4 ms·

Not sure if the author of the post is around, but I guess this is a question for anyone who has designed keyboards: have you ever tried using shift registers fo

Not sure if the author of the post is around, but I guess this is a question for anyone who has designed keyboards: have you ever tried using shift registers for reading all the keyswitch inputs, and is it worth it? Does it mean you don't have to use a diode per switch? I've designed my own as well but just went with the traditional key matrix with a diode per switch. Works well enough for the current size. https://github.com/bschwind/key-ripper https://github.com/bschwind/key-ripper

mzzter 4y ago
Last time i researched adding shift registers was over a year ago and I didn’t find many examples (I vaguely recall one possibly with qmk), and very little public discussion besides a reddit question. Popular guides like ai03’s at the time recommended upgrading to a microcontroller with more gpio before introducing shift registers. Searching again, looks like zmk added support for the common 595 shift register: https://github.com/zmkfirmware/zmk/pull/1325 https://github.com/zmkfirmware/zmk/pull/1325 Edit: You could avoid using diodes, but diodes increase the number of switches possible via a matrix more than shift registers do by giving you more gpio. I’d imagine one can use both together.
gmbuell 4y ago
This kind of thing is really common in the DIY synthesizer world. Here's a great resource: http://www.openmusiclabs.com/learning/digital/input-matrix-scanning/index.html http://www.openmusiclabs.com/learning/digital/input-matrix-s...
riskable 4y ago
My analog keyboards use analog multiplexers (74HC4067) which is similar to how shift registers work. Except they're full of flip-flops (2-way) instead of digital logic. I made two videos talking about how I design my analog keyboard PCBs and how I'm using analog multiplexers here: https://youtu.be/TfKz_FbZWLQ https://youtu.be/TfKz_FbZWLQ
jsmith45 4y ago
Shift registers are an interesting option. They are obviously feasible, especially if using ones with a built in pull-down. They do avoid having a diode per key, in exchange for needing a chip for N keys, where n is the number of of parallel inputs in your parallel to serial shift register. They can also save IO lines. Obviously with if using chainable shift registers, you can have an unlimited number of keys with just 3 IO lines. More realistic of course, would be to use several IO lines in parallel. For a 64 key matrix, one could say use 8, 8-bit shift registers, each connected to one input line, plus one output latch line and one output clock line (for a total of 10), vs the 16 lines needed traditional matrix. 8 input lines is nice, because if you pick the I/O lines right, retrieving the values is just a single port read. Making the procedure: latch, (toggle clock twice, read port, write to next location in memory buffer) x8. There are of course downsides, like shift registers needing more board space than tiny surface mount diodes, but this is not necessarily a deal-killer.

mzzter 4y ago

Last time i researched adding shift registers was over a year ago and I didn’t find many examples (I vaguely recall one possibly with qmk), and very little public discussion besides a reddit question. Popular guides like ai03’s at the time recommended upgrading to a microcontroller with more gpio before introducing shift registers. Searching again, looks like zmk added support for the common 595 shift register: https://github.com/zmkfirmware/zmk/pull/1325 https://github.com/zmkfirmware/zmk/pull/1325 Edit: You could avoid using diodes, but diodes increase the number of switches possible via a matrix more than shift registers do by giving you more gpio. I’d imagine one can use both together.

gmbuell 4y ago

This kind of thing is really common in the DIY synthesizer world. Here's a great resource: http://www.openmusiclabs.com/learning/digital/input-matrix-scanning/index.html http://www.openmusiclabs.com/learning/digital/input-matrix-s...

riskable 4y ago

My analog keyboards use analog multiplexers (74HC4067) which is similar to how shift registers work. Except they're full of flip-flops (2-way) instead of digital logic. I made two videos talking about how I design my analog keyboard PCBs and how I'm using analog multiplexers here: https://youtu.be/TfKz_FbZWLQ https://youtu.be/TfKz_FbZWLQ

jsmith45 4y ago

Shift registers are an interesting option. They are obviously feasible, especially if using ones with a built in pull-down. They do avoid having a diode per key, in exchange for needing a chip for N keys, where n is the number of of parallel inputs in your parallel to serial shift register. They can also save IO lines. Obviously with if using chainable shift registers, you can have an unlimited number of keys with just 3 IO lines. More realistic of course, would be to use several IO lines in parallel. For a 64 key matrix, one could say use 8, 8-bit shift registers, each connected to one input line, plus one output latch line and one output clock line (for a total of 10), vs the 16 lines needed traditional matrix. 8 input lines is nice, because if you pick the I/O lines right, retrieving the values is just a single port read. Making the procedure: latch, (toggle clock twice, read port, write to next location in memory buffer) x8. There are of course downsides, like shift registers needing more board space than tiny surface mount diodes, but this is not necessarily a deal-killer.