My Crazy Idea: A Hall-Effect Buckling Spring Switch

[krfkeith]

So, I was reading about BSs on the deskthority which in turn brought me to the patents. Interestingly, one of the ideas for the contact mechanism proposed in the original patent was the idea of using the hall effect. I thought this might be a neat idea to experiment with.  I realize that building your own switches is somewhat non-trivial, however, I don't believe it would be impossible. As I've mentioned in another thread I made, I really want to figure out a way to make a BS keyboard with my own custom layout. So the idea I had was to make Model F-style barrels by molding and casting an original, and then buying the flippies and springs from Unicomp (100 can be had for $20, not too expensive). I would then need to figure out a way to make the plate to hold the Model F barrels. Anyway, all that aside, are there any major flaws in a hall-effect buckling spring that I'm looking over? I've included a drawing I made of a mock-up of the design. Please excuse the poor quality of this though, I'm not an artist! 

[jacobolus]

From what I’ve heard, making buckling spring parts (e.g. the plastic barrels) is extremely difficult because it requires very tight tolerances. That is, just a little bit of variation will dramatically affect the behavior of the switch. [I am not an expert, so this is secondhand advice though.]

[krfkeith]

From what I�ve heard, making buckling spring parts (e.g. the plastic barrels) is extremely difficult because it requires very tight tolerances. That is, just a little bit of variation will dramatically affect the behavior of the switch. [I am not an expert, so this is secondhand advice though.]

I've actually heard/read that too. I guess the question then becomes figuring out a way to cast parts extremely accurately. I imagine this is a function of the shrinkage and dimensional stability of the resin used. Any suggestions and/or experience in this area from anyone here?

[xwhatsit]

You could use hall effect, but if you just  want non-contact sensing then capacitive sensing would be perfectly acceptable (c.f. Model F). I'm not sure what hall effect sensing would gain you in typical usage; it would certainly bulk up the keyboard and make it more expensive (i.e. you can no longer just plonk down a PCB with some capsense pads underneath, you need hall effect sensors under each key which starts getting pricey and bulky).

Nothing wrong with the way it would work though; it would probably last a thousand years too

[krfkeith]

You could use hall effect, but if you just  want non-contact sensing then capacitive sensing would be perfectly acceptable (c.f. Model F). I'm not sure what hall effect sensing would gain you in typical usage; it would certainly bulk up the keyboard and make it more expensive (i.e. you can no longer just plonk down a PCB with some capsense pads underneath, you need hall effect sensors under each key which starts getting pricey and bulky).

Nothing wrong with the way it would work though; it would probably last a thousand years too

Above all, my goal here is to experiment/have fun, so practicality is not my major concern.      That being said, there are, IMO, a few somewhat practical reasons to not use capacitive sensing:

1. I have had issues in the past with reliability of capacitive sensors. To be fair, this is probably just my own fault and/or bias.

2. AFAIK, Unicomp does not sell capacitive flippies, meaning I'd have to make my own and/or harvest them from old keyboards. Making the carbon infused resin is probably beyond my capabilities.

3. I really like the idea of a super reliable keyboard, and hall-effect designs are certainly that. 

4. I don't believe anyone has managed to DIY a capacitive sensing PCB yet, I remember reading in a few other threads about people having trouble with this.

As for price, I actually don't think this would be a huge issue. The magnets themselves are pretty cheep, you can find packs of a 100 or so for around $15. As for the sensors, IIRC, Digikey has them for around $0.40 In quantities of a hundred, or $40 total.

[xwhatsit]

Right-o, I won't stand in the way of anybody doing anything For Science

But on those points:

2. Capacitive flippies are just as easy as gluing magnets to other flippies; you only need glue some aluminium foil or similar and insulate it from the sense pads if necessary

3. Hall effect should have excellent reliability, but a lot of that is down to the mechanism. The Honeywells didn't have the flippy foots slapping a hard surface; replicating the somewhat violent buckling spring mechanism will probably have similar reliability with capacitive or hall effect. Neither are to be sneezed at, however.

4. (Shameless plug) I'll point you over here: http://geekhack.org/index.php?topic=45097.0 and here: http://geekhack.org/index.php?topic=57103.msg1317776#msg1317776

Hall effect sensors used to be a pain, you used to have to use a comparator and mess around with analogue crap, same as with capacitive sensing. However I see they now have some nice latching hall sensors with built-in hysteretic comparators which put out a nice logic-level voltage. Would make things easier!

[fohat.digs]

2. AFAIK, Unicomp does not sell capacitive flippies, meaning I'd have to make my own and/or harvest them from old keyboards. Making the carbon infused resin is probably beyond my capabilities.

The F style is vastly different. I have some that I am holding for the day when/if one of the "XTant" project actually materializes, and it may not be too hard for individuals to buy individual keyboards to strip for parts, but I doubt that these are anything that you will want to be fabricating in quantity.

PS - I think that the correct term for "flippies" is "spring hammers"

[E TwentyNine]

PS - I think that the correct term for "flippies" is "spring hammers"

"Pivot Plate".

[0100010]

Necro post.

http://www.shapeways.com/shops/nfc

Maybe ordering some of these, modding in some magnets to the pivot plates and designing the hall effect PCB would now be possible.