Power line carrier remote alarm circuit diagram

The alarm introduced here does not require external transmission lines and relies on power lines to transmit alarm signals. Multiple alarm points can be set up to provide sound and light alarms for certain points. Has many uses.

working principle:

The alarm consists of two parts: transmitting and receiving display. The principle of the reflection circuit is shown in Figure 1. It is composed of two 555 time base circuits and two oscillation circuits with different frequencies. When both ends of CK are short-circuited (short-circuit alarm probe signal), the first (IC1) 555 constitutes a low-frequency oscillation circuit. The frequency F1 is mainly composed of C1, R2 determines that pin 3 outputs a low-frequency signal with frequency F1. When pin 3 of IC1 outputs high level, the high-frequency oscillation circuit composed of the second block (IC2) 555 works. Its oscillation frequency F2 is mainly determined by C3 and R4, and F2 It is much larger than F1, so the pulse modulation signal of F2 is output at pin 3 of IC2. The modulation signal generates high-frequency modulation pulses on the power line through a drive circuit composed of V1, T, C5, and C6. The high-frequency modulation pulse voltage is selected by the transmission distance.

The principle of the receiving and displaying circuit is shown in Figure 2. It consists of multiple frequency identification circuits. When an alarming high-frequency modulated pulse appears on the power line, the signal is sent to the first frequency phase-locked loop module (IC1) 567 through the voltage transformation of the T1 step-up transformer and the limiting of the current-limiting resistors R1 and D1~D4. 3 pin, and then the frequency identification circuit (R2, C4) composed of this frequency phase-locked loop determines the identification frequency value. Then the output pin 8 of IC1 can be connected to adjust the low frequency frequency of F1. One channel of the output frequency is sent to the drive circuit composed of V2 to drive the buzzer HD to produce an audible alarm; the other channel is sent to the second frequency identification circuit (IC2). In the same way, adjust the values ​​​​of R5 and C7 so that the second frequency demodulation circuit can access the frequency of F1, then (IC2) output pin 8 will change from high level, and L1 will light up, indicating that there is an alarm in the direction of the transmitting circuit. Affection.

Component selection and circuit adjustment:

The step-up transformer in Figures 1 and 2 uses a small audio transformer with a turns ratio of 1:20. The driver tube V1 in Figure 1 uses a BU506 power switch tube (output current is 500mA). C5 and C6 in Figure 1 and C1 and C2 in Figure 2 must use capacitors with a withstand voltage greater than 400V. CK in Figure 1 is used to connect the alarm probe; HD uses a finished buzzer with a voltage of 5V.

Since the entire machine circuit is connected to the power line, special attention should be paid to safety when adjusting the frequency of the transmitting circuit and the frequency of the receiving circuit. This alarm is only suitable for power lines within the range of the same transformer. At this time, the transmission distance can be up to 3Km.