how can i send signal "a" to serial port of laptop

You can use the SerialPort class [^]to communictae with the serial port.

Hope this helps

ya u can
try this

include this name space 1st

using System.IO.Ports;

then create an serial object like this
SerialPort port = new SerialPort("COM1");
even u need to know the baurd rate of the system usually it will be 9600
to write into serial port use code
port.Write("A");

hope this will help u...

Use the SerialPort[^] Class:

SerialPort mySerialPort = new SerialPort("COM1", 9600, Parity.Odd, 8, StopBits.One);
mySerialPort.Write("a");