arduino keyboard scanner

maudio49.ino

#include "MIDIUSB.h"

bool debug = 0;
int maxPressTime = 250;
int minVelocity = 10;
int maxVelocity = 90;
int midiChannel = 0;

int keys[98] = {
  31, 29,
  56, 59,
  80, 83,
  104, 107,
  92, 95,
  68, 71,
  44, 47,
  8, 11,
  20, 23,
  58, 57,
  82, 81,
  106, 105,
  94, 93,
  70, 69,
  46, 45,
  10, 9,
  22, 21,
  48, 51,
  72, 75,
  96, 99,
  84, 87,
  60, 63,
  36, 39,
  0, 3,
  12, 15,
  50, 49,
  74, 73,
  98, 97,
  86, 85,
  62, 61,
  38, 37,
  2, 1,
  14, 13,
  55, 53,
  79, 77,
  103, 101,
  91, 89,
  67, 65,
  43, 41,
  7, 5,
  19, 17,
  54, 52,
  78, 76,
  102, 100,
  90, 88,
  66, 64,
  42, 40,
  6, 4,
  18, 16
};

unsigned long pressStart[49] = {};


bool pressed[49] = {};

void setup() {
  Serial.begin(9600);
  //select pins
  // ABC of INPUT
  pinMode(10, OUTPUT);
  pinMode(11, OUTPUT);
  pinMode(12, OUTPUT);
  // ABC of OUTPUTs
  pinMode(2, OUTPUT);
  pinMode(3, OUTPUT);
  pinMode(4, OUTPUT);
  // from keyboard (9 pin)
  pinMode(5, INPUT); // gray
  digitalWrite(5, HIGH); // pullup
  pinMode(6, INPUT); // yellow
  digitalWrite(6, HIGH); // pullup
  // to keyboard (12 pin)
  pinMode(7, OUTPUT); // green
  pinMode(8, OUTPUT); // green
}

void set4051(int pinA, int pinB, int pinC, int channel) {
  // A = least significant bit
  // bitRead also starts from least significant bit
  digitalWrite(pinA, bitRead(channel, 0));
  digitalWrite(pinB, bitRead(channel, 1));
  digitalWrite(pinC, bitRead(channel, 2));
}

void loop() {
  for (int n = 0; n < 98; n++) {
    int k = keys[n];
    // for finding out order of keys, comment out above line and rename n to k
    int i = k / 12;
    int o = k % 12;
    int readPin = bitRead(i, 3) == 0 ? 6 : 5;
    set4051(10, 11, 12, i);
    set4051(2, 3, 4, o);
    digitalWrite(7, bitRead(o, 3));
    digitalWrite(8, !bitRead(o, 3));
    bool isConnected = digitalRead(readPin) == LOW;
    bool isDown = n % 2 == 1;
    int keyIndex = n / 2;
    int midi = keyIndex + 38;
    bool isPressed = pressed[keyIndex] == 1;

    // keypress starts
    if (isConnected && !isPressed && !isDown && !pressStart[keyIndex]) {
      if (debug) {
        Serial.print("start pressing ");
      }
      pressStart[keyIndex] = millis();
    }

    // key is now fully pressed
    if (isConnected && !isPressed && isDown) {
      unsigned long pressTime = millis() - pressStart[keyIndex];
      float f = (1 - (float)pressTime / (float)maxPressTime);
      int velocity = f * (maxVelocity - minVelocity) + minVelocity;
      if (debug) {
        Serial.print("done pressing ");
        Serial.println(f);
      }
      pressed[keyIndex] = 1;
      if (pressTime <= maxPressTime) { // min velocity?
        noteOn(midiChannel, midi, velocity);
        MidiUSB.flush();
        if (debug) {
          Serial.print("on ");
          Serial.print(midi);
          Serial.println(" ");
        }
      }
    }
    // key is now fully unpressed
    if (!isConnected && isPressed && !isDown) {
      pressed[keyIndex] = 0;
      noteOff(midiChannel, midi, 0);
      MidiUSB.flush();
      if (debug) {
        Serial.print("off ");
        Serial.print(midi);
        Serial.print(" ");
        Serial.println(" ");
      }
    }
    // key is unpressed => may include keypresses that have started but did not go down
    if (!isConnected && !isDown) {
      pressStart[keyIndex] = 0; // reset time when key is released completely
    }
  }
}

