This week, I decided to learn more Python language and create GUI interface. Therefore, I've been reading Python tutorials, taking an online class at Codecademy and practicing with small exercises.
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The first thing I did was to create simple GUI interface with Python, which can be eventually used to trigger blinking of LED from a PC. Below is the code and output.



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Next, I came to understand the major concept in using Python apps to control a board is communication between Python and the computer's serial port.

To blink an LED via Python, we can send a character to the board via serial so that the board can perform the routine written in c code. "Hi Python, send a character 'a' to serial port 6 (i.e. to a board that's connected to serial port 6). Below is code and I saved it as Blink.py.



Then, we define the onboard ledPin is digital pin 13. Setup Serial Communication to receive data from Python. Match the baud-rate with baud-rate in Python code. Since Arduino reads incoming data in ASCII. I found a=97 in ASCII. So the code says execute blinking when incoming serial equals to 97.

int led = 13;
void setup(){
  Serial.begin(9600);
}
void loop(){
  if (Serial.available() == '97'){
    digitalWrite(led, HIGH);
    delay(1000);
    digitalWrite(led, LOW);
    delay(1000);
  }
}

Compile and upload this code to an Arduino board.

Now, when you run Blink.py from command line, Arduino board will start blinking.
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Finally, I tried to connect dots to trigger LED blinking from GUI written in Python.



Then, modify Arduino code as follows:

int led = 13; // give a name to our LED
int ledStatus; // status of the LED. It's either HIGH or LOW (0 or 1)

void setup() {                
  pinMode(led, OUTPUT);  // initialize the digital pin as an output.
Serial.begin(9600);  // begin serial communication at 9600 baud
}

// main loop begins
void loop() {
  if(Serial.available() > 0) { // see if there is incoming data
    ledStatus = Serial.parseInt(); // parse the data and store the first integer, if available, into our variable. 
    digitalWrite(led, ledStatus); // Turn ON or Turn OFF the LED as per user input
  }
}