Remote Control Circuit design
Remote control circuit design editing
In the remote control transmitter circuit, there are two circuits, namely the encoder and 38kHz carrier signal generator. In application circuits that do not require multiple control, conventional infrared circuits can be used to form a few infrared remote control transmit and receive circuits, which do not require the use of more complex dedicated codecs, making it easy.
Frequency-division coded remote control transmitter
In the infrared transmitter using a dedicated (color TV, VCD, DVD, etc.) infrared coding protocol for the encoder, the general electronic technical staff or amateurs, it is difficult to achieve, but the few few remote control transmission circuit , You can use the frequency division method to produce the encoder, and all the way to the remote control circuit, you can not use the encoder, direct launch 38kHz infrared signal, you can achieve the purpose of control.
Is a way of infrared remote control transmitter circuit, in this circuit, the use of a IC1 high-speed CMOS 4-2 input "NAND gate" 74HC00 integrated circuit, composed of low-frequency oscillator for the encoded signal (f1), with IC2555 circuit As the carrier oscillator, the oscillation frequency is: f0 (38kHz) f1 on: f0 modulation, so IC2 ③ feet of the waveform is intermittent carrier, the carrier sent to the infrared light-emitting diode. The key A, B, B 'waveforms in the circuit are shown in Fig. 2, where B' is an unmodulated waveform.
In Figure 1, the choice of 555 circuit as a carrier oscillator, the purpose is to explain the principle of circuit modulation, that is, we use the familiar 555 38kHz square wave signal, and then use the 555 reset terminal ④ feet for modulation, ④ foot is high, 555 is a conventional square wave oscillator; when the ④ pin is low, 555 ③ feet in the low level. ④ foot modulation signal is IC1 NAND gate low-frequency oscillator and get.
In practical applications, the remote control transmitter is 3V battery-powered, this only need to 555 circuit IC1 remaining two non-gate composed of 38kHz instead.
Note: This is not quoted CMOS 4-2 input "NAND gate" CD4011 Figure 1 circuit encoder and carrier generator, because the CD4011 for oscillation to generate square wave signal, is an analog signal applications. In order to ensure reliable starting circuit, the operating voltage of 4.5V or more, and 74HC00 CMOS integrated circuit minimum operating voltage of 2V, so the use of 3V power supply, can be reliable work.
Remote receiving and receiving demodulation circuit
Figure 3 for the infrared receiver demodulation control circuit, Figure 4 IC2 is LM567. LM567 is a phase-locked loop integrated circuit, 8-pin dual-row plastic package, the working voltage of +4.75? +9 V, the operating frequency from DC to 500kHz, quiescent current of about 8mA. ⑧ feet for the output, when the static is high, is composed of internal open collector transistor, allowing the maximum sink current is 100mA. In view of the LM567 internal circuit is more complex, here only describes the basic functions of the circuit.
LM567 ⑤, ⑥ feet external resistance (R3 + RP) and capacitor C4, determines the internal voltage-controlled oscillator center frequency: f01, f01 = 1 / 1.1RC, ①, ② feet connected capacitor C3, C4 to ground , The formation of filter network, which ② capacitance C2, determine the phase-locked loop capture bandwidth, the greater the capacitance, the narrower the loop bandwidth. ① feet of the capacitor C3 for the ② feet more than 2 times as well.
After the basic composition of the LM567 is clarified, the working process of the circuit of Fig. 4 is analyzed again. IC1 is the infrared receiver, it receives the infrared signal sent in Figure 1, the received modulation carrier frequency is still 38kHz, the received signal by IC1 demodulation, in its output OUT output frequency f1 (see Figure 2) square wave signal , As long as the LM567 center frequency: f01 transferred to (with RP) and the transmitter f1 (see Figure 2) the same, that f01 = f1, then when the transmitter launch, LM567 work, ⑧ feet from high to Low level, the low level of the transistor 8550 conduction, the output signal in the A point to drive D trigger latch, and then it is driven by a variety of switching circuit work.
In this way, as long as the circuit shown in Figure 1, the micro-switch K, that is, the emission of infrared, the receiving circuit can be output switch signal 4 open control circuit, and then press the switch K, control switch signal is closed, which completed a complete control function.