probably want to put those on the bottom membrane (because it moves less) and keep them away from the actual switch area. this is exactly what i have planned.

[mkawa]

no, there's space on top of the pcb under the frame sills. there actually isn't space under the pcb, because that's flush with the backplate. also you'd need vias to route traces on the bottom of the pcb. yuck

[wcass]

no, you misunderstand.

the "membrane set" is made up of 3 sheets - the sheet closest to the backplate is the "bottom sheet". this sheet is least effected by vibrations from hammer strikes. i have my "bottom sheet" made from 8mil PCB. diodes will go on the top side of this sheet near the back of the keyboard at the end of each key column. that way the slight bump from the diode does not create a ripple for the "middle sheet" (just holes) or the top sheet.

[mkawa]

oh, i was thinking that if we have pyralux, ie, a material strong enough to actually survive repeated light contact with the hammer, we might as well do a capacitive switch, in which case we only need one fcb layer..

[wcass]

oh, i tried that first. back during the "great GH outage of 2012" i posted here:
http://deskthority.net/workshop-f7/bringing-the-ibm-pc-xt-into-the-21st-century-t3047.html
 
i managed to completely duplicate the capacitive pads of a model F and cut a new barrel frame that put the keys into a modern tenkeyless configuration - all this fitting back inside an XT case, but was not able to get a controller to work. the last post of that thread i discuss the idea that i am working on here.

[mkawa]

ah. either one's a possibility, and you are right in that the membrane style will be the easiest to try first (although i worry about the pyralux's resilience..)

in the meantime, we're still waiting to see how many sheets you get for your 30$

[wcass]

 I’m not sure I mentioned this before, but I suck at soldering. I was using a “helping hands” and did this to my Teensy. It no longer works, so I have sent for a new one.

But I am not about to stop just because I suck at something. I ordered 30 diode arrays – enough to do two boards with a couple left over. I figure that since the PCB is so thin and the diodes are so far apart that it might not be too difficult to mount these. I will try tinning the board contacts, placing the part, and then heating the footprint with an iron from the bottom of the board.
 I am happy to confirm that you get 4 sheets of Pyralux for $30. It is thicker and stiffer than I expected – perhaps because it has 2 oz/ft² copper. I will be etching away most of the copper, so expect that flexibility will improve.
It should be a busy weekend.

 

[mkawa]

not a bad deal at all. as soon as i'm a bit less poor money and time-wise i'll follow your lead and grab some

[wcass]

not a bad deal at all. as soon as i'm a bit less poor money and time-wise i'll follow your lead and grab some

perhaps i'll just send you a sheet if i have any left.

back to the bottom PCB. i just etched a new board and will attempt to mount diodes. i used a new (to me) masking technique where i laser print on a vinyl sheet instead of paper. i also purchased a too-cheap laminator. some advice for anyone reading this, a $20 iron works better than a $20 laminator.

here are some pictures including some extreme close-ups of the best and worst etched spots. the diodes i will be attempting to mount are 1.5mm square.

[mkawa]

PM boost for printing and lamination.

this looks like it will be really high quality with right equipment. how good are you at negotation? i think this is sufficient as a proof of concept, and i don't see any other reasonably priced options. we're going to need a lot of pyralux

[wcass]

the Pyrolux was a little hard to work with, but i think it will work well. the stuff i have has extra thick copper (2oz) so it took forever to etch it off. i started with my usual HCl + H²O² and that went from clear to green to almost black. i had to re-oxygenate it and start again twice (re-applying toner on top of the old toner).

[mkawa]

looks like we're going to need a minimum width per trace rule of thumb.

hmm.. i wonder if BOST's printers can even handle 2oz..

wait, what am i thinking, they're just printing on the screening material. durrrr

[wcass]

the controller is complete. i need to etch a new bottom PCB and it should be fully functional; i just need to make it pretty. i got some aluminum samples in the mail from Brunner Enterprises - very high sheen and the profile is perfect for the front edge. i will be using standard 1" angle for the rear edge.

[wcass]

almost done. 3 new pictures.
controller top

controller back edge

caps lock and num lock LEDs

[dorkvader]

This is excellent! It's also using my favourite case! This is pretty much (almost  my ideal "small" keyboard.

I'm really excited about this project, now. I'll finally have something I can use my F XT for!

[pasph]

Wow!

[rknize]

Looking really good, wcass.

[mkawa]

holy crap this is effing fantastic. YOU HAVE DONE IT WCASS

crap, i may have to start a new account on ebay (deleted mine because of that horrible spam email they sent out recently -- no joke) to pick up a pack of this stuff and have boos- sorry BOST print and laminate/etch out a couple circuits..

[The_Beast]

Nice, I'll be doing the same to one of my fullsized M's when I get some time this summer.


Wood cased 60% BS Model M...



hold on, I need to change my pants....

[mkawa]

wcass, could you start a negotiation with these pyralux guys and see if we can get good bulk discounts? something on the order of 20-40 pieces of material

[wcass]

i'm not sure this type is the best fit. the substrate is 1 mil instead of 3 and the copper is very heavy (2 oz). Dupont makes a different type with 3 mil substrate and 1 oz copper that should be a better fit.

with this keyboard i am getting phantom key presses that i believe are caused by the substrate bending too easily. doubling up the separator sheet might resolve the issue, but i don't know.

i bought some Circuit Writer - i think you said you tried this with poor results, but i will also try sintering (which is part of the silkscreen process).

and if that doesn't work then i will try the "rapid prototype" service from InkJetFlex.com

let me know if you would like to try the Pyralux and i will send you a sheet.

