Interfacing 422 button inputs

Hi Folks,

I am trying to build a MIDI keyboard with arduino UNO similar to tonal plexus. Here, I need to interface 422 button inputs in which 211 for octave one and the remaining 211 to octave two. I am unsure how many multiplexers i should use or any other cost effective ways will be helpful rather than expanding footprint of the device i am building. Please, kindly shed some suggestions in help building me this project

Best Regards,
Harish

You are going to have to do a lot of wiring then!

To interface large numbers of button inputs - a PC keyboard is a good example - you wire them in an array. As you will most likely have more than one pressed simultaneously, each button at a matrix cross point will require a series diode. It may however be more practical to break them up into matrix groups of 64 or 80 since 64 is 8 by 8 or 80 is 8 by 10 and there are chips with those number of connections.

Actually, a better idea - use a number of these PCF8575 expander boards.

Three of them to be precise - they share the I2C bus, there are address jumpers on the back giving four address options - one as a one-of-16 driver pulling down a matrix line at a time, and the other two reading 32 matrix columns for up to 512 buttons/ switches. And you definitely still need the diodes.