I took out this 3 octave keyboard from some electric keys I found.
First thing I should like to do is to read the pressing of those keys with Arduino. How should I do so?
The keys looks like this:
What model of Arduino?
You are going to need 18 digital pins.
Remember on Uno and some other models, you cannot use pins 0, 1.
how come only 18 if I have 36 keys?
for testing I will use Uno, but eventually it will be nano. I could use multiplexer CD74HC4067?
In order to connect the keyboard to an Arduino and read keypresses you need to know how its keys are wired
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is there a way to check it with a multimeter?
Do you have a multimeter or a breadboard and some LEDs & resistors? The first thing you are going to need to figure out is how the keyboard is wired internally, and what the purpose of each of the pins on the J1 & J2 connectors is. Then you can draw a schematic showing how everything is connected (the schematic doesn't need to show every individual key, just enough to give understanding.
With that knowledge, and an extra chip such as a multiplexer chip or shift register, it will be possible to reduce the number of Arduino pins required.
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The keys will be connected as a matrix. I count 37 keys?
There might be two switches inside each key, to detect how hard or fast it was pressed. EDIT: yes, I can see 74 diodes, so there must be 2 switches per key I think.
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Q: Was the keyboard touch sensitive?
I pretty sure it was. I think it had also potentiometer that is returning to the middle position and another regular one that will stay at place.
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@alexxjohn if @hk_jh had wanted an AI answer, I'm sure they could have used GhatGPT or similar themselves.
EDIT: that post seems to have vanished.
No, there's another one you missed! 10-way
That was probably to shift the frequency, max ± one note
no, there is also J2 with 10 pins
All the diodes suggest that somehow there is a matrix involved.
A pitch bend and a modulation ?
probably not i guess, there appears to be no circuitry for doing that.
Oh well in that case it may be touch sensitive, but how that was implemented ??
A normal system could use a capacitor that is charged between the 1st and 2nd switch being pressed, but a resistor would be required for that.
There may also just be 2 diodes per key.
I think you may anyway need to take it apart a bit further and it might be easier to just trace the PCB.
A LED + current limiting resistor may be more practical with the diodes and all, but first i think i would remove the screws above the keys and see if that removes the keys, and then the screw that mount the PCB onto the keys and see what i find.
Do you know the brand/model number, the schematic may be available online.
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I understand the usual way is to time the delay between the first & second switches closing, for the same key. That will require some pretty fast scanning of the matrix!
right - need better glasses :)
So my "money" is on this :
Tthere are 36 keys and each key has two contacts, so there are 72 independent switch closures. Each closure is diode-isolated, which accounts for 72 of the 74 diodes and hints at a matrix designed to avoid ghosting during multiple simultaneous presses.
With 10+8 signal lines across the two connectors, the most consistent topology is a scanned matrix, most likely 8 × 10, providing 80 intersections. Of these, 72 are populated for the dual-contact velocity-sensitive keys and there are a couple remaining ones (the extra 2 diodes) for something else. As the keyboard is small, possibly the two remaining diodes were assigned to an octave shift through a plus and minus buttons but could also for a sustain pedal and a momentary button ?
In such designs, each key closes two switches at slightly different travel depths and indeed the controller measures the time difference between the first and second contact closures to compute velocity.
time to play with the DMM indeed.
Maybe I also need better glasses, because I counted 37 keys, which would explain the 74 diodes.
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