Design and production of power carrier remote control alarm circuit

Power carrier remote control is particularly suitable for home indoor use because it does not require additional wiring or occupying radio frequencies. Here we introduce a simple and easy-to-make power carrier wave remote control alarm, which may bring some convenience to your life.

working principle

Transmitting part (see Figure 1): The transmitting part consists of Q1 and Q2 connected into a composite tube to form a Hartley oscillator with a frequency of 135KHz. The power supply part with a voltage of 30 volts is composed of C2, D1, D2, D3, C5, etc. When the transmit button P1 is pressed, the 135KHz oscillation signal sensed by the secondary inductor of L1 is injected into the power line network through C1.

Receiving part (see Figure 2): The 135KHz sine wave from the transmitting part propagates through the power line to the receiving part and extracts the 135KHz signal through C1 and the frequency selection circuit composed of L1 and C3. This signal is amplified by Q1 and shaped into a square wave signal with an amplitude of 12V. D4 and D5 form a limiting circuit to ensure that the base peak voltage of Q1 is less than 1V to prevent various abnormal interference pulses in the power line network from damaging Q1. The function of D6 is to filter out the negative polarity part of the signal, and Q2 drives the alarm part to work. C7 is used here to keep the output part smooth and filter out the remaining parts of the signal. The 12V power supply part is composed of C2, D1, D2, D3, C5, etc.

Key points for production and debugging

1. During debugging, it is necessary to carefully adjust the magnetic core of L1 of the transmitting and receiving parts to ensure maximum output at both ends of C3 of the transmitting and receiving parts.

2. If possible, it is best to use an oscilloscope to observe the waveforms transmitted and received by each other during debugging at a distance.

3. If L1 uses the mid-circuit of a 455KHz medium wave radio, the output frequency should be about 135KHz when all the cores are adjusted to the lowest position.

4. If other L1 with similar resonant frequency is used, C3 of the transmitting and receiving parts must be adjusted at the same time, generally 1~3.3nF.

5. The output part can be used as buzzer or LED or both at the same time. If you only use LED, you can change R7 to 1K to increase its brightness. LEDs with a diameter of 10mm can be used.

6. When selecting components, please note that the withstand voltage of C1 and C2 of the transmitting and receiving parts must be greater than 400V. L1 can use the mid-circuit used in general medium-wave radios. If there are no special requirements for other components, please refer to Figure 1 and Figure 2 for selection.

7. Since the circuit part is directly connected to the 220-volt power supply, special attention must be paid during debugging to avoid direct contact with the circuit part to avoid electric shock. Before the device is put into use, the circuit part should be placed in a plastic box with reliable insulation and ensure safety and reliability before use.