DIY Car Theft Detector with Alarm and Backup Energy