Keyboard Matrix, MIOS / MIDIO128?

[jtadams]

Hi all! In further analyzing the ability to MIDIfy an old Allen MOS-1 console in-place, i.e. without dismantling the existing electronics, I realized it is using some form of keyboard diode switch matrix. Hence the following questions. I apologize if this is already documented somewhere, but I did look around and did not find any answers. I'm somewhat familiar with electronics and with the design of the DIN module, but not with the details of the Allen design nor with MIOS or MIDIO128.

1. Can I assume that the existing electronics are polling the matrix and that I can determine whether a key is pressed by performing a logical XOR against the two inputs representing the two switch contacts? (If a key is pressed at any given moment in time, thus closing the switch, then both voltages must be high, or both must be low, at least if I'm understanding correctly.)

2. I understand that MIOS can poll a DIN module once each millisecond . . . won't the probability of the existing organ's scan rate being much higher make this too slow? (I assume it is a supersonic frequency, so as to avoid interfering with the actual signal, and if so then the state of these pins will change many times within that millisecond.)

3. Is there any functionality already in MIOS and/or MIDIO128 that I'm somehow missing that would allow me to interact with the keyboard matrix?

4. Is there an easy way to scan the matrix if the organ is turned off, without any risk of damaging the existing electronics? (I wouldn't think so since we'd have to apply some voltage to one side of the diode array in order to read the outputs and I have no idea what effect that would have on the organ's electronics, but again maybe I'm missing something.)

Thanks!

[baptistou]

Hi,

Most of the time in a swich matrix you apply a voltage on a row and check wich swich is closed in the column (or the opposite). The buttons in a column are all connected to the same input on the electronic system. That way you apply the voltage on one single row at a time, thus selecting wich buttons will be active, you get their state and you go on with the nex row and so on.

I doubt that it is as you say one button closes two swiches.

I haven't done that with a midibox but I know that many other people do so that must not be that complicated to handle.

I don't know if you can go faster than 1ms per row but that should be enough anyways.

The functionnality you are looking for is probably "blm" (button led matrix), have a look at the examples for mios8 or mios32.

I guess that you'll need to do something to separate your keyboard electronics from the midibox's ones

Baptistou