I have some 4x4 silicone keypads from Sparkfun, which I bought in 2007. I never finished the project, and I am picking it back up now. It’s for a monome 40h (64 button midi interface).
However, I’m experiencing problems registering key presses on the pcb, and I’m trying to troubleshoot. I have tried cleaning the old pcb (which I etched myself, in 2007) with isopropanol, and I have measured the conductive ring under the keys with a DMM (ohmmeter). It measures a resistance of 500ohm around the ring.
Is that a problematic high value, which could be causing bad connection? I have to press hard on the key, and wiggle it, to register a button event. Do the keys/rings get bad with age? Alternatively, it could of course be my pcb. The copper traces were tinned immediately after development, but maybe this still oxidizes badly.
It sounds like the pcb button pads never were tested and might have had a resistive coating all along. They could have picked up a haze in the time since, too. The meter probes can pierce it but the rubber contact pads lay over the top. I’d give one a nice burnishing and perhaps test with some other donor contact/keypads scavenged from old tv remotes or calculators, etc.
Thanks for replying, good advice!
Perhaps if someone has the same keys from sparkfun they might measure the resistance (dmm between two points equally spaced around the circle) for me to compare? Seems to me 500ohm is a bit high
I will try to measure some old remote controls for comparison, that is a great idea
Maybe! I certainly don’t have on to test with but someone might…fingers crossed!
On the flip-side of things you could probably just get a revamped/new version of this whipped up on jlcpcb or similar pretty quick (and perhaps grab some new buttons?)
On second look, those buttons might be closer in size & grid to a touchtone dial telephone keypad* and a lot of households have armloads of disused phones for cutting up with scissors.
*4 bonus points in the Game of Anachronistic Redundancies Game
