Help: Multiple problems with project

Question

So I'm making a small piano project (with or without Mozzi library) using Arduino UNO or Pro Mini for the class (as a part of STEM education we are having here), but I have encountered some issues:

I can't figure out how to read 13 keys (single octave C~B, and black keys) without freezing the tone every time key is being read or restarting the waveform each time the function is called.
Using resistor array worked, but its tone drifted too much for the kit and it only allowed one tone to play even with multi-key polyphony code. Now I divided the button into four sections shown below (in image) to try to minimize pitch drift, but now I have to read 4 analog input (or 3 if I omit second octave C and don't use 13th button)
Since Arduino's built-in Tone function only has single tone and there is no way around it (and you know how awful single tone synth sounds when it outputs pure PWM straight into that tiny Mylar speaker), we attempted to use Mozzi because it supports FM and sine output through PWM (and some LP filter if it's absolutely necessary), a sound synthesis library. But then I have to rewrite the entire code. (The code I used is lifted straight from https://www.arduino.cc/en/Tutorial/toneKeyboard) Could somebody help me a bit? It does not have to sound absolutely beautiful (basic waveforms are just fine) and it just has to have at least two-note polyphony.

Any help is appreciated!

p.s. Values of resistors on buttons (except for pull-down resistors) are placeholders.

Actual values from left to right on each row are: 4.7K, 1K, 470R, 100R

ntewinkel · Answer

For reading the keys, have you tried the Arduino Keypad library?

https://playground.arduino.cc/Code/Keypad

Their example only shows 12, but I see you can purchase keypads with 16. Or more likely you can probably hook up your piano keys in a similar circuit.

edit: The keypad tutorial shows more on how to use it, including the detail that the circuit is basically rows and columns of buttons connected to pins for rows and pins for columns. Physically you can of course make it one straight line, but to get your 13 keys you need 4x4 = 8 pins to get 16 possible buttons.

https://playground.arduino.cc/Main/KeypadTutorial

Cheers,

-Nico

pathfider1998 · Answer

Currently, I got everything nailed down to produce perfect value every time button is pressed if Keypad library cannot be used.

C: 0 0 0 706

C#: 0 0 705 0

D: 0 705 0 0

D#: 705 0 0 0

E: 0 0 0 330

F: 0 0 330 0

F#: 0 330 0 0

G: 330 0 0 0

G#: 0 0 0 186

A: 0 0 186 0

A#: 0 186 0 0

B: 186 0 0 0

C: 0 0 0 44 (Limit for 12-key implementation)

C#: 0 0 44 0

D: 0 44 0 0

D#: 44 0 0 0

Using following code:

void setup() {

Serial.begin(9600);

}

void loop() {

int sensorValuea = analogRead(A0);

int sensorValueb = analogRead(A1);

int sensorValuec = analogRead(A2);

int sensorValued = analogRead(A3);

Serial.print("Line 1: ");

Serial.print(sensorValuea);

Serial.print(", ");

Serial.print("Line 2: ");

Serial.print(sensorValueb);

Serial.print(", ");

Serial.print("Line 3: ");

Serial.print(sensorValuec);

Serial.print(", ");

Serial.print("Line 4: ");

Serial.print(sensorValued);

Serial.println(". ");

delay(10);

}

This is the requirement for the code:

Be able to read multiple buttons, doesn't matter if it's one of each group of buttons or individually, within 6 analog pins (and 9 digital pins except 9, 10 and/or 11) limit (I will be using the layout from 4x4 button board)
Preferably no shift registers, but it can be used if it's absolutely required
Be able to produce at least two-tone polyphony
Optionally use Mozzi library to generate sound, waveform really doesn't matter, be it FM synth or just basic waveform with fixed ADSL setting
Sound should not restart while button is held down (just like any digital pianos)
Sound does not have to stop exactly when the key is released, it just has to end before 30ms

Help: Multiple problems with project

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