[mkawa]

hmm, that is a pain. i figured the only stuff floating out there _was_ the dupont stuff. 3 mil 1oz cu is exactly what we want. the dupont MOQ is like 1000 sheets though.

and yah, circuitwriter is worthless if you just follow the instructions.

[wcass]

and yah, circuitwriter is worthless if you just follow the instructions.

the direction i got suggest to "cure" it by placing a 40watt bulb 6" away for 4 hours. did you to that?

the data sheet for polyester sheet suggest that if you apply heat, it will shrink - but it can then be reheated up to that temp without shrinking more. i tested a sheet of 3mil drafting poly by baking it in an oven at 350 F for 15 minutes. shrinkage was about 1.5% (.2" from 12") and caused ripples. i might try sandwiching it between glass sheets in the hot Florida sun. i also might try to find something that will erase the lines on an "original equipment" membrane and remake the connections.

[mkawa]

i can't remember exactly how i cured it, but i did cure it with heat for a day or so. it did not like the M FCB material (which is probably a polyvinyl) with whatever my curing strategy is. it's meant for rougher PCB surfaces, so i can see that.

it's possible that what it needs is more texture on the surface. maybe a primer and then a very dry high temp cure?

regardless, it's so freaking expensive that it won't scale just because of that. anything whose base material is silver is not going to work out.

speaking of texture, erasers made for erasing ink (available at any art store) will kill oem copper traces.

[wcass]

the art-supply drafting sheet i have is matte textured on one side, so it might work better.
http://www.pearlpaint.com/buy-11-x-17--.003-Single-Matte-Mylar-Drafting-Film_6935_6934_840627.html
 
i will be picking up this tape for masking the lines.
http://www.maniacshobbycomplex.com/stripe-tape-black-1-16.html

[mkawa]

if you're going to try this, try using a copper ink like emikote instead of a circuitwriter.. (in general the emi shielding solutions are much better pricewise than the silver ones for obvious reasons, but resistivity is somewhat uncool..)

[Matt3o]

too many interesting projects to follow. I quit.

[wcass]

i will be adding diodes to the bottom membrane this week. i am using MMBD4148PLM which have five diode elements in a 0.5mm thick, 1.5mm square package. 14 of these will go above the top row - outside of the key area so that they will not interfere with the top membrane or hammers. the picture is taken using the maximum resolution on my flatbed scanner.


it took me an hour to get the first two on and passing connectivity tests. the first thing to go wrong was that i put them both on the wrong way around. even with 40x magnification i could not detect which pin was pin one. putting it on wrong left one key dead, so i had to pull them both off and put them back on again. only 12 more to go for this keyboard.

[damorgue]

How resistant are they to bending. Ideally, once installed it shouldn't flex much, but I imagine one could accidentally bend it during installation. Does any of the soldering joints get loose in such a scenario?

Great progress. One step closer to a custom BS board.

[wcass]

How resistant are they to bending. Ideally, once installed it shouldn't flex much, but I imagine one could accidentally bend it during installation. Does any of the soldering joints get loose in such a scenario?

the footprint is so small that they should be unaffected by casual bending. the back plate has a curve, about 10.5" radius. if any of the diodes loose connectivity during this, i will report it. if all works well with my DIY tests and there is interest, i would like to get a group buy going to get PCB/membrane sets professionally made.

I think there are several other guys working on custom buckling spring projects - if any of you are interested in help or would like to collaborate, let me know and i will send you what help i can. I could use some help on this project with sheet metal work (cut, bend, break) and woodwork (CNC).

[damorgue]

Yeah, true, such a small footprint will not be affected much by flexing. I was more wondering about teensy or similar controllers. Did you solder a ribbon cable to another PCB, solder individual wires from the membrane to the controller or solder the controller straight to the membrane?

[wcass]

the controller is a Teensy++ and it attaches to the matrix using right angle FFC connectors (IBM model M uses vertical FFC connectors) - see pictures in posts 92, 70, and 35. also coming off the Teensy is a ground wire and 3 pin header for caps and num lock LEDs.

[dfj]

I tried my hand at doing a custom M membrane a couple of years back:
  The M has the advantage that parts are readily available, both on the used market, and also from Unicomp to some degree.
  I ended up getting waylaid by the F, so ultimately I hope to approach the M->nkro/custom layouts problem very differently next year via an F-conversion of some sort... here's hoping. :)

  So - my biggest fear is that the the silver printed pads and copper base will electrocorrode, or the base will work harden, or stretch and bump up, etc.. under the small, but unending impacts of the M hammers.
  Two things I found that helped a bit, is like on the F, you want some sort of level base for the hammer feet to rest on to the upper right and left of each contact. My samples here don't have that, but you can see the spots I mean as they leave two dents on either side beside each hammer dent on the rubber mat above.
  Another thing is that you want a fill - a subsequent attempt I was intending to combine the fill with the pads above. The fill serves to reduce the load on the acid when etching and make it easier to get a sharp clean cut with less undercutting, pinholes etc...
  Doing multiple small etches also helps when at home.
My intent was obviously to do a diode array on the controller, rather than try to mix it in with the matrix, adds cost in connectors, but avoids many questions of wear over time.
  If I were to do it again, my intent had been to slice up a couple of normal M membranes and pull out the matrix entirely, avoiding any rework of the M switch which is an old, well tested, long-living mechanism.
  These days - I have explored more about ordering thin pcb, and it is much cheaper than custom membrane for small orders. I'd have them finished in thick nickel to more closely match the electro-corrosive constants for the silver ink. Stuff you might want to explore when you next want to do a full redesign - clearly this path you are exploring is bearing too much fruit to not follow to its end. :)
  Also - silver plated copper particle inks are an alternative to pure silver inks, and somewhat more economical.

