Single-channel remote control switch - power supply circuit - circuit diagram - Huaqiang Electronic Network

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This article discusses a remote control switch that boasts a long-distance operation (greater than 30 meters), no directional limitations, and the ability to penetrate walls. It operates stably and is compact in size. By integrating such a circuit into the power supply circuit of a household appliance, the device can gain remote control functionality. Below is a detailed description of its circuit principle and production process.

Firstly, let’s explore the circuit principle: 1. Remote Control: As shown in Figure 1, a multivibrator made up of T5, T6, etc., generates a square wave signal, which serves as the input for the 240MHz–260MHz RF signal produced by the inductor three-point oscillator formed by T7. This RF signal is pulse-modulated and radiated via the printed antenna on the board into the surrounding space. The battery used in the remote control is an A23-type 12V battery, which offers a usage time of approximately six months and is easy to replace. 2. Receiving Circuit: As depicted in Figure 2, the UHF receiving and demodulating circuit consists of T1, L1, C0, etc. Adjusting C0 allows for optimal alignment between the receiving circuit and the remote controller. The demodulated pulse signal is sent to the operational amplifier A1A via R5 and C5 for comparison and amplification. The output signal is then sent to the operational amplifier A1B after passing through the C7, D2, and D3 voltage doubler circuits for peak comparison. When the 6-pin inverting terminal detects a peak pulse exceeding the threshold voltage set by the 5-pin, the 7-pin outputs a low-level signal, triggering the bistable circuit composed of T2, T3, etc., causing T4 to conduct or cut off, thereby pulling or releasing the relay. The integral delay function provided by R11 and C8 effectively suppresses and eliminates various short-duration sharp pulse interferences (e.g., lightning, fluorescent lights).

Secondly, the production and debugging process: 1. The remote control circuit is relatively simple and usually functions without requiring additional tuning, but it is important to carefully select the transmission tube T7 and inductance. The amplification factor of T7 should be around 80. 2. Components for the receiving circuit are chosen based on the parameters in the diagram. The amplification factor of T1 is approximately 90, and the relay is a micro relay rated at 12V. Other components do not have any special requirements. 3. During debugging, press the remote control switch and connect the negative pole to the A1A output pin of the op-amp using a high-impedance earphone. Then adjust C0 with a non-inductive screwdriver until the "beep" sound in the earphone reaches its maximum volume. Once the commissioning is complete, the transmitter and receiver are installed in appropriate casings. In use, it will receive the normally open contacts of the circuit relay, connecting it to the power supply circuit of the appliance being controlled. Pressing the remote control causes the relay to engage, activating the appliance. Pressing the remote control again disconnects the relay, turning off the appliance.