Larry's Blog

HANDHELD INFRARED REMOTES AND THE BINARY CODES

I have been using the PIC microcontroller to read the codes sent out from handheld remotes. I was even inspired to construct a maching that woulkd print out the various codes when I pressed one of the buttons on the remote. Here it is!

I got involved with this recently when Harold Parker of Parker Products in Reading, MA gave me a handheld remote and an IR receiver on a very small board to play with. I also found a good article in SERVO magazine for January 2005 on this subject. The IR signals are modulated on a 38khz carrier so that other stray signals can be filtered out. Other carrier frequencies are also used.
One favorite mode of sending the codes is PWM (pulse width modulation). In this method the 0's are send as a 400 usec pulse and the 1's are sent as a 1200 usec pulse. I programmed my PIC microcontroller to read these pulses and store the resulting data in memory. Note that this takes place in about 40 msecs. Once I have stored the data I can display it at my lesure with any means available. With my machine I chose to print out a red line on a strip of paper. Below is a sample.