Great progress, though - and so pretty!
dfj

[wcass]

funny, i went to this method because i couldn't figure out how to do a capacitive controller. i did read your work on the subject, but it was beyond me. the only programming i know is the simple stuff like ASP and VBScript. that said, i have several XT's and parts should you need anything. i don't sell - i give.

[dfj]

Awww shucks, too kind.
  Luckily, a fresh thread has popped with another approach (closer to the original patents, even) for the cap sensing, though the fellow is doing his testing on the Beam Springs first. Key is that his descriptions are much more lucid than my own babble. :)
http://geekhack.org/index.php?topic=45097

  I have a new rev of my controller coming out soon, which some folks here are helping to test. I'll be posting a preliminary schematic shortly - the exact choices of parts is not quite right, since it was based on what I had lying around - however it will get a couple of folks playing with prototypes, and will be easy to solder up as it's teensy based. The final parts will be very close to the same, just with slight improvements to cost, availability, ease of assembly, and performance (depending on the part, clearly).

dfj

PS - thanks but save all your parts for other crazy projects, I have collected more than my fair share over the years. :p

[korrelate]

i submitted RFQ's to three membrane switch manufacturers requesting ...

I am trying to get replacement parts for a computer keyboard; very low volume. I do not need color, adhesive, embossing, domes, or connectors – I just need membranes with conductive print.

Material = polyester, DuPont 5021 or similar
Thickness = 0.075mm
Size = 300mm x 130mm
Print area = ~10%
Quantity = 5

i'll let you know if i get a bite.

On an unrelated note, i did a drawing of an idea i had for an M60 case. the basic idea was a milled upper and sides (aluminum or hardwood) and a sheet metal bottom. i was not planning on sharing it, but ...
(Attachment Link)

• 5.74 inches is nothing to brag about.
• ribbed for her pleasure.
• as you can see, the testicles have not descended.

Every time I just go strolling through geekhack I am amazed at the variety of issues that people have spent time addressing. Just amazed. Very cool stuff here.

[wcass]

OK, so i got all my diodes mounted and i put my keyboard together, and ... nothing worked. talking with Hasu, it looks like my diodes may be facing the wrong way. my diode arrays are common cathode and it looks like i need common anode.

so i went looking for common anode diode arrays and found nothing in the package size that i wanted. i was looking for a "standard" p-n type diode array, but does it have to be? can i use an "avalanche" or "TVS" type diode if the signal voltage is below the reverse bias voltage? if so, then i might be able to use DMF05LCFLP which has the same footprint as what i am using now.


i think i need to post this question in a different forum.

[mkawa]

actually i can answer this one. avalanche and TVS diodes (which are a variant on avalanches with a shunt) are only different from standard doped semis and other typical diodes in failure mode (ie, their breakdown behavior at high reverse/bias voltages is faster/better than standard semis et al). so yah, you're good to go with TVS or avalanches. prices are probably a little bit higher though.

[wcass]

actually i can answer this one. avalanche and TVS diodes (which are a variant on avalanches with a shunt) are only different from standard doped semis and other typical diodes in failure mode (ie, their breakdown behavior at high reverse/bias voltages is faster/better than standard semis et al). so yah, you're good to go with TVS or avalanches. prices are probably a little bit higher though.

.32 * 15 = $5.52
i think i can handle that. just hope they get here in time for me to have a working M60 for the KeyCon.

Thanks for the confirmation!

[mkawa]

hey did IJflex ever get back to you on low but non-one quantity pricing? how many can they give me for a hundred bucks, for example?

[wcass]

sorry, but i didn't ask yet. nor did i update the SSK membrane rivet holes. i got sidetracked by work and medical issues (not me - mother, wife, and dog).

i'll try to put in my order this weekend so that it might arrive by Aug 15. best to see material and quality before making a commitment.

[mkawa]

meh, deal with it after keycon. i'll see if i can find the time to work up a hacked up membrane assembly in time for keycon (although come to think of it i don't even think i have time to make the sheet metal order, crap)

[wcass]

two membranes just came in printed by inkjetflex. the quality and thickness feels very good (that's what she said). i need to cut them out and punch holes.

the cost for this was about $10 per sheet (plus flat $30 for set up and delivery) - expensive for just two, but reasonable at higher volumes.

they printed some extra stuff and i would like to share some free samples to an anyone interested - PM me with your postal address and any part of this graphic you would like me to send.

[dfj]

wcass - so.... tell us how it went?
 
excited
dfj

[mkawa]

also excited

[wcass]

well, there were two remaining issues; the PCB had the diodes the wrong way around and i still need to verify that the new membranes are a better material for actual membrane.

the i got two membranes from inkjetflex.com and they look like they will work very well - print quality is excellent and no real work to get them going (just cut outline and punch the rivet holes). the setup and delivery was expensive for just two membranes, but this is a real option if done in volume where cost per sheet approaches $10 ($12 each @ 14). 

i got new diodes that should work, but need to make another PCB. DIY PCB production at this size is difficult. i only have the materials to do this using the "toner transfer method". my transfer mediums so far have been unreliable in that it either shrinks to much, doesn't hold enough toner, holds the toner too well, or does not provide the fine detail required for the diodes. i ordered some special transfer paper from China early last month and it just got here yesterday. it did not come in a tube or photo mailer - it was rolled up WITH A RUBBER BAND AROUND IT, then bubble wrapped, so it has some significant creases in it. i am going to iron a sheet out this weekend to see if it gets rid of the wrinkles and performs as needed.

i have a few ideas that i would like to try for a simple but visually appealing case; polished aluminum front edge and back edge, aluminum sheet metal bottom, and wood sides. the front and back would be these:
http://www.brunnerent.com/Tools/Portfolio/frontend/item.asp?type=11&size=0&lngDisplay=0&jPageNumber=6&strMetaTag=
http://www.brunnerent.com/Tools/Portfolio/frontend/item.asp?type=16&size=0&lngDisplay=0&jPageNumber=1&strMetaTag=

i have no real woodworking skills, so i thought that i would have the sides 3D printed for the prototype. i have 2D drawings and a SketchUp model of the sides, but i don't have the software to make a proper file for printing. i will try out Autodesk 123D if time allows.

