keypad.js

/**
 * Example of 4x4 membrane keypad reading (keypad directly wired on RasPi GPIO pins, not using I2C)
 * 
 * Setup :
 * - Hard : Raspberry Pi 4B, 16x2 LCD display behind PCF8574T, 4x4 membrane keypad
 * - Soft : command line utility 'raspi-gpio', Node v10+, Johnny-Five 1.4, Raspi-IO 11.0
 * 
 * Run: sudo node keypad.js
 */

const { Board, LCD, Pin, Buttons } = require("johnny-five");
const { RaspiIO } = require("raspi-io");
const { execSync } = require("child_process");
const utils = require("./utils");

const board = new Board({
  io: new RaspiIO(),
  repl: false
});

// warning: LCD must be wired to SDA1 & SCL1 pins for data transfer
// (instead of SDA0 & SCL0) otherwise it won't be recognized.
const lcd = new LCD({
  controller: "PCF8574T"
});

const pinCodes = {
  rows: ["GPIO5", "GPIO6", "GPIO13", "GPIO19"],
  cols: ["GPIO12", "GPIO16", "GPIO20", "GPIO21"]
};

const keys = [
  ["1", "2", "3", "A"],
  ["4", "5", "6", "B"],
  ["7", "8", "9", "C"],
  ["*", "0", "#", "D"],
];

var colPressed = null;
var rowPressed = null;

var keypad = { pins: null };

var cursorPos = 0;


board.on("ready", () => {
  
  lcd.clear().print("Waiting input").cursor(1, 0);
    
  // Start listening for key push
  checkCol();
  
  async function checkCol() {
    delete keypad.pins;
    
    keypad = {
      pins: Object.assign({}, pinCodes)
    };
    
    keypad.pins.rows = keypad.pins.rows.map(function (pinCode) {
      return new Pin({ mode: Pin.OUTPUT, pin: pinCode });
    });
    
    keypad.pins.cols = new Buttons(keypad.pins.cols.map(function (pinCode) {
      return { pin: pinCode, isPullup: true };
    }))
    
    keypad.pins.rows.forEach((pin) => { pin.low() });
    
    // required wait (for pin creation & pin.low() propagation?)
    await utils.sleep(50);
    
    keypad.pins.cols.on("down", function (button) {
      // send column index as parameter to checkRow()
      checkRow(pinCodes.cols.indexOf(button.pin))
    });
  }
  
  async function checkRow(numCol) {
    colPressed = numCol;
    
    // as soon as a button press on a column is detected,
    // inverse pins modes (input <=> output) to detect pressed button row
    keypad.pins.cols.forEach((pin) => { pin.removeAllListeners() });
    delete keypad.pins;
    
    keypad = {
      pins: Object.assign({}, pinCodes)
    };
    
    keypad.pins.rows = keypad.pins.rows.map(function (pinCode) {
      return new Pin({ mode: Pin.INPUT, pin: pinCode, type: "digital" });
    });

    // enable pullup resistors for input pins
    // I did not find a way to do it through Johnny Five ;
    // here we must use Pins instead of Buttons because an immediate read
    // (using Pin.query()) is required
    pinCodes.rows.forEach(function (code) {
      execSync('raspi-gpio set ' + parseInt(code.substring(4), 10) + ' pu');
    });

    keypad.pins.cols = keypad.pins.cols.map(function (pinCode) {
      return new Pin({ mode: Pin.OUTPUT, pin: pinCode, type: "digital" });
    });
    
    keypad.pins.cols.forEach((pin) => { pin.low() });
    
    // required wait (for pin creation & pin.low() propagation?)
    await utils.sleep(50);
    
    rowPressed = null;
    
    for(let currentRow = 0; currentRow < 4; currentRow++) {
      if (await isButtonPressedInKeypadRow(keypad, currentRow)) {
        rowPressed = currentRow;
        break;
      }
    }
    
    if (rowPressed !== null) {
      showKeyPressed();
    } else {
      console.log("Keypad issue: could not detect row of pressed key. Waiting for next key push.");
    }
    
    checkCol();
  }
  
  /**
   * Detect if a button has been pressed in specified keypad col
   * @return Promise
   */
  function isButtonPressedInKeypadRow(keypad, rowNum) {
    return new Promise((resolve) => {
      keypad.pins.rows[rowNum].query((state) => {
        resolve(state.value == 0);
      });
    });
  }
  
  function showKeyPressed() {
    let char = keys[rowPressed][colPressed];
    console.log("KEY PRESSED: ", char);
    if (cursorPos == 16) {
      cursorPos = 0;
      lcd.clear();
    }
    lcd.print(char);
    cursorPos++;
  }
});

package.json

{
  "name": "keypad-example",
  "version": "1.0.0",
  "description": "Example of 4x4 membrane keypad reading",
  "main": "keypad.js",
  "scripts": {
    "test": "echo \"Error: no test specified\" && exit 1"
  },
  "author": "Maxime Pacary <maxime.pacary@gmail.com>",
  "license": "MIT",
  "dependencies": {
    "johnny-five": "^1.4.0",
    "raspi-io": "^11.0.0"
  }
}

utils.js

module.exports = {
  sleep: function(ms) {
    return new Promise((resolve) => {
      setTimeout(resolve, ms);
    });
  }
};