The dominant remote-control technology in home-theater applications is infrared (IR). Infrared light is also known as plain-old "heat." The basic premise at work in an IR remote control is the use of light to carry signals between a remote control and the device it's directing. Infrared light is in the invisible portion of the electromagnetic spectrum.
An IR remote control (the transmitter) sends out pulses of infrared light that represent specific binary codes. These binary codes correspond to commands, such as Power On/Off and Volume Up. The IR receiver in the TV, stereo or other device decodes the pulses of light into the binary data (ones and zeroes) that the device's microprocessor can understand. The microprocessor then carries out the corresponding command.
To get a better idea of how the process works, let's take a look inside a typical remote control -- the universal remote that came with the author's digital cable box. The basic parts involved in sending an IR signal include:
- Integrated circuit
- Button contacts
- Light-emitting diode (LED)
To find out more about the parts on a remote-control circuit board, check out Inside a TV Remote Control.
On the component side, the infrared receiver sits on the front of the device where it can easily see the signal coming from the remote control.
You've probably noticed that some remotes only work when you're pointing them directly at the receiver on the controlled device, while others work when you're pointing them in the general vicinity of the receiver. This has to do with the strength of the transmitting LED. A remote with more than one LED and/or a particularly powerful LED produces a stronger, broader signal.
Now let's find out how these parts work together to allow pulses of light to change the channel on a cable box.