The process of decoding infrared signals by a TV receiver can be likened to a carefully choreographed dance in which the remote control is the conductor. When you press a button on the remote control, the chip inside the remote control generates a specific infrared signal according to a preset coding rule. This string of signals contains control commands and device address information to ensure that the signal can only be received by the target TV and not misread by other devices.
The remote control sends these signals through infrared emitting diodes, which are modulated at a frequency of 38kHz, a frequency rarely seen in natural light, so it can be well distinguished from ambient light and reduce interference. The signal consists of a series of pulses, the duration and interval of each pulse representing a different bit of data. For example, in the NEC protocol, logical “0” and logical “1” are distinguished by different durations of high levels.
When these infrared pulses reach the TV receiver, an infrared photodiode in the receiver converts the light signal into an electrical signal. These signals are then amplified, filtered and demodulated through a series of electronic components. The demodulation process is received through the infrared receiving tube, when the modulation signal is received, the output is low, otherwise the output is high. In this way, the receiver can convert the infrared signal into a digital signal, restoring the binary code sent by the remote control.
The microprocessor in the TV receiver decodes the incoming code, recognises which button has been pressed, and performs actions such as changing the channel or adjusting the volume. This process needs to be very fast and accurate to ensure an immediate response for remote operation.
In order to ensure the accuracy of the signal, the remote control will periodically emit the same coded pulse after the key is pressed, and the period is about 108ms. If the key is pressed for more than 36ms and is not released, the remote will send a repeat code, usually “FFFFFFFF” in the NEC protocol, indicating a long press of the key.
In general, the process of decoding the infrared signal by the TV receiver is a highly automated and precise process, which involves the coding of the remote control, the transmission of the signal, the demodulation of the receiver and the decoding of the microprocessor. This process ensures that we can easily control the TV from the remote control, and it all happens the moment we press the button.