Arduino and keyboard input

Hello everyone,

I'm trying to figure out a way to change a variable in my arduino code after the code has already been uploaded to the board using a keyboard. Any advice would be greatly appreciated. I'm guessing I will need to use some serial communication, but how would I collect keyboard data?


By "keyboard" do you mean a wired keypad... or do you mean from an attached PC?

Would be a good idea to post your code, then we can see how to help.

Slightly modified:

const byte ledPin = 13;      // the pin that the LED is attached to
byte incomingByte;      // a variable to read incoming serial data into

booelan ledState = false;

void setup() {
  // initialize serial communication:
  // initialize the LED pin as an output:
  pinMode(ledPin, OUTPUT);

void loop() {
  // see if there's incoming serial data:
  if (Serial.available() > 0) {
    // read the oldest byte in the serial buffer:
    incomingByte =;
    // if it's a capital H (ASCII 72), turn on the LED:
    if (incomingByte == 'H') {
      ledState = HIGH;
    // if it's an L (ASCII 76) turn off the LED:
    if (incomingByte == 'L') {
      ledState = LOW;
    digitalWrite(ledPin, ledState);

So, instead of entering 'H' or 'L', you want to be able enter, say "456" and assign that value to a variable in your program?

You're a good way there - you need to parse the number a digit at a time. There are plenty of examples around.

[EDIT] Sorry, that came out wrong. Lookup the function "atoi ()" - couple of things to watch out for; it works on strings, so you've got to build the string yourself a character at a time, and don't forget to terminate the string with a zero (which means your buffer has to be longer than the string you expect)

Okay I think i’ve figured out my own answer. I need to write a separate program, in python or C (or whatever) to send the serial data through the usb port. My arduino board would have a serial input check waiting for the incoming data…

That would be a good way of doing it if your Arduino is connected to yor Pc anyway.

I need to write a separate program,

You could just use the send box in the Arduino's monitor box to send stuff.