Why does the infrared remote control use a 38KHz crystal oscillator?
The implementation of infrared remote control mainly consists of two parts: the infrared emitting end and the infrared receiving end. The emitting end is the infrared remote control we often use, while the receiving end is often electronic devices such as TVs and fans that need to be controlled by infrared.
Infrared emission part:
38KHz crystal oscillator
Encoding IC
Amplifying transistor
Emission tube
Battery
Infrared receiving part:
The infrared receiving part is mainly composed of a photodiode and an infrared receiving IC. The working principle is as follows: the photodiode (commonly known as a receiving tube) receives the light signal emitted by the infrared emission tube and converts it into an electrical signal (microampere-level current). This electrical signal is input to the receiving IC, and after amplification, gain, filtering, demodulation, and shaping, the original code given by the remote control is restored. The signal output by the receiving head is input to the code recognition circuit behind it.
The reason for selecting a 38KHz crystal oscillator:
The frequency of 38KHz output by the crystal oscillator can improve the anti-interference ability of infrared and avoid interference from infrared in the atmosphere. The modulation carrier frequency is generally between 30KHz and 60KHz, and most of the emitting ends use 38KHz. It should be noted that the duty cycle of 38KHz for most household appliance remote controls is 1/3, and there are also 1/2, but they are relatively less common. The original signal is a "0" or "1" data that we want to send, and the so-called 38KHz carrier is a square wave signal with a frequency of 38KHz. The signal sent out after modulation is the waveform that we finally transmit. We use the original signal to control the 38KHz carrier. When the signal is "0" data, the 38KHz carrier is completely and unreservedly sent out, and when the signal is "1" data, no carrier signal is sent.
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38KHZ Cylinder crystal datasheet