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In the remote control transmitting circuit, there are two kinds of circuits, namely the encoder and the 38kHz carrier signal generator. In application circuits that do not require multiple control, conventional integrated circuits can be used to form a few infrared remote control transmitting and receiving circuits. This circuit does not need to use a more complex dedicated codec, so it is easy to make.

Using dedicated (color TV, VCD, DVD, etc.) infrared coding communication protocol as an encoder at the infrared transmitting end is difficult for general electronic technicians or amateurs to implement, but it is difficult for remote control transmitting circuits with few channels. , You can use the frequency division method to make an encoder, and for a remote control circuit, you can also directly transmit 38kHz infrared signals without an encoder, and you can achieve the purpose of control.

One infrared remote control transmitter circuit. In this circuit, a piece of IC1 high-speed CMOS type 4-2 input "NAND" gate 74HC00 integrated circuit is used to form a low-frequency oscillator for encoding signal (f1), and IC2555 circuit for carrier oscillation The oscillation frequency is: f0 (38kHz) and f1 modulates: f0, so the waveform of pin ③ of IC2 is an intermittent carrier wave, which is sent to the space via infrared light-emitting diodes. The key points in the circuit are A, B, and B’s waveforms, where B’ is the unmodulated waveform.

The 555 circuit is selected as the carrier oscillator. The purpose is to illustrate the circuit's modulation working principle, that is, use the familiar 555 to generate a 38kHz square wave signal, and then use the reset terminal ④ of the 555 as the modulation terminal, that is, when the ④ pin is high power Normally, 555 is a conventional square wave oscillator; when pin ④ is low, pin 555 of 555 is low. ④ The modulation signal of the foot is obtained by the low frequency oscillator of the NAND gate of IC1.

In practical applications, the remote control transmitter is powered by a 3V battery, so only the 38kHz composed of the remaining two NAND gates of the 555 circuit IC1 need to be replaced.

Note: The NAND gate CD4011 input by CMOS4-2 is not used as the encoder and carrier generator in the circuit of Figure 1 here, because when the CD4011 oscillates to generate a square wave signal, it is an analog signal application. In order to ensure the reliable start-up of the circuit, its operating voltage needs to be above 4.5V, and the lowest operating voltage of the 74HC00 CMOS integrated circuit is 2V, so it can work reliably with a 3V power supply.