Friday 1 July 2011

How does remote control in TV works?

In earliar days,remote were based on ultrasonics(sound frequency above the audible range of frequencies).The controlling circuitry included a hand held transmitter (that transmits ultrasound) and a TV-based receiver circuit.Electronic filters and stepper motors were used to allow/select certain frequencies and perform various functions depending on the key pressed.
But the  recent remote controls use infra-red(IR) rays and a special binary (0 and 1) coding menhanism.The code,intensity and wavelength of IR wave,help to select different functions.Depending on the key pressed,a signal is sent out by IR source,say,an injection laser diode(ILD).It generates a code in a parallel format.This is converted to a series format by a shift register.This signal is received by photo-sensitive devices such as an avalanche photo diode at the receiver.

Here another shift register is used to convert the code back to a parallel form.This operates a one-of-n decoder,which selects one function from a set of 'n' predefined functions and executes it.

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