Solutions for a very high number of inputs

Question

I have a rather ambitious project to get started learning about microcontrollers and embedded systems. I have cheaply acquired an old organ console that is currently analog that i want to convert to digital/MIDI. The MIDI out part seems straightforward enough from a bit of Google searching, but I have no idea how to deal with the seemingly massive number of inputs I need. The current console is wired with a common rail that spans each keyboard, voice bank, etc., then each key is individually wired. The straightforward approach to this would seem to indicate that I need 300+ input connections. I understand the concept of shift registers for pulling in all of those lines, but I'm worried about being able to read them fast enough to get me the nearly real-time response I need to make it a usable musical instrument. Thoughts?

michaelkellett · Answer

It's not so hard, I'll assume that 1mS latency is good enough, so you need a 300kHz clock on your shift register, and thats assuming that you use just one serial stream for all your inputs. A bigger problem will be wiring it all up, if I were doing this I would design a little board with about 32 inputs (using a 64 pin micro) and put these where physically convenient to reduce the amount of wire. Then link the little boards to a cenrtal controller using CAN, RS485, or whatever you prefer. An STM32F100R4T6B is £1.98 from farnell, has 64 pins so will give you 32 inputs and a serial link with no need for shift registers. You'll need to design a board but its not too hard. Let me know if you fancy going this way and I might be able to help a bit more. MK

Solutions for a very high number of inputs

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