How Everything Works
How Everything Works How Everything Works

Question 743

How does a TV or VCR remote control work? Is it infrared light or a laser? How does the TV or VCR know what to do with the light it receives from the remote? — FC, Lafayette, CA
The remote unit communicates with the TV or VCR via infrared light, which it produces with one or more light emitting diodes (LED). The most remarkable feature of this communication is that the TV or VCR is able to distinguish the tiny amount of light emitted by the LED from all the background light in the room. This selectivity is made possible by blinking the LED rapidly at one of two different frequencies. Since it's unlikely that any other source of light in the room will blink several hundred thousand times per second and at just the right frequency, the TV or VCR can tell that it's observing light from the remote. The remote sends information to the TV or VCR by switching back and forth between the two different frequencies. For example, it may use the higher frequency to send a "1" bit and the lower frequency to send a "0" bit. The remote sends a long string of these 1's and 0's, and the TV or VCR detects and analyzes this string of bits to determine (1) whether it's directed toward the TV or VCR (an address component in the information) and (2) what it should do as the result of this transmission (a data component in the information). Assuming that the string of bits was intended for the TV or VCR, its digital controller (a simple computer) takes whatever action the data component of the transmission requested.

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