The Basics
Most remote controls work using infrared signals, invisible to the naked eye, which are beamed from the remote to the television set. The signals contain pulses which the TV receives as binary data: basically a set of 1s and 0s, which the TV interprets as different commands. Pushing the volume button relays one particular code that tells the TV to turn it up, while pushing the channel changer sends a completely different code telling the TV to switch stations.
LEDs and Circuit Boards
An LED (light-emitting diode) can be found on the end of the remote. It works in conjunction with an LED receiver on the television itself. When you push a button on the remote, it touches a contact point in the circuit board inside. The particular circuit then sends out the particular command through the LED emitter. The television picks it up and responds to it, and will keep responding as long as the button is touching the contact point. That's why the volume keeps going up or channels flip by rapidly when you hold down the button.
Universal Remotes
Universal remotes are designed to work with a wide variety of TVs as well as VCRs, DVD players and other devices. They usually require you to punch in a code corresponding to the device you want to control. The code tells the circuit board to send out the particular combination of IR pulses that match that brand of television. The list can be quite extensive, which is why universal remotes are a relatively recent invention. Older remotes simply didn't have sufficiently complex circuitry to handle every conceivable signal applicable to every conceivable TV.
Difficulties With Remotes
Most of the problems with remotes stem from realities about infrared light. Like any other light source, the LED emitters need power to run, and plugging them in to a power source defeats the whole purpose of a remote control. Almost every remote control relies on batteries to run effectively; when the batteries wear out, the remote stops working. Furthermore, IR light needs a direct light of sight to the receiver on the television. Like any other light, it can be blocked by objects such as furniture or people, a fact lost on many since the IR light is invisible to humans. Finally, the LED emitter has a limited range, much like a flashlight. Most remotes are only good for about 25 feet.
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