Arduino Keyboard code
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This is the code for the Arduino keyboard that will send a differenc character using the UART serial port each time we press a new button. The code is simple. You will need the Adafruit_Keypad as well so download the .zip file from below and install it to your Arduino IDE. Upload the code to the PCB adn test it out with the serial monitor or an external LCD to see the sent character. Download the code or copy it from below.








schematic Arduino keyboard homemade DIY



/* This is the code for the Arduino keyboard I've made, ELECTRONOOBS 21/08/2019
 *  Tutorial: https://electronoobs.com/eng_arduino_tut103.php
 *  Schematic: https://electronoobs.com/eng_arduino_tut103_sch1.php
 *  Code: https://electronoobs.com/eng_arduino_tut103_code1.php
 *  PCB GERBERs: https://electronoobs.com/eng_arduino_tut103_gerber1.php
 *  YouTube channel: https://www.youtube.com/channel/UCjiVhIvGmRZixSzupD0sS9Q
 * 
 *  Connect Rx and Tx to any other microcontroller and use serial at 115200 bauds.*/


#include "Adafruit_Keypad.h"                          //Downlaod here: https://electronoobs.com/eng_Arduino_Adafruit_Keypad.php
const byte ROWS = 4;  // rows
const byte COLS = 10; // columns
//define the symbols on the buttons of the keypads
char keys[ROWS][COLS] = {
  {'1','2','3','4','5','6','7','8','9','0'},
  {'q','w','e','r','t','y','u','i','o','p'},
  {'a','s','d','f','g','h','j','k','l','!'},
  {'*','-','z','x','c','v','b','n','m',','}   //SHIFT = * // OK = - // RETURN = ! // SPACE = ,
};

//Inputs/outputs
byte rowPins[ROWS] = {12, 13, A0, A1};                  //connect to the row pinouts of the keypad
byte colPins[COLS] = {2, 3, 4, 5, 6, 7, 8, 9, 10, 11};  //connect to the column pinouts of the keypad
int send_pin = A2;
int LED = A3;

//Variables
bool SHIFT = false;
bool send_pin_state = false;

//initialize an instance of class NewKeypad
Adafruit_Keypad customKeypad = Adafruit_Keypad( makeKeymap(keys), rowPins, colPins, ROWS, COLS);

void setup() {
  pinMode(send_pin,INPUT_PULLUP);
  Serial.begin(115200);           //If you change the speed here, the receiver Arduino will also need to change the speed. 
  customKeypad.begin();
  pinMode(LED, OUTPUT);
  digitalWrite(LED, SHIFT);
}

void loop() {
  
  /////////First we detect if send button was pressed//////////
  if(!digitalRead(send_pin) && !send_pin_state)
  {
    Serial.print("{");        //Send
    send_pin_state = true;
  }

  if(digitalRead(send_pin) && send_pin_state)
  {
    send_pin_state = false;
  }
  ////////////////////////////////////////////////////////////

  ///////Now detect when a keyboad button was pressed/////////
  ////////////////////////////////////////////////////////////
  customKeypad.tick();                      //Create the rows pulses

  while(customKeypad.available()){          //If a new push button was detected...
    keypadEvent e = customKeypad.read();    //Get what cahracter was pressed    
    if(e.bit.EVENT == KEY_JUST_PRESSED)     //Only send the character after we release that button in order to avoid problems...
    {
      if((char)e.bit.KEY == '*')            //If the character is "*", then we've presed the SHIFT key so we activate that variable
      {
        SHIFT = !SHIFT;                     //Enable/disable shift
        digitalWrite(LED, SHIFT);
      }
      
      else
      {
        if(SHIFT)                           //If shift is active we send special characters or UPERCASE
        {
          /////////////////Send special characters/////////////// 
          ///////////////////////////////////////////////////////
          if((char)e.bit.KEY == '1')
          {
            Serial.print("'");            
          }
          if((char)e.bit.KEY == '2')
          {
            Serial.print("@");            
          }
          if((char)e.bit.KEY == '3')
          {
            Serial.print(",");            
          }
          if((char)e.bit.KEY == '4')
          {
            Serial.print("$");            
          }
          if((char)e.bit.KEY == '5')
          {
            Serial.print("%");            
          }
          if((char)e.bit.KEY == '6')
          {
            Serial.print("?");            
          }  
          if((char)e.bit.KEY == '7')
          {
            Serial.print("!");            
          }   
          if((char)e.bit.KEY == '8')
          {
            Serial.print("&");            
          }
          if((char)e.bit.KEY == '9')
          {
            Serial.print("(");            
          }
          if((char)e.bit.KEY == '0')
          {
            Serial.print(")");            
          }
          /////////////////////////////////////////////////////// 
          ///////////////////////////////////////////////////////

