Placing and stabilizing MCU in hand wired keyboard

[Martinsos]

Hi all,
I am working on my first hand wired keyboard and am super excited about it !
Thanks to GeekHack and community on reddit I have already found a lot of information that I need (maybe even too much! choices choices), but one thing I did not find anywhere is how to make sure that MCU (controller) is fixed nicely, and where to put it actually.

So I am going with sandwich case: one switch plate and one bottom plate with standoffs connecting them / keeping distance, no mid plates.
Switches are Alps (Matias) and are going to be handwired.

I was looking at different MCUs and am looking now at: Teensy 2.0, Teensy 3.2, Proton C, Postage Board.

However, what I don't have good idea about is: where should I position my MCU and how do I make sure it holds strongly? Since USB cable gets plugged into it and it will sometimes be plugged out (during travel), I am expecting some amount of stress to be present there, and I am assuming if MCU is not fastened securely it might wobble or fall off.
I think I noticed some people saying that they glue MCU to the plate, but that seems a shame to me since everything so far in my build is snap on (switches) or screws (plates) and I would rather avoid gluing, since that makes it also hard to later change MCU if I wish.
Since I am getting my plate laser cut anyway, I was thinking about adding some extra holes so I can screw in the MCU, but I am not sure how would that go actually hm.
Btw. my keyboard layout is packed so there is no space really for the MCU in between the switches.

There is also this Postage Board that I mentioned, which is especially made for handwiring and is intended to be soldered directly onto three switches. That seemed cool to me, since it could reduce thickness of the keyboard. Looking at it, I figured out that it gets its stability from being soldered to switches + from those extruded parts in MX switches that go through this board. However, Alps (Matias) don't have those extruded parts which means only solder is holding it, and that sounds too weak to me, with USB plugging/unplugging?

Thanks a bunch!

[Anakey]

Hi,I have so far done two hand wired builds, my first, Myth, was a handwired UK78 in ortholinear layout. https://imgur.com/a/G8DKB I had a 1u gap between the main board and the num pad so i used this 1u gap to put the Teensy2++. The MCU is held in place just from being soldered to the wire for the rest of the board so it is suspended without being glued to the plate.

The second board that i have recently completed, Mechamorphosis, was using the postage board this was a 60%. https://imgur.com/a/CB5I4PA I did a livestream series of 3 episodes in which i do some of the wiring live. i will edit this post later when i get home for the link to my youtube/twitch channels so you can watch the vods if you are interested.

If you use about 0.7mm/20AWG magnet wire as i do in my handwires then this will also offer support to the MCU so there will not be as much strain on the solder pins. This is why i prefer to use thicker single cored enameled/magnet wire that will hold its shape when bent and makes for a strong stable support.

hope that helps

[Martinsos]

Thanks for the answer!
Those are some very nice keyboards . On the first one, I see that you "extracted"  USB port to the side of the case and glued/fixed it there and then connected it with wires to Teensy 2. That makes sense, then port will be stable and Teensy is under no stress.
I don't have such case, I have sandwich case (two plates, switch and bottom) so I guess I would have to figure out how to do this.
How hard was it to "extract" that usb port?

Thanks,
Martin

[invariance]

Provided you have the clearance between switch plate and case bottom, mount the controller directly to the bottom with machine screws.  If the bottom is plastic all good, but if it is metallic, use a sheet of heavy plastic to isolate the controller.
Screwing it down would be the ideal way to secure it.


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[Anakey]

Thanks for the answer!
Those are some very nice keyboards . On the first one, I see that you "extracted"  USB port to the side of the case and glued/fixed it there and then connected it with wires to Teensy 2. That makes sense, then port will be stable and Teensy is under no stress.
I don't have such case, I have sandwich case (two plates, switch and bottom) so I guess I would have to figure out how to do this.
How hard was it to "extract" that usb port?