void noteOn(byte channel, byte pitch, byte velocity) {
  midiEventPacket_t noteOn = {0x09, 0x90 | channel, pitch, velocity};
  MidiUSB.sendMIDI(noteOn);
}

void noteOff(byte channel, byte pitch, byte velocity) {
  midiEventPacket_t noteOff = {0x08, 0x80 | channel, pitch, velocity};
  MidiUSB.sendMIDI(noteOff);
}

Thanks for dissecting your keyboard and sharing your findings with us. I have been wanting to make a midi keybed for some time, 3d printing the keys and designing my own pcbs which I’ll get JLBPCB to make for me. The only things that has kept me back is finding a suitable keyboard scanner circuit. I have drawn out your scanner circuit in Kicad as best as I could following your sketch. I wasn’t sure if there should be a diode from X4 of the first 4051 to X3 on the last 4051, and I wasn’t sure about arduino pins 10,11 and 12 going to keyboard pins 2,3 and 4. If you could advise me here, I’d be most grateful. I won’t dive straight into assembly, I’m going to play around with the Leonardo and the multiplexers for a while to get used to them first. Thanks.

Oh just one observation that I had, I see that you used your ninth input pin, purely for the first key. I am going to use just 8 input pins and make a 48-note keyboard. Obviously I’ll have to find all the key values again but that should be a problem.

@jasper192
hey glad you got something out of it. i don't remember all the details but this drawing should be what i did, so arduino pins 10 11 12 go to the upper 4051 into the 3 pins on its bottom right. you can also see it on the photo. i don't remember using any diodes. but take all this with caution, as i am not an expert and this was just me tinkering around, finding something that worked

Yeah thats the one I used. I’m an engineer so might go back to basics and use an arduino with lots of pins to creat the matrix, cutting out the multiplexer. That would in turn simplify the software. Cheers mate

…

On Mon, 16 Feb 2026 at 13:06, felixroos ***@***.***> wrote: ***@***.**** commented on this gist. ------------------------------ @jasper192 <https://github.com/jasper192> hey glad you got something out of it. i don't remember all the details but this drawing <https://loophole-letters.vercel.app/img/maudio49/scanner-schematic.png> should be what i did, so arduino pins 10 11 12 go to the upper 4051 into the 3 pins on its bottom right. you can also see it on the photo <https://loophole-letters.vercel.app/img/maudio49/arduino-scanner-pcb.png>. i don't remember using any diodes. but take all this with caution, as i am not an expert and this was just me tinkering around, finding something that worked — Reply to this email directly, view it on GitHub <https://gist.github.com/felixroos/cd7111d1b1a2ba7e381b82faf6abb9e2#gistcomment-5989280> or unsubscribe <https://github.com/notifications/unsubscribe-auth/BKMEZJ6QWDWPME5K3KDTX6T4MGXF7BFHORZGSZ3HMVZKM5LQMRQXIZNMON2WE2TFMN2F65DZOBS2WR3JON2EG33NNVSW45FGORXXA2LDOOIYFJDUPFYGLJDHNFZXJJLWMFWHKZNJGEYDOOJSG42TQMVKMF2HI4TJMJ2XIZLTSOBKK5TBNR2WLKBRGIYDEMZQGMZKI3TBNVS2QYLDORXXEX3JMSBKK5TBNR2WLJDUOJ2WLJDOMFWWLO3UNBZGKYLEL5YGC4TUNFRWS4DBNZ2F6YLDORUXM2LUPGBKK5TBNR2WLJDHNFZXJJDOMFWWLK3UNBZGKYLEL52HS4DF> . You are receiving this email because you were mentioned. Triage notifications on the go with GitHub Mobile for iOS <https://apps.apple.com/app/apple-store/id1477376905?ct=notification-email&mt=8&pt=524675> or Android <https://play.google.com/store/apps/details?id=com.github.android&referrer=utm_campaign%3Dnotification-email%26utm_medium%3Demail%26utm_source%3Dgithub> .