          /////////////////Send UPERCASE first row/////////////// 
          ///////////////////////////////////////////////////////
          if((char)e.bit.KEY == 'q')
          {
            Serial.print("Q");            
          }
          if((char)e.bit.KEY == 'w')
          {
            Serial.print("W");            
          }
          if((char)e.bit.KEY == 'e')
          {
            Serial.print("E");            
          }
          if((char)e.bit.KEY == 'r')
          {
            Serial.print("R");            
          }
          if((char)e.bit.KEY == 't')
          {
            Serial.print("T");            
          }
          if((char)e.bit.KEY == 'y')
          {
            Serial.print("Y");            
          }  
          if((char)e.bit.KEY == 'u')
          {
            Serial.print("U");            
          }   
          if((char)e.bit.KEY == 'i')
          {
            Serial.print("I");            
          }
          if((char)e.bit.KEY == 'o')
          {
            Serial.print("O");            
          }
          if((char)e.bit.KEY == 'p')
          {
            Serial.print("P");            
          }
          /////////////////////////////////////////////////////// 
          ///////////////////////////////////////////////////////


          /////////////////Send UPERCASE second row////////////// 
          ///////////////////////////////////////////////////////
          if((char)e.bit.KEY == 'a')
          {
            Serial.print("A");            
          }
          if((char)e.bit.KEY == 's')
          {
            Serial.print("S");            
          }
          if((char)e.bit.KEY == 'd')
          {
            Serial.print("D");            
          }
          if((char)e.bit.KEY == 'f')
          {
            Serial.print("F");            
          }
          if((char)e.bit.KEY == 'g')
          {
            Serial.print("G");            
          }
          if((char)e.bit.KEY == 'h')
          {
            Serial.print("H");            
          }  
          if((char)e.bit.KEY == 'j')
          {
            Serial.print("J");            
          }   
          if((char)e.bit.KEY == 'k')
          {
            Serial.print("K");            
          }
          if((char)e.bit.KEY == 'l')
          {
            Serial.print("L");            
          }          
          /////////////////////////////////////////////////////// 
          ///////////////////////////////////////////////////////

          /////////////////Send UPERCASE third row/////////////// 
          ///////////////////////////////////////////////////////
          if((char)e.bit.KEY == 'z')
          {
            Serial.print("Z");            
          }
          if((char)e.bit.KEY == 'x')
          {
            Serial.print("X");            
          }
          if((char)e.bit.KEY == 'c')
          {
            Serial.print("C");            
          }
          if((char)e.bit.KEY == 'v')
          {
            Serial.print("V");            
          }
          if((char)e.bit.KEY == 'b')
          {
            Serial.print("B");            
          }
          if((char)e.bit.KEY == 'n')
          {
            Serial.print("N");            
          }  
          if((char)e.bit.KEY == 'm')
          {
            Serial.print("M");            
          }                      
          /////////////////////////////////////////////////////// 
          ///////////////////////////////////////////////////////

          SHIFT = false;                    //Finally, after we send the character we disable SHIFT.
        }   
        /////////////end of shift 
          
        else                                //If shift is not enabeled we send the normal character
        {
          if((char)e.bit.KEY == ',')        //"," will send a space
          {
            Serial.print(" ");           
          }
          else if((char)e.bit.KEY == '!')   //"!" will send a ^ for RETURN button
          {
            Serial.print("^");    //Return          
          }
          else if((char)e.bit.KEY == '-')   //"-" will send a - for OK button
          {
            Serial.print("}");     //OK         
          }
          else
          {
            Serial.print((char)e.bit.KEY);  //If not we just send the pressed character
          }
        }
        /////////////end of NO shift 
      }
    }   
  }
  delay(1); //Small belay between each loop
}








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