Remote control receiver demodulation circuit
Figure 3 for the infrared receiver demodulation control circuit, IC2 in Figure 4 is LM567. LM567 is a phase-locked loop integrated circuit, 8-pin dual in-line plastic package, the operating voltage of +4.75? +9 V, operating frequency from DC to 500kHz, quiescent current of about 8mA. ⑧ feet for the output, static high level, is by the internal open collector transistor, allowing the maximum sink current of 100mA. In view of the more complicated internal circuit of LM567, only introduce the basic function of this circuit here.
LM567's ⑤, ⑥ pin external resistor (R3 + RP) and capacitor C4, determines the center frequency of the internal voltage-controlled oscillator: f01, f01 = 1 / 1.1RC, ①, ② foot connected capacitors C3, C4 to ground , Forming a filter network, where ② pin capacitance C2, determines the PLL capture bandwidth, the greater the capacitance, the narrower the loop bandwidth. ① feet connected capacitor C3 is more than 2 times the feet as well.
After the basic composition of LM567 has been clarified, analyze the working process of the circuit of Fig. 4 again. IC1 infrared receiver, which receives the infrared signal sent in Figure 1, the received modulated carrier frequency is still 38kHz, the received signal demodulated by IC1, OUT output at its output frequency f1 (see Figure 2) of the 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 transmits, LM567 to work, ⑧ feet from high to Low level, the low level makes the transistor 8550 turn on, output switching signal at point A to drive D trigger latch, and then it drives all kinds of switching circuits to work.
In this way, just press the microswitch K of FIG. 1 to transmit the infrared ray. The receiving circuit 4 can output the switching signal to turn on the control circuit, and then press the switch K to control the switching signal to be off. This completes the complete control function.