Problems Sending Signals to the Arduino-Uno via Keyboard

Question

I have an Arduino Uno and a usb 2.0 shield in which I connected a keyboard to. I have all the necessary libraries installed but what I am trying to figure out is how to light an led when I press a specific key.

I am new to codding Arduino boards and I have done a lot of reading but I cant figure out my issue I feel like if I get this figured out I will be a lot better off in my future projects.

#include <hidboot.h>
#include <usbhub.h>
#ifdef dobogusinclude
#include <spi4teensy3.h>
#endif
#include <SPI.h>

int SKEY = 8;

class KbdRptParser : public KeyboardReportParser
{
    void PrintKey(uint8_t mod, uint8_t key);

  protected:

    void OnKeyDown  (uint8_t mod, uint8_t key);
    void OnKeyUp    (uint8_t mod, uint8_t key);
    void OnKeyPressed            (uint8_t key);
};

void KbdRptParser::PrintKey(uint8_t m, uint8_t key)
{
  MODIFIERKEYS mod;
  *((uint8_t*)&mod) = m;
  Serial.print((mod.bmLeftCtrl   == 1) ? "C" : " ");
  Serial.print((mod.bmLeftShift  == 1) ? "S" : " ");
  Serial.print((mod.bmLeftAlt    == 1) ? "A" : " ");
  Serial.print((mod.bmLeftGUI    == 1) ? "G" : " ");

  Serial.print(" >");
  PrintHex<uint8_t>(key, 0x80);
  Serial.print("< ");

  Serial.print((mod.bmRightCtrl   == 1) ? "C" : " ");
  Serial.print((mod.bmRightShift  == 1) ? "S" : " ");
  Serial.print((mod.bmRightAlt    == 1) ? "A" : " ");
  Serial.println((mod.bmRightGUI  == 1) ? "G" : " ");
};

void KbdRptParser::OnKeyDown(uint8_t mod, uint8_t key)
{
  Serial.print("DN ");
  PrintKey(mod, key);
  uint8_t c = OemToAscii(mod, key);

}

void KbdRptParser::OnKeyUp(uint8_t mod, uint8_t key)
{
  Serial.print("UP ");
  PrintKey(mod, key);
}

void KbdRptParser::OnKeyPressed(uint8_t key)
{
  Serial.print("ASCII: ");
  Serial.println((char)key);
};

USB Usb;
HIDBoot<USB_HID_PROTOCOL_KEYBOARD>    HidKeyboard(&Usb);

KbdRptParser Prs;

void setup() { 
 
 Serial.begin(9600);
#if !defined(__MIPSEL__)
  while (!Serial); 
  Serial.println("Start");

  if (Usb.Init() == -1)
    Serial.println("OSC did not start.");

  delay( 1 );

  HidKeyboard.SetReportParser(0, &Prs);

}

void loop() {
 Usb.Task();
}

Anyways I know how to make if statements and how to activate pins on the Arduino but I cant figure it out in this keyboard library. For now I just made it print "TRUE" since there is not need to get complicated if I cant get the first step to work. Before I made that if statement the serial monitor would show the value assigned to the key and label it DN # and when I let up on the key it would say UP # but how can I translate that to sending a pulse to whatever pin when I push a key and stop sending a pulse when I let up on the key?

Also in my if statement that I made I know I need something before == sign but I tried multiple things and they did not work so I just left it blank and the reason I used the number 16 was because that was the value assigned to the S key in which I wanted to use to light an led. Anyways any help would be greatly appreciated!

Answer 1

Keyboards cannot be used quite like you wish - the keyboard will send a key (scan) code when a key is pressed and then repeat that code if the button continues to be pressed. There is a different code sent when the same key is released.

The scancode for key release is obtained from it by setting the high order bit (adding 0x80 = 128). Thus, Esc press produces scancode 01, Esc release scancode 81 (hex). For sequences things are similar: Keypad-/ gives e0 35 when pressed, e0 b5 when released. Most keyboards will repeat the make code (key down code) when the key repeats.

From: https://www.win.tue.nl/~aeb/linux/kbd/scancodes-1.html