Once upon a time, in the distant past, if you wanted to watch a different television program, you had to walk to the set and turn a dial. Today, however, you control your television, stereo, DVD player, and even the ceiling fan with the touch of a button on the remote.
Q: How do remote control devices work?
A: A remote control emits a signal from a diode that is similar to an LED. The wavelength emitted by a diode depends on the change in energy when an electron combines with a positively charged ion. Remote control devices use diodes made of silicon, in which the energy change is less than that of a light-emitting diode. Silicon diodes emit radiation in infrared wavelengths.
Because the radiation is in the infrared range, you don’t see it. But a receiver in the television set does. If you place something, or someone, between the controller and the receiver, it does not work because the signal is blocked.
There is always infrared light around, so the set also needs some way to recognize the signal from the remote. The signal is a series of flashes. A digital signal can be sent by switching back and forth between two frequencies. Part of the signal is set to identify the correct device (allowing a single remote to control several pieces of equipment) and part of the signal defines the desired action.
Now, when you pick up your remote control to change a channel, you know what it’s doing!
From The Complete Idiot’s Guide to the Science of Everything by Steve Miller