Thanks for your suggestion...
In fact i have used an IR led transmitter and IR receiver to build my circuit. I have tried it in the bread board, use few switches connected to the data pin of HT12A (transmitter circuit) and use several LEDs at the data pin of HT12D (receiving circuit) and get a proper result...
However, when i use AT89c2051 to give signals to the data pin of HT12A instead of switches, it doesn;t work. What's the problem of my design??
Hope some one can give me suggestions...and a sample of source code is more preferable...Thanks....