Giovanni Carrera
Published © GPL3+

Only Three Pins for a 4x3 Keypad

A technique for drastically reducing the pins required by a matrix keypad is described.

BeginnerFull instructions provided1 hour4,982
Only Three Pins for a 4x3 Keypad

Things used in this project

Hardware components

Resistor 330 ohm
Resistor 330 ohm
×1
Resistor 1k ohm
Resistor 1k ohm
×3
Resistor 3k ohm
×1
4x3 matrix 12 key array switch keypad
×1
Arduino UNO & Genuino UNO
Arduino UNO & Genuino UNO
×1

Software apps and online services

Arduino IDE
Arduino IDE

Hand tools and fabrication machines

Soldering iron (generic)
Soldering iron (generic)

Story

Read more

Schematics

Keypad wiring diagram

Code

Analog4x3Keybf.ino

Arduino
Simple program to test KeyPad() function
/* program Analog4x3Keybf
 *  test for 4x3 keys keyboard with 3 analog outs
 *  G. Carrera - 19/11/2018
 */

// limits of keyboard output values:
const int NADCm100[4] = {923,669,412,156};
const int NADCp100[4] = {1123,869,612,356};
const char key[13] = {'1','4','7','C','2','5','8','0','3','6','9','E'};
int keyval[3];
int i,colp,val;


void setup(){
 Serial.begin(9600); // used with serial monitor
}

void loop() {
  char k;
  k = KeyPad();// read keypad
  if (k != 'N'){ // a key was pressed
          Serial.print("key = ");
          Serial.println(k);
          delay(500);
  }
}

/******** Functions used by program ********/
char KeyPad(){
// read keypad and return the char key
// key = 'N' for none
  KeyScan();// read analog keyboard
  if (keyval[0]+keyval[1]+keyval[2] < 40) {
    return 'N';
  }
  else { // a key was pressed
    delay(10);// antibounce
    KeyScan();// reread analog keyboard
    for (i=0; i < 3; i++){//identify which column it belongs to
      if (keyval[i] > 40){
        colp= i;
        val= keyval[i];// this is the corresponding value
        for (int j=0; j < 4; j++){// identify which key was pressed on the column
          if (val >= NADCm100[j] && keyval <= NADCp100[j]){ 
            return key[colp*4+j];
            break;
          }
        }
      }  
    }
  }
}


void KeyScan(){// read analog keyboard
  keyval[0]= analogRead(A0);
  delay(1);
  keyval[1]= analogRead(A1);
  delay(1);
  keyval[2]= analogRead(A2);
  delay(1);  
}

Credits

Giovanni Carrera

Giovanni Carrera

13 projects • 35 followers
Electronic Engineer

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