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Frequency Division Code remote control transmitter

Nov 16, 2017

Frequency Division Code remote control transmitter


In the infrared transmitter using a dedicated (color TV, VCD, DVD, etc.) infrared coding protocol for the encoder, the general electronic technicians or hobbyists, it is difficult to achieve, but the remote control launch of a small number of circuits , You can use the frequency division method of making encoders, but all the way to the remote control circuit, you can also do not have an encoder, direct launch 38kHz infrared signal, you can achieve the purpose of control.

Figure 1 is a one-way infrared remote control transmitter circuit, the circuit uses a high-speed CMOS IC2 4-2 input NAND gate 74HC00 integrated circuit, the composition of the low-frequency oscillator for the encoded signal (f1), with IC2555 circuit as a carrier oscillator, oscillation frequency: f0 (38kHz) f1: f0 modulation, so IC2 ③ pin waveform is intermittent carrier, the carrier is sent to the infrared light-emitting diode space. Circuit of the key points A, B, B 'waveform shown in Figure 2, where B' is not modulated waveforms.


In Figure 1, the 555 circuit is selected as a carrier oscillator, the purpose of which is to illustrate the modulation principle of the circuit, that is, using the familiar 555 to generate 38kHz square wave signal, and then use the 555 reset pin ④ modulation end, that is, when ④ feet is high, 555 is a conventional square wave oscillator; when the pin is low, 555 ③ feet at low level. The foot of the modulation signal is obtained by the IC1 NAND gate of the low-frequency oscillator.

In practice, the remote transmitter is powered by a 3V battery, which simply replaces the remaining 38kHz of the two NAND gates in the 555 circuit IC1, as shown in Figure 2.


Note: There is no reference to the CMOS4-2 input NAND gate CD4011 for the circuit in Figure 1, the encoder and carrier generator, because CD4011 oscillation for the generation of square wave signal, the application of analog signals. In order to ensure reliable circuit start-up, the operating voltage should be 4.5V above, while the 74HC00 CMOS IC minimum operating voltage of 2V, so the use of 3V power supply, fully reliable work.