Thanks

[mkawa]

i ordered some special transfer paper from China early last month and it just got here yesterday. it did not come in a tube or photo mailer - it was rolled up WITH A RUBBER BAND AROUND IT, then bubble wrapped, so it has some significant creases in it. i am going to iron a sheet out this weekend to see if it gets rid of the wrinkles and performs as needed.

TIC man

i have no real woodworking skills, so i thought that i would have the sides 3D printed for the prototype. i have 2D drawings and a SketchUp model of the sides, but i don't have the software to make a proper file for printing. i will try out Autodesk 123D if time allows.

try blender if you're sticking to free software. i don't like how sketchup handles intersections. they become a proper mess. is the arc radius the same as the full sized M/SSK? i'll send you a copy of our prototype arc side holder things when i get the printer back up

heck, we can scale the case we have for the ssk down to your size without a heck of a lot of modification. the fcb work is the biggest pita.

[CPTBadAss]

wcass, you're so handsome. I'M SO EXCITED FOR THIS PROJECT.

* CPTBadAss drools until he passes out from dehydration

[Binge]

I'm very interested to see how this goes

[MOZ]

MY GOD!

[wcass]

well, i went through 8 sheets of transfer paper from two different printers and was not able to get one transfer that i was satisfied with. i have come to the conclusion that i need to invest in the photoresist method.

i just ordered this:
http://www.ebay.com/itm/151034351056

[CPTBadAss]

Could you elaborate some more on the photoresist method wcass?

[wcass]

PCB manufacture is a subtractive process (in most cases). You start with a board covered with copper and then remove copper where it is not supposed to be. This is most often done by applying an "etch resistant" to the areas where you want copper pads and traces and then submerge the board in a solution that dissolves the exposed copper.

The cheap/easy/beginner method of applying an etch resist is the "toner transfer" method. For this, you print a mirror of your design on a laser printer then transfer the toner from the paper to a blank copper clad board using a regular cloths iron or laminator. Laser printer toner is actually plastic which makes a nice resist, but it doesn't stick everywhere it is supposed to; specifically fills of any size at all. It is also limited in what it can do with fine detail.

The "photoresist" method first coats the copper clad board with a chemical that changes it's properties when it is exposed to light and "developed". You print your design on a transparency (negative or positive depending on the properties of the chemical used). The board is then sandwiched with the transparency between sheets of glass, and exposed to light. Light shines on the photoresist where the transparency is clear but can not where it is printed. When the exposure is correct you remove the board from light and dump it into the developer. The developer will either harden the area exposed to light (for "negative" type photoresist) or dissolve the area exposed to light (for "positive" type photoresist).

The pros use photoresist.

DIY PCBs are only cost effective for prototypes or very small runs. To order a PCB of this size from a PCB manufacturer in China would cost about $100 to do one, or about $150 for 15 (about $10 each). Each of my DIY PCB's are costing me about 2 hours and $15 in materials.

[mkawa]

ladyada/adafruit has a fantastic write-up on photoresist etching by the way:

http://www.ladyada.net/library/pcb/inhouseetch.html

if you haven't seen it.

[YakMN]

wcass, is your plan to keep making your prototypes "by hand" until you get it working the way you want it, and then do an order from a manufacturer in China? A GB, if you will.

[wcass]

wcass, is your plan to keep making your prototypes "by hand" until you get it working the way you want it, and then do an order from a manufacturer in China? A GB, if you will.

that is the short term goal. the long term goal is to convince Unicomp that it might be worth it if they built these. if/when we do a group buy, i'ld like to factor in one to send to the guys there in Lexington.

[CPTBadAss]

Deliver it to me and I'll personally drive down to Lexington to convince them to make it.

Also, thanks for the info on photoresist wcass and mkawa!

[YakMN]

ah, that IS ambitious. I thought we were all going to be going around destroying IBM typewriters to get at their hammers and barrels, and spending our lives cutting them apart and lining them up over the new membrane(s). Much better if an actual manufacturer does it of course. (not quite as much fun perhaps).

Wouldn't we also have to make a new controller for them? I mean, if you use the old controller with the new layout, it's not going to know about Fns, etc. They won't be able to sell a small keyboard without fn layers.

Anyway, if there's anything I can do to help, please let me know. (err, NON-technical help

[mkawa]

unicomp is unable to do short-run membranes

[wcass]

Wouldn't we also have to make a new controller for them? I mean, if you use the old controller with the new layout, it's not going to know about Fns, etc. They won't be able to sell a small keyboard without fn layers.

The new controller is a Teensy++ with a couple of connectors soldered to it. Total cost is $30. See a picture in post #92 of this thread. A manufactured version might have the AT90USB1286 chip on the "bottom membrane" allowing reduced part count, size, and cost.

[The_Beast]

unicomp is unable to do short-run membranes

What would the minimum order quantity be?

[dgreekstallion]

Excellent thread, very informative.

[tinco]

Hi, I've recently took the keyboard from an IBM 6715 typewriter, to mod it into a keyboard. The key layout itself is nice and small (60%) but the barrel plate and membranes stick out a lot all around it, so I'm looking to either cut and patch with copper tape like hasu did here http://geekhack.org/index.php?topic=29483.0 or make a new ones from scratch.

This discussion got me wondering.. what if I just make the layout out of thin copper wire, and flatten it with a hammer? It seems rather crude, but it's surely a lot cheaper than printing on clear sheets for $10 per sheet, and doesn't require much skill in creating the right pdfs and such.

Is there anything that would prevent this from working out well? It's just a silly idea I had

[wcass]

i tried using copper tape without much luck. i think there was too much wrinkle. in my experience, the membrane needs to be perfectly flat. i would think that DIY flattened wire would be less flat than copper tape. but if you have the time to try it out, please do so and let us know if it worked for you.

[tinco]

Alright, I'll see what my options are when I pull it apart. To be sure, the only reason it needs to be very flat is because else it won't fit between the plastic and the backplate right? Was the problem you had with copper tape that it didn't fit back together or that it wouldn't register keypresses?

Thanks for the info!

[wcass]

Alright, I'll see what my options are when I pull it apart. To be sure, the only reason it needs to be very flat is because else it won't fit between the plastic and the backplate right? Was the problem you had with copper tape that it didn't fit back together or that it wouldn't register keypresses?

ghost keys. when i pressed a key, neighbor keys would register.

[wcass]

i finally got all of the stuff i needed to do the "photoresist" PCB method and the results are fantastic.

dry film photoresist - $15 eBay
amber LED spot "safe" light - $6 ebay
sodium carbonate - $7 grocery store
Duralar polyester drafting film - $4 art supply store

So about $33 for enough supplies to do a bunch of different designs. I'm thinking about my XTant project and doing a bottom that will fit the SSK revival.

I'm off to solder on some diodes.

[mashby]

I love watching a master at work! 

[mkawa]

unicomp is unable to do short-run membranes

What would the minimum order quantity be?

iirc it was between 500 and 1000

[wcass]

SUCCESS!

Despite doing a truly awful job at soldering on the diodes, > 50% of the keys are working exactly as they were designed to do. The keys that don't work are the top and bottom rows (Esc, numbers; Ctrl, Alt, GUI, Space, left, down, right), and two columns (Y, H, B; close bracket, Enter, right Shift).

I tested for NKRO using AquaKey. Every combination of WASDQZ that i tried yielded correct result.

So now i disassemble and try to resolve the issues with the dead columns and rows. I'm sure my poor job with the diodes is the problem with the columns, but not sure about the rows.

[bcg]

SUCCESS!

Despite doing a truly awful job at soldering on the diodes, > 50% of the keys are working exactly as they were designed to do. The keys that don't work are the top and bottom rows (Esc, numbers; Ctrl, Alt, GUI, Space, left, down, right), and two columns (Y, H, B; close bracket, Enter, right Shift).

I tested for NKRO using AquaKey. Every combination of WASDQZ that i tried yielded correct result.

So now i disassemble and try to resolve the issues with the dead columns and rows. I'm sure my poor job with the diodes is the problem with the columns, but not sure about the rows.

Wow!  Just read this entire thread, nice work!

Can you recap what materials and production methods you're using now, there were so many iterations that I got a little lost

[CPTBadAss]

SUCCESS!

Despite doing a truly awful job at soldering on the diodes, > 50% of the keys are working exactly as they were designed to do. The keys that don't work are the top and bottom rows (Esc, numbers; Ctrl, Alt, GUI, Space, left, down, right), and two columns (Y, H, B; close bracket, Enter, right Shift).

I tested for NKRO using AquaKey. Every combination of WASDQZ that i tried yielded correct result.

So now i disassemble and try to resolve the issues with the dead columns and rows. I'm sure my poor job with the diodes is the problem with the columns, but not sure about the rows.

Hooray!! Great job wcass!!

[wcass]

...

Can you recap what materials and production methods you're using now, there were so many iterations that I got a little lost

Membranes keyboards are cheap if produced in LARGE volume ($5 a set at 5000 units); in small volume, they are actually quite expensive ($100 a set at 5 units). They are also reliable, but the design does not lend itself to adding diodes mid-circuit for back-flow prevention. In other words, two key roll-over at best. This is an experiment trying to create custom membranes that are relatively inexpensive at low volume, and also introduce diodes into the design to enable NKRO.

A Membrane keyboard matrix consists of 3 thin layers sandwiched together; a bottom conductor layer with traces on its top side, a top conductor layer with traces on its bottom side, and a middle separator layer with no traces but holes where the keys would be. When you press on a “key” the thin top layer deforms a little over the hole in the middle layer and a conductive trace on the top layer touches a trace on the bottom layer to complete a circuit and register a key-press. 

Any “lumps” in the layer sandwich would change the way that the top layer deforms so placing diodes near the keys would probably prevent proper operation. I avoided this by making the bottom layer larger than the other layers and putting diodes on the bottom layer outside the border of the top and middle layers. By using diode arrays, I keep the chip count low and also join a group of keys into a logical column. I used 14 5x diodes for this, but other unidirectional “TVS” diode array should work.
http://www.digikey.com/product-search/en?x=0&y=0&lang=en&site=us&KeyWords=DMF05LCFLP

My bottom layer is an 8 mil (.2mm) thick PCB which is usually the thinnest substrate available from manufacturers. I made my own and assembled it myself, but do not recommend anyone else doing this except for a prototype. My middle layer is from a Model M but cut down to the right size. My top layer is 4 mil thick plastic film that I had printed at InJetFlex.
http://inkjetflex.com/site/substrate-materials-rapid-prototypin

Other parts of my M-60 project include …

• steel back plate, mat, hammers, springs, key caps from a donor Model M
• barrel frame and key caps from Unicomp
• USB panel mount , Teensy++ from PJRC
• FFC connectors from Digikey
• 20 gauge steel sheet from Home Depot

[Hellmark]

How feasible would it be to offload the diodes into a PCB that the membrane connects to?

[wcass]

How feasible would it be to offload the diodes into a PCB that the membrane connects to?

It would require one connector pin per key, so would need a connector something like this:

[Hellmark]

Something like that is completely doable, even if you ran in a couple ribbon cables.

[damorgue]

How are the sheets cut? Another option might be to put holes in the top layer at the locations where the diodes are placed if you place them next to their respective switches on the bottom layer.

You mentioned approximate prices for very large and small quantities. How much are they in medium quantities? I don't expect 5000 to be sold and 5 is few even for a prototype run.

[bcg]

Membranes keyboards are cheap if produced in LARGE volume ($5 a set at 5000 units); in small volume, they are actually quite expensive ($100 a set at 5 units). They are also reliable, but the design does not lend itself to adding diodes mid-circuit for back-flow prevention. In other words, two key roll-over at best. This is an experiment trying to create custom membranes that are relatively inexpensive at low volume, and also introduce diodes into the design to enable NKRO.

A Membrane keyboard matrix consists of 3 thin layers sandwiched together; a bottom conductor layer with traces on its top side, a top conductor layer with traces on its bottom side, and a middle separator layer with no traces but holes where the keys would be. When you press on a “key” the thin top layer deforms a little over the hole in the middle layer and a conductive trace on the top layer touches a trace on the bottom layer to complete a circuit and register a key-press. 

IMO your design is very sensible and I think it is a solution that doesn't stray too far from the original engineering.

The solution of running individual traces to the controller (as opposed to a matrix) seems kludgy and also if you have individual lines going to the controller anyhow, it might make more sense to just use shift registers instead of those diodes.  I'm sure soldering those tiny qfn packages is a blast

This looks really good and I look forward to testing it out.  I've not etched PCB before but I'm not opposed to giving it a shot... but what is the quantity of PCBs that it makes sense to have a tested design fabricated?

Also I'm sure not an expert on this stuff but unless I'm missing something think it might be possible to do the NKRO in software... I'm going to think about it a bit more and if I haven't decided that my idea is completely stupid, I'll post what I'm thinking so that you guys can convince it is

Anyhow great job wcass!

EDIT:

BTW, how do you cut the steel plate?

[wcass]

How are the sheets cut? Another option might be to put holes in the top layer at the locations where the diodes are placed if you place them next to their respective switches on the bottom layer.

You mentioned approximate prices for very large and small quantities. How much are they in medium quantities? I don't expect 5000 to be sold and 5 is few even for a prototype run.

Sheets are cut by hand. I thought about creating holes for the diodes and even considered putting them on the back (with holes in the back plate), but this idea seemed simplest and most likely to succeed.

Traditional silver silkscreen membranes cost a lot to do the first one (make frame, pattern, tooling, etc), and the last one (break down, clean and store tooling). Every one in the middle costs $4. The copper membranes from InkJetFlex are $50 for the first two and $10 each after that.

IMO your design is very sensible and I think it is a solution that doesn't stray too far from the original engineering.

The solution of running individual traces to the controller (as opposed to a matrix) seems kludgy and also if you have individual lines going to the controller anyhow, it might make more sense to just use shift registers instead of those diodes.  I'm sure soldering those tiny qfn packages is a blast

This looks really good and I look forward to testing it out.  I've not etched PCB before but I'm not opposed to giving it a shot... but what is the quantity of PCBs that it makes sense to have a tested design fabricated?

Also I'm sure not an expert on this stuff but unless I'm missing something think it might be possible to do the NKRO in software... I'm going to think about it a bit more and if I haven't decided that my idea is completely stupid, I'll post what I'm thinking so that you guys can convince it is

Anyhow great job wcass!

EDIT:

BTW, how do you cut the steel plate?

Thanks for the praise. I wasn't 100% sure that it would work, so that's why I went DIY. Now that i know it does work, it might be time to price a group buy of PCBs with assembly. I've never done a group buy, so i would want to team up with someone who has.

I cut my steel plate using a jig saw with metal cutting blade. If this does become a group buy, you can expect me to do several videos showing and explaining every step of the assembly.

[damorgue]

Ideally we should make a run of custom BS boards later on with all the other parts as well. These are replacement membranes which fit current boards, correct?

[Melvang]

While I haven't been following this thread like I should be (since it is paving the way to custom layout BS boards) would it be feasible to do membrane top and middle layer with a PCB on the bottom layer?  This would allow full diode placement using SMD.  Just thinking out loud here.  If it isn't feasible at all I understand.

[Hellmark]

The only problem is that you'd have to have a curved PCB. M's have a curved steel plate. While most get their normal curve by having different key shapes, M has uniform key shape and curved plate.

[Melvang]

The only problem is that you'd have to have a curved PCB. M's have a curved steel plate. While most get their normal curve by having different key shapes, M has uniform key shape and curved plate.

I am guessing that having curved PCB's made would be borderline prohibitively expensive?

[Hellmark]

Yup. Copper clad boards are always done on flat sheets, unless you custom order it. Also, the materials it is made from don't take to flex well. Trying to curve it would just break it.

[Melvang]

Yup. Copper clad boards are always done on flat sheets, unless you custom order it. Also, the materials it is made from don't take to flex well. Trying to curve it would just break it.

I wonder if any online shops can do curved PCBs.  Or if it would be easier to have caps made to work with a flat pcb?  The only reason I am suggestion this would be for easier custom cases/layouts.

[regack]

Yup. Copper clad boards are always done on flat sheets, unless you custom order it. Also, the materials it is made from don't take to flex well. Trying to curve it would just break it.

I wonder if any online shops can do curved PCBs.  Or if it would be easier to have caps made to work with a flat pcb?  The only reason I am suggestion this would be for easier custom cases/layouts.

How about a series of horizontal flat PCBs that follow the curve of the plate and are joined by flexible interconnects.

[Melvang]

Yup. Copper clad boards are always done on flat sheets, unless you custom order it. Also, the materials it is made from don't take to flex well. Trying to curve it would just break it.

I wonder if any online shops can do curved PCBs.  Or if it would be easier to have caps made to work with a flat pcb?  The only reason I am suggestion this would be for easier custom cases/layouts.

How about a series of horizontal flat PCBs that follow the curve of the plate and are joined by flexible interconnects.

We can't be having any of that.  That makes to much sense.

[Hellmark]

Having a bunch of little PCBs could be a bit of a pain, as it adds a lot of places for things to go wrong, and a ton more soldering.

What I personally would suggest, and this may be something that would be of far greater interest, would be to have flat PCB, and keystems designed to take MX keycaps. That way, you could have flat boards if you wanted, since those do seem to be quite popular, and if you do want a contoured shape of the keys, then you could go get keys that are sculpted that way. It would require custom fabrication of plastic parts, and injection molds are expensive, but I think a crap ton of people would be interested in something like that.

[CPTBadAss]

Would your idea be cool Hellmark? Personally I like the keycaps and curve of a Buckling Spring board and think its part of the charm. But that doesn't mean I think its a bad idea and could be cool. Do we have enough people to support buying new keycap molds and custom plastic molding for new parts? I doubt it.

Unfortunately I don't think there's enough demand to help fund the effort...or a manufacturer that would do low volume stuff like that.

[Hellmark]

Thinking about it, it might be possible for us to make curved PCBs. We just need to find a way to get some sort of heat resistant material curved, and then copper plate it. Copper plating should be semi decent to do, and done in most cities, since it is a step in chrome plating of car parts. The big thing is finding a heat resistant material that could withstand curving.

[CarVac]

If you want to subject yourself to the hazards of phenolic resin, you can lay up the fiberglass/phenolic board on a curved surface by hand. That way you won't need to bend a premade part.

Epoxy is slightly inferior as a resin for circuit boards, but for a keyboard that doesn't need the heat or fire resistance of FR4, you could do it without needing high-temp curing.

[wcass]

While I haven't been following this thread like I should be (since it is paving the way to custom layout BS boards) would it be feasible to do membrane top and middle layer with a PCB on the bottom layer?  This would allow full diode placement using SMD.  Just thinking out loud here.  If it isn't feasible at all I understand.

That is exactly what i have done.

The PCB base matirial i use is .2mm (or 8mil) thick. This is the thinnest commonly avaiable from PCB fabs. This material is flat, but will take the gentle curve of an M backplane without breaking. I should sumerize this whole thread when i get home.

[tinco]

Did you cut holes in the membranes for the diodes? Wouldn't they be crushed between the steel plate and the plastic?

[wcass]

the keys are where the red is. blue arrows point to where the left 3 diode arrays are. these 3 chips handle 15 keys.

some pictures of the controller and how the membrane and PCB attaches



older picture, but still accurate:

[bcg]

some pictures of the controller and how the membrane and PCB attaches

hasu pointed me in the right direction to integrate Adafruit's Bluefruit controller with the tmk firmware to make a Bluetooth keyboard; not many extra components for this, just:

the Bluefruit board (http://www.adafruit.com/products/1535 - $19.95)
charge controller (http://www.adafruit.com/products/259 - $12.95)
battery (http://www.adafruit.com/products/328 - $14.95)
plus misc components like switches or buttons for pairing, LEDs for status idicators, etc

Maybe could get these components cheaper but I haven't looked that hard yet. 
My goal is to get to the point where I could plug the keyboard into USB for charging & for use with computers that don't have bluetooth, and unplug it and switch over to bluetooth for use with a laptop or another device.  Anyhow I was thinking I would want to solder everything up to a single PCB - its not obvious to me how you have the teensy attached to the bottom membrane, but since that is through-hole it would probably be easy to attach anything in the manner, right?

I have some working code already and can type with a Model M over the bluefruit controller, but I think the first version of that device doesn't support raw HID reports very well... they are sending me a replacement that is the newest version, which is nice because that also supports mouse & media controls so I should be able to easily enable those features in the firmware so that you could use hasu's mouse keys and control volume etc.  All I really have left to program is the logic to switch between USB and bluetooth to make this happen.

BTW what are the the three header pins sticking off of the teensy; are those for your lock LEDs?

[wcass]

I'll watch for your progress.
Yes, the 3 pins are for num lock and caps lock (and +5).

The controller is connected to the PCB by a 17 pin "right angle" FFC. This makes it very easy to assemble and disassemble but hard to take a picture of. Here is a picture of the top membrane fitting into a similar 5 pin "strait" FFC that connects the top membrane.


I wanted to share my method for assembling the key switch layers that solves one of the common problems when assembling a buckling spring keyboard.

The springs on BS switches are a little longer than the frame barrels are deep so that if the barrel frame top is flat against a surface then the springs will not seat properly. My previous solution for this was to use whatever junk i had on hand to wedge around the edge of the frame to prop it up. The problem with this is that a slight bump might knock one of the props loose and some of the springs will unseat.

I start with a box about the size of the keyboard and cut a hole just big enough to fit around the barrels. Pictures show it best. Also showing the assembly steps.

springs in and nicely seated

pad

top membrane with contacts face up

middle membrane is clear, so it looks the same as the picture above.
bottom membrane (OK, it is a PCB) with contacts face down

back plate

nuts on and controller attached. tape keeps LED wires from getting pinched.

[dgreekstallion]

^^^^


You are a genius. I salute to you, sir.

[bcg]

I'll watch for your progress.
Yes, the 3 pins are for num lock and caps lock (and +5).

The controller is connected to the PCB by a 17 pin "right angle" FFC. This makes it very easy to assemble and disassemble but hard to take a picture of. Here is a picture of the top membrane fitting into a similar 5 pin "strait" FFC that connects the top membrane.

Ok, I see now.  That looks like it would be easy to connect another PCB or something to mount the controller & other components.  I have my bluetooth circuit & code working well now, and it should be easy enough to integrate with anything using hasu's firmware.  I'm going to post the details to a separate thread, but its a really busy time for me so it might be a bit before I can do that.

Sort of off topic, but did you order all of your keys new from Unicomp?  Or did you harvest them from other boards?  Just curious because I'd like to get some alpha keys with the number pad printed on them like on an original SSK

[wcass]

Sort of off topic, but did you order all of your keys new from Unicomp?  Or did you harvest them from other boards?  Just curious because I'd like to get some alpha keys with the number pad printed on them like on an original SSK

most of those keys came new from Unicomp.

[joneslee85]

This is incredible piece of work wcass! You are amazing. I think you should create kick starter campaign to help funding your project and allow you to mass produce it later on.

[bcg]

wcass

Let me know what you think about this product (important part starts at 18:18):

What I'm thinking is to make both sides of the membrane out of the printed sheets, without any PCB etching... then just stick the standard plastic barrier from the Model M in between... at the top of the printed circuit you could have printed terminals and you could attach surface mount I/O expanders or Parallel to Serial Shift Registers ... if you use 8 or 16 bit shift registers you wouldn't need a teensy++ anymore, could use something smaller/cheaper so you could save some cash, also hasu uses 8 bit rows in his matrix array so would be super easy to scan the matrix... plus no cost for the copper clad or the chemicals... just stick the ICs on with the z-tape and then run two flex "cables" to the microcontroller, basically like you're doing now, just without having to solder those tiny QFN diodes

If its durable enough I think it could make this project really feasible.  Could even design the printed sheets as a full 101/103/104 layout and make it so that you could optionally cut off the number pad, arrow keys, function keys, etc to make smaller layouts if you want.

What do you think?  I'm up for splitting the cost of a test run if you're interested...

[wcass]

I looked into Z tape before deciding to do it this way. The diode array i use are really small (1.6mm x 1.6mm); each pad is only .08 mm² and has just .25mm between pads. From the datasheet, the tape needs 3.2 mm² pads minimum and at least .4mm between pads.

But an 8 by X matrix is definitely doable.

[mkawa]

is there a datasheet on the z-tape anywhere? the PSAs with really high tear strength and vibration resistance are ridiculously expensive. i have my doubts about tqfn joints lasting at a curvature under constant vibration.

and then there's the geometric requirements due to resistance of the material. it's a doped dieletric, most likely, and those tend to have really high resistance unless you give them oddly shaped traces.

[bcg]

Yeah, sorry I should have been more clear... I was talking about not using the QFN diodes at all, and using something larger like this:

http://www.digikey.com/product-detail/en/74HC597D,653/568-8161-1-ND/2762851

although if you need 3.2mm that's not really going to work regardless... guess I'll just have to get the photoresist gear to try this out and do as you did wcass

EDIT:  This is what made me think that this would be possible for this project... maybe they have the ICs attached to the flexible circuits via a different method though and the z-tape is just for the sticker part - http://www.crowdsupply.com/chibitronics/circuit-stickers

[bcg]

is there a datasheet on the z-tape anywhere? the PSAs with really high tear strength and vibration resistance are ridiculously expensive. i have my doubts about tqfn joints lasting at a curvature under constant vibration.

and then there's the geometric requirements due to resistance of the material. it's a doped dieletric, most likely, and those tend to have really high resistance unless you give them oddly shaped traces.

Can you define what PSA means?  Google says its a prostate test and to go to the second page of search results would be very 1990's of me...

datasheet: http://www.adafruit.com/datasheets/3m%209703.pdf

[damorgue]

Can you define what PSA means?

Probably Pressure Sensitive Adhesive.

I doubt it is public service announcement

[mkawa]

pressure sensitive adhesive is adhesive that cures when you put compressive force on it. usually they're modified thermosets.

[mkawa]

also i suspect that what's going on with this z-tape is that it's just conductive enough to conduct with the assistance of a large nearby conductor given enough free electrons for current, kind of like a semiconductor but maybe mixed into a siloxane copolymer substrate or something. what i would be afraid of with a model F is that the AC impedance between two geometric points on the tape that are both in contact with different pieces of metal conductor will be non-zero. that is, DC resistance may be infinite, but there will be weird capacitive effects that will screw up the capacitive switches and matrix

[idollar]

impressive work. The reporting was even more impressive.
At the end of this post https://geekhack.org/index.php?topic=40111.msg1102755#msg1102755  there is a picture of the keyboard.
Is this the final keyboard or did you build a different case for it ?

Cheers

[wcass]

Yep, that's it. Very primitive.

I got a Kishsaver, so have not done anything with this since. The next logical step would be to get a proper professionally made PCB and case. Might build a controller onto the bottom membrane.

[ccc24]

is there any change this will be going into production or a GB?

[wcass]

I don't think the cost and quality is good enough to go into production. I did make an attempt to take it to the next level ... custom layout in custom case, professionally produced PCB and membrane, controller built onto the PCB. It was at the 2015 KeyCon.


The membrane + PCB was more than 2x the cost of one PCB and the controller much more difficult to program than xwhatsit's - so why not go model F style?


If you have not seen Ellipse's F62 reproduction thread, check it out.