click from keyboard that stop arduino send data

Dear all I would like to press a keyboard to begin sending a data from Arduino such as S for start, also I would like to stop sending data from Arduino such as E for end and also I click on s again I ll start over

thank you

You need an application on the PC that monitors keystrokes, and sends them to the serial port that the Arduino is listening to.

On the Arduino end, it reads the serial port (Serial.available() and Serial.read()) to determine what to do, and Serial.print() and Serial.println() to send data to the serial port.

Have you got any code written that sends data from the Arduino that you would like to control ? How is the data being sent ? Serial, ethernet, wireless, IR or what ?