The TV remote control is mainly composed of a microprocessor chip, crystal oscillator, amplifying transistor, infrared light-emitting diode, and keyboard matrix that form the remote control signal. The working principle is as follows: the oscillator inside the microprocessor chip IC1 forms a high-frequency oscillator with the external oscillation crystal X through pins 2 and 3, generating a high-frequency oscillation signal (480kHz). After this signal is sent to the timing signal generator, a 40KHz sine signal and timing pulse signal are generated. The sine signal is sent to the encoder modulator as a carrier signal; The timed pulse signal is sent to the scanning signal generator, key input encoder, and instruction encoder as the time standard signal for these circuits.
The scanning signal generator inside IC1 generates five different time scanning pulse signals, which are output from pins 5-9 and sent to the keyboard matrix circuit. When a certain key is pressed, the control signal corresponding to the function key is input to the key encoder through pins 10-14, and outputs the digital signal of the corresponding function. Then, the instruction code signal is output by the encoder, modulated on the carrier signal by the modulator, forming a high-frequency pulse train containing functional information. The output from pin 17 is amplified by the transistor BG, which drives the infrared light-emitting diode D to emit a pulse modulation signal.