[Help] DIY Membrane keyboard

[BadeBhaiya]

Hellp all, hope you're doing well.

For the past few months i have been dabbling in mechanical design and 3D printing stuff. Anyway i was wondering if there's a way to make DIY membrane keyboards. Like the ones on TV remote controls and such. With those black conductive silicone bumps which bridge contact between two "fingers" on the PC board. I don't need volume, i just want to make one or two parts.

I have been playing around with making silicone parts with 3D printer moulds. I used some soft shore 0030 silicone and made a few parts. The process seems to work very well. My idea is to make a 3D printed negative mould and then inject silicone to make the keyboard. Finally when the part is made, i just need to very precisely cut aluminum foil in the shape of the bottom bridging contacts and stick it with adhesive.

How much of a crackpot idea is this? I know it's pretty hard to stick anything to silicone that isn't silicone itself.

[SMTech]

Hellp all, hope you're doing well.

For the past few months i have been dabbling in mechanical design and 3D printing stuff. Anyway i was wondering if there's a way to make DIY membrane keyboards. Like the ones on TV remote controls and such. With those black conductive silicone bumps which bridge contact between two "fingers" on the PC board. I don't need volume, i just want to make one or two parts.

I have been playing around with making silicone parts with 3D printer moulds. I used some soft shore 0030 silicone and made a few parts. The process seems to work very well. My idea is to make a 3D printed negative mould and then inject silicone to make the keyboard. Finally when the part is made, i just need to very precisely cut aluminum foil in the shape of the bottom bridging contacts and stick it with adhesive.

How much of a crackpot idea is this? I know it's pretty hard to stick anything to silicone that isn't silicone itself.

Fairly silly. you can absolutely buy the rubber membrane and cut it up to suit your own arrangement. Underneath that what you typically find is called a tactile dome switch, this is a sprung dome shaped piece of metal and can be fitted to a PCB during the SMT process or glued into a membrane with adhesive glues. the dome is not stuck to the silicon. A fully DIY effort would probably have a very short life and very erratic peformance.

[BadeBhaiya]

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Fairly silly. you can absolutely buy the rubber membrane and cut it up to suit your own arrangement. Underneath that what you typically find is called a tactile dome switch, this is a sprung dome shaped piece of metal and can be fitted to a PCB during the SMT process or glued into a membrane with adhesive glues. the dome is not stuck to the silicon. A fully DIY effort would probably have a very short life and very erratic peformance.

I do know of those metal dome switches but they would require me to actually place the individual domes and reflow them. That isn't a problem itself but i want to make a keyboard of sorts for a portable device I'm planning with 85+ individual switches. That may get very tedious very quickly even if i want only two devices made. Plus dome switches cost money compared to just removing the soldermask on the board if I'm going with a silicone membrane keyboard. Welp getting the membrane is the hard part. I can't get anything commercially that isn't already in an existing product. All COTS membrane keypads are for 3x3 or 4x4 dialpad style uses.

I might just give this a go. Silicone, 3D printed mould everything together would still cost less than 50USD

[pastaclub]

Adafruit has ready-made silicone keypads (product# 1611). It's 4x4 square-shaped buttons and you can cut them apart if you want. They have a conductive carbon ring underneath for which you make a custom footprint. Sparkfun also has an almost identical product.

[cunningfellow]

I have been playing around with making silicone parts with 3D printer moulds. I used some soft shore 0030 silicone and made a few parts. The process seems to work very well. My idea is to make a 3D printed negative mould and then inject silicone to make the keyboard. Finally when the part is made, i just need to very precisely cut aluminum foil in the shape of the bottom bridging contacts and stick it with adhesive.

These are not membrane switches.  Membrane is where the button presses on two sheets of plastic with a 3rd sheet of plastic with holes as a spacer and the front and back sheet have conductive traces that touch.

I don't know about 3D printing a mold, but I mill molds out of renshape and then use soft silicone to make the main body.

Sticking aluminum foil will suck.  Instead get on aliexpress/ebay and buy "Conductive carbon pills" that are designed for the task.  You poke one down each hole in the mold and pour your liquid silicone on top.  The carbon impregnated silicone "pill" sticks to the fresh silicone as you would expect.

Don't make the holes for the carbon pads blind.  You will never get them out without tearing some.  Make then a stepped through hole.  You can then poke them out from the other side.

When I first started doing it maybe 10 or 15 years ago the hardest part was finding the carbon pills/pads.  I don't know why the Chinese sellers use the word pills but it makes it hard to find them amongst medication to reduce flatulence.

[cunningfellow]

oh - and there (at least) two different types sold on aliexpress for IR remote repair.

You have to get the ones that are little cylinders not the ones that are flat die cut stickers on a flat sheet.

I have also tried to mix up carbon in silicone to put into the holes and was messy and too hard to do.

I am sure the way things are going JLC_PCB will be offering a

"Full custom vulcanized silicone prototype rubber dome keyboard service 100mm x 100mm 5 pieces for $30"

in the next few months.

[cunningfellow]

And don't forget your fart channels