jkinkennon

The 500ms timeout seems about 10x too long as I'm using 50ms pulses successfully, though on higher voltage SAMs. If anything is slowing down the MIDI communications then it's possible that you are bouncing the SAMs sufficiently that they actually do switch back on for a moment and cause the fluttering. I realize the 500ms timeout is there as a safety precaution and shouldn't be coming into play of course. Also, the inputs from the SAMs need to be as well debounced as you would do for keys. I assume that's the case. Sorry, I'm not totally up to speed on your hardware but am offering some advice based on similar projects. I like Pete's last advice as well having recently fought with a couple of "spooky" matrix issues myself.

One more thought about your DIN and DOUT configs for a matrix. I'm running a similar matrix circuit for my Allen 603-D midification project. I just experienced "extra" notes when I connected my pedal matrix. The pedals have longer ribbon cables so I put the scope on the inputs (similar to your DIN config) and found that the combination of operating speed and increased cable capacitance was too much for the 10k pullups to deal with. Basically the rise time of the signal was slow enough that the voltage was at an indeterminate value when the next column was driven. So I'm swapping the 10k's for 4.7k and if that doesn't cure the problem then I'll slow the circuit a bit.

John, I hadn't been following the entire chain of events leading to your related post about the DOUT to DIN connection. I wouldn't recommend using a ULN 2803 driver chip on the DOUT as that will leave all the matrix columns in a high impedance state when they are not being driven. I don't know that the drivers wouldn't work, but they are not needed. When the diodes are not biased off by a positive voltage on the matrix column they are subject to coupling unwanted noise pickup to the DIN inputs.

Hi Johnc, There's nothing inherently wrong, in fact it's better to not have the 220 ohm resistor in the circuit. If you've lost more than one IC then something is going wrong for sure. I'd first check that the 10k pullups are correctly installed on the DINs and are working, that is the 74HC165 inputs are staying at about 5v when no keys are pressed. If that checks out I'd be thinking of watching the signals on an o-scope to be sure there are clean "square" transitions and that inputs aren't spending too much time at intemediate values between 0 and +5v. Long cables with high capacitance might be an issue. Certainly you want to be sure the +5v is hooked up on the DIN and DOUT and that each chip has the little rf bypass cap installed {the .01 or .001 capacitor).