I have attached a 3x4 keypad to my Arduino Leonardo as an input method. Whenever I press the buttons, the majority of the keys work but specific ones don't. Here's my code, I've set it up to beep a piezo buzzer when it gets a keypress.

#include <Keypad.h>

int buzzerPin = 0;
const byte ROWS = 4; //four rows
const byte COLS = 3; //three columns
char keys[ROWS][COLS] = {
byte rowPins[ROWS] = {12, 13, 8, 10}; //connect to the row pinouts of the keypad
byte colPins[COLS] = {11, 7, 9}; //connect to the column pinouts of the keypad

Keypad keypad = Keypad(makeKeymap(keys), rowPins, colPins, ROWS, COLS);

void setup(){
    pinMode(buzzerPin, OUTPUT); //Set buzzerPin as output
    keypad.addEventListener(keypadEvent); //Add an event listener for the KeyPad

void loop(){
    char key = keypad.getKey();

void keypadEvent(KeypadEvent eKey) {
        // When the KeyPad will be pressed, the results will appear on the serial monitor.
        switch (keypad.getState()) {
        case PRESSED:
                Serial.print("Enter: ");

void beep(unsigned char delayms) { //creating function
    tone(buzzerPin, 2000); //Setting pin to high
    delay(delayms); //Delaying
    noTone(buzzerPin); //Setting pin to LOW
    delay(delayms); //Delaying

I based my rows/columns off of this pin-out: https://www.jaycar.com.au/12-key-numeric-keypad/p/SP0770, but I later found out some of the columns had to be swapped :P

Here's a diagram of what's happening: Diagram of working and not working keys

The keys in red do not work.

I wouldn't have posted this on stack exchange but it looks like an oddly specific pattern, and no matter what I changed, it didn't work.

(And yes, that is the exact keypad I bought from Jaycar)

Edit: I forgot to mention that I was using a prototype shield to plug the keypad into, but all pins are confirmed working on that.

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  • 2
    If either row #2 or column #2 is used it does not work, unless both are used. Have you exchanged/mixed row #2 and column #2 somehow? There must be some logic in it. Can you disconnect the keypad and test every button with a multimeter? Please tell which arduino pins are connected to which keypad pins. – Jot Sep 9 '18 at 10:22
  • One more question: is it a cheap clone board? Because row #2 is connected to pin 13. The official arduino leonardo has a extra logic chip, so pin 13 can be used as a input without problem. Try to use another pin for row #2. Update your question with the extra information. – Jot Sep 9 '18 at 10:34
  • Agree w/@Jot, row #2 is swapped w/column #2. Try changing your code to read "byte rowPins[ROWS] = {12, 7, 8, 10}; //connect to the row pinouts of the keypad byte colPins[COLS] = {11, 13, 9}; //connect to the column pinouts of the keypad" to see if a code change can clear up the problem. – st2000 Sep 9 '18 at 23:04
  • are you sure that 5 actually works? – jsotola Sep 10 '18 at 0:43
  • Right so I've figured it out now (thanks to you guys), it turns out that yes in fact row 2 and column 2 were swapped around. I also forgot to mention that this was a prototype shield I was plugging the pins into, but thanks everyone for the quick and useful replies. In terms of marking this question as answered, I'm fairly new to this... Do I just quote one of you above in my answer button? Or do I requrie a moderator or something? – Neonalig Sep 10 '18 at 9:49

A row against a row does not work, or a column against a colum.
That means there is a logical explanation. Row #2 is swapped with column #2.
Button 5 does work, because that still has a row against a column (but then the other way around).

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