Introduction to the principle of single channel remote control switch

The remote control switch introduced in this article has the advantages of long remote control distance (greater than 30 meters), no direction restriction, wall penetration, stable operation, and compact size. As long as this circuit is added to the power supply circuit of home appliances, the home appliances can have remote control functions. The following introduces its circuit principle and production.

1. Circuit principle: 1. Remote control: The circuit is shown in Figure 1. The square wave signal generated by the multivibrator composed of T5, T6, etc. pulse modulates the 240MH--260MH radio frequency generated by the inductor three-point oscillator composed of T7, etc. The modulated radio frequency signal is radiated into space by the printed antenna of the circuit board. The battery used in the remote control is an A23 type 12V battery, which can usually be used for half a year and is easy to replace. 2. Receiving circuit: The circuit is shown in Figure 2. The ultra-high frequency receiving and demodulating circuit is composed of T1, L1, C0, etc. Adjusting C0 can calibrate the receiving circuit and the remote control to the best position. Its demodulated pulse signal is sent to the op amp A1A through R5 and C5 for comparison and amplification. The output signal is sent to the op amp A1B for peak comparison after passing through the C7, D2, D3 voltage doubling circuit. When the peak pulse at the inverting end of pin 6 exceeds the threshold voltage set at pin 5, pin 7 outputs a low-level signal that triggers the reversal of the bistable circuit composed of T2, T3, etc., controls T4 to turn on or off, and the relay to close or release. The integral delay function of R11 and C8 can effectively suppress and eliminate the interference of various short-time spike pulses on the circuit (such as lightning, fluorescent lamp on and off, etc.).

2. Production and debugging: 1. The remote control circuit is simple and generally works without debugging. What needs to be paid attention to is the selection of the transmitting tube T7 and the inductor. The amplification factor of T7 can be about 80. 2. The receiving circuit components are selected according to the parameters in the figure. The amplification factor of T1 is about 90, and the relay is a 12V micro relay. There are no special requirements for other components. 3. When debugging, press the remote control switch, connect the high-impedance headphones between the negative pole and the output pin of the op amp A1A, and then use a non-inductive screwdriver to turn C0 until the "beep" sound in the headphones is the loudest. After debugging, install the transmitter and receiver in suitable housings respectively. When using, connect the normally open contacts of the receiving circuit relay in series in the power supply circuit of the electrical appliance to be controlled, then press the remote control, the relay is energized, and the electrical appliance works. Press the remote control relay again to release the electrical appliance, and the electrical appliance is powered off.