Tutorial: How to Use Arduino Uno as HID | Part 1: Arduino Keyboard Emulation

Arduino boards are pre-configured to function as serial device so to emulate keyboard, we will reconfigure it as Human Interface Device (HID) so our computer will see it as keyboard.

Video Demonstration:

Source Code:

uint8_t buf[8] = {
  0
};  // Keyboard Report Buffer: 8 bytes

#define PIN_W A0
#define PIN_A A1
#define PIN_S A2
#define PIN_D A3

//#define SERIAL_DEBUG  // for serial debug: remove //
                        // for actual HID: put //

bool currState_W = HIGH;
bool currState_A = HIGH;
bool currState_S = HIGH;
bool currState_D = HIGH;
          
bool prevState_W = HIGH; 
bool prevState_A = HIGH; 
bool prevState_S = HIGH; 
bool prevState_D = HIGH; 

unsigned long prevTime_W = 0;
unsigned long prevTime_A = 0;
unsigned long prevTime_S = 0;
unsigned long prevTime_D = 0;

unsigned long waitTime_W = 50;
unsigned long waitTime_A = 50;
unsigned long waitTime_S = 50;
unsigned long waitTime_D = 50;

void setup() 
{
  Serial.begin(9600);

  pinMode(PIN_W, INPUT_PULLUP);
  pinMode(PIN_A, INPUT_PULLUP);
  pinMode(PIN_S, INPUT_PULLUP);
  pinMode(PIN_D, INPUT_PULLUP);
  
  delay(200);
}

void loop() 
{
  checkButton();
}


void checkButton() {

  bool currRead_W = digitalRead(PIN_W);
  bool currRead_A = digitalRead(PIN_A);
  bool currRead_S = digitalRead(PIN_S);
  bool currRead_D = digitalRead(PIN_D);

  if (currRead_W != prevState_W) {
    prevTime_W = millis();
  }
  if (currRead_A != prevState_A) {
    prevTime_A = millis();
  }
  if (currRead_S != prevState_S) {
    prevTime_S = millis();
  }
  if (currRead_D != prevState_D) {
    prevTime_D = millis();
  }

  if ((millis() - prevTime_W) > waitTime_W) {
    if (currRead_W != currState_W) {
      currState_W = currRead_W;
      if (currState_W == LOW) {
        // Send the code
        buf[2] = 26;    // HID: W key
#ifdef SERIAL_DEBUG
        buf[2] = 'W';     // Serial: W key
#endif
        Serial.write(buf, 8); // Send keypress
      } else {
        // Release the keyboard
        releaseKey();
      }
    }
  }
  if ((millis() - prevTime_A) > waitTime_A) {
    if (currRead_A != currState_A) {
      currState_A = currRead_A;
      if (currState_A == LOW) {
        // Send the code
        buf[2] = 4;   // HID: A key
#ifdef SERIAL_DEBUG
        buf[2] = 'A';   // Serial: A key
#endif
        Serial.write(buf, 8); // Send keypress
      } else {
        // Release the keyboard
        releaseKey();
      }
    }
  }
  if ((millis() - prevTime_S) > waitTime_S) {
    if (currRead_S != currState_S) {
      currState_S = currRead_S;
      if (currState_S == LOW) {
        // Send the code
        buf[2] = 22;    // HID: S key
#ifdef SERIAL_DEBUG
        buf[2] = 'S';     // Serial: S key
#endif
        Serial.write(buf, 8); // Send keypress
      } else {
        // Release the keyboard
        releaseKey();
      }
    }
  }
  if ((millis() - prevTime_D) > waitTime_D) {
    if (currRead_D != currState_D) {
      currState_D = currRead_D;
      if (currState_D == LOW) {
        // Send the code
        buf[2] = 7;   // HID: D key
#ifdef SERIAL_DEBUG        
        buf[2] = 'D';   // Serial: D key
#endif
        Serial.write(buf, 8); // Send keypress
      } else {
        // Release the keyboard
        releaseKey();
      }
    }
  }

  prevState_W = currRead_W;
  prevState_A = currRead_A;
  prevState_S = currRead_S;
  prevState_D = currRead_D;

}

void releaseKey() 
{
  buf[0] = 0;
  buf[2] = 0;
  Serial.write(buf, 8); // Release key  
}

Arduino Uno R3 Original Firmware
Arduino Uno Keyboard HID Firmware

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