Thanks,
Martin

i accedently ripped a pad when removing the usb port on my first one it is hard to cut out the housing around the port so that you can easily desolder the connector itself, then you have the other hard task of soldering directly onto the original pads without causing shorts. If i had more space i would have left the original port on the teensy and used an extension cable. if the original port was through hole it would have been easy but with surface mount it is too much effort and too easy to damage the pads or short when soldering

[Martinsos]

Provided you have the clearance between switch plate and case bottom, mount the controller directly to the bottom with machine screws.  If the bottom is plastic all good, but if it is metallic, use a sheet of heavy plastic to isolate the controller.
Screwing it down would be the ideal way to secure it.


Sent from my iPhone using Tapatalk

Thanks, that makes sense! I was looking at Teensy 2.0 as an example but had hard time finding a place on it where I could put the screw through. I was thinking of soldering Teensy onto proto board that is slightly wider than Teensy and then screwing the protoboard to the bottom case, although that screwing sounds tricky. How would you approach this, mounting the controller to the bottom?

[invariance]

Forgot the teensy doesn’t have mounting holes
Mounting the controller to a larger photo board sounds like a good option, provided clearance.
Here is another idea https://www.thingiverse.com/thing:167491 .
Something else that you could toy with is using the insulation washers from a TO220 transistor mounting kit to clamp the controller around the outside.

Screwing into the base?  I would use 3mm machine thread screws, drill through the bottom plate with an undersized bit and let the screw tap its own thread.
Threaded inserts for that “professional” finish?
Not wanting to screw into the base?  Hmm that gets interesting.  Would need to bond something to the base first (Perspex?) on which to screw into.


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[Martinsos]

That is nice (3d holder)! Although I am guessing Teensy would get pulled out when unplugging the USB cable.

I am ok with screwing into the base, I will go with that. I measured the width of the teensy and added 4 holes to the bottom plate CAD file, 2 to the left of it and 2 to the right, so I will be able to mount Teensy to some kind of plate and then screw that onto the base. I have yet to figure out what kind of plate to not close the electrical circle with the bottom plate, maybe proto board + plastic beneath it or just plastic hm, I will figure smth out.

I will put photos of what I have done when I get all the components and some time to do it.

Thanks a bunch!

[bitswamp]

Not that I am a handwire expert, but I'm a fan of using a usb extension cable to provide internal strain relief

Something like this https://www.amazon.ca/dp/B00HAOK7XE/ (similar ones are available on Aliexpress for about $1)

Then you can put your controller whereever is convenient and route the cable to the cutout. And since it's cheap, you can freely modify the female end of the connector to fit securely in your case.

[Martinsos]

Cool, this is handy! I ordered Elite C at the end, but I found this extender for USB C on Ali Express.

This is great for removing the strain from the MCU, but still, I need to figure out how to both mount MCU and how to mount the female end of this extension cord. I have an idea how to mount MCU somewhere now (I can screw it on the bottom plate as we discussed above), but would you have any suggestions for the female end of extension cord? Where would you mount that if you had sandwich case with only switch and bottom plate? I don't like the idea of gluing it, but maybe I am being too picky here.

[bitswamp]

Some keyboards have a screw-down plastic guard behind where the cable exits the case, like https://i.imgur.com/GVRzW8M.jpg

It should be possible to make one that fits snugly over the female end of your usb extension. One end should be a little narrower and go over the cable part, the other end will be wider and fit over the enclosure for the female port.

When screwed down tightly to the bottom plate, friction would prevent the adapter from pulling out, and the physical shape would prevent it from being pushed in.

If you have a 3d printer this will be no problem. If not, you could make it out of basswood strips (available at hobby/model shops) or take a piece of junk plastic and drill/dremel it to suit.

[Martinsos]

O I like this, this is awesome idea. I could even glue the female part to this piece of plastic for extra safety, I am ok with that, I just did not want to glue it to the bottom plate. Cool !! Thanks a lot for the inspiration .