Wirebook › Glossary › Infrared remote code
How does a TV remote send its buttons (infrared remote codes)?
In one sentence: The pattern of invisible flashes a TV remote sends for each button: a wake-up flash, then bits shown by long and short gaps, with a flipped copy as a check.
A little more
Most TV remotes send each button as a burst of infrared flashes. Every flash is itself a very fast flicker, usually around 38,000 times a second (38 kHz), and the TV's receiver chip only responds to light flickering at that speed, so steady sunlight and lamps are ignored.
In the widely used NEC code, a press starts with a 9 millisecond wake-up flash and a 4.5 millisecond pause, then sends 32 bits: an 8-bit address for the brand or device, the address with every bit flipped, an 8-bit command for the button, and the command flipped. Each bit is a 0.56 ms burst followed by a short gap (0) or a gap three times as long (1). The whole press takes about 68 ms, and holding a button sends a short repeat signal roughly every 108 ms. Other makers use different patterns and flicker speeds, which is why one brand's remote doesn't control another's TV.