Petrol/diesel theft of parked vehicles is quite common. Presented here is an audio-visual anti-petrol theft alarm circuit that can help prevent this crime. The circuit consists of transmitter and receiver sections. The transmitter has to be mounted in the vehicle near the petrol tap, and the receiver in the common room of your house. When someone comes near the petrol tap, you get an audio-visual indication in your room.

Fig. 1: Transmitter section

The transmitter section (shown in Fig. 1) is built around an infrared LED (IR LED1), photodiode (PD1), comparator IC 741 (IC1), phase-locked loop IC 567 (IC2), 433MHz transmitter (TX1) and a few discrete components. Power supply to the circuit is given by the vehicle’s 12V battery through switch S1.

When someone comes near IR LED1, the IR signal reflected off the subject is detected by photo-diode PD1. A voltage difference appears at inverting pin 2 of IC1 and its pin 6 goes high. As a result, npn transistor T1 conducts and enables the PLL 567 to transmit a prefix frequency via transmitter TX1. LED1 glows when a signal is transmitted.

Fig. 2: Receiver section

The receiver section (shown in Fig. 2) is built around an infrared receiver module (RX1), PLL 567 (IC3), EFY-KnS 8051development board along with some discrete components. It operates off a 9V-12V battery. Alternatively, you can use a 12V adaptor. Switch S2 is used to power the circuit.

Transmitted frequency from the transmitter is received by the RF receiver module (RX1) and decoded by PLL567 (IC3). The output of IC3 is fed to input port pin P1.1 of EFY-KnS 8051 development board. The output port pin P2.2 is connected to transistor T2 to drive the buzzer and LED2. The EFY-KnS 8051 development board is used for speedy development and is available from EFY associates Kits’n’Spares (KnS).

The software is written in ‘C’ language on KEIL version 4.0 demo platform. Programming of the development board is simple and mentioned in the manual provided with the development board.

Assemble the transmitter and receiver circuits on two separate general-purpose PCBs. Connect the battery of the vehicle to the transmitter circuit. Fit IR LED1 and photo-diode PD1 of the transmitter such that if someone comes near the petrol tap, a signal can be transmitted through TX1. It would be better if you use a small 10mm wire as an antenna.

Mount switch S2 on the front side of the receiver unit along with LED2 and buzzer. Install the receiver PCB at your residence. When the receiver module receives a signal from the transmitter, LED2 will glow and at the same time buzzer PZ1 will sound.