baud rate

hi
i am trying to write a program to send data to PC through air using LEDs and
photodiodes . i am using 4800 baud rate to comunicate .thus for approx 208microsec the led should toggle to send one bit. i have wriiten a program to toggle the led ,wait for 208 microsec and then toggle again.
BUT THATS NOT WORKING
data is displayed but not the one i try to send
Can anybody tell me how to calcute the delay time between two toggles for 4800 baud rate

If you connect the LED to the USART port of a PIC, and set-up the port correctly you should not have to worry about usec etc time. Don't know how well a photodiode will work at that speed though.

i am not using UART its already occupied .I have to built another using program.

aamirkhan said:

i am not using UART its already occupied .I have to built another using program.

Click to expand...

Hi,
If I understand correctly, you want to write the program for a 'software' UART.

Look at Nigels tutorials link, bottom of this post.

Use a wire connection first to debug the 232, and once you have it working use the LED, so that you can address one problem at a time. Never tried 232 in software so can't help you on that.

edit to add: If you use the LED/photo setup on your existing uart connection, does it work?

ericgibbs said:

Hi,
If I understand correctly, you want to write the program for a 'software' UART.

Look at Nigels tutorials link, bottom of this post.

Click to expand...

but i am using AT89S52 not PIC

aamirkhan said:

but i am using AT89S52 not PIC

Click to expand...

The same principles apply - basically that you usually require some kind of coding for IR or radio use, neither of which output the same width pulses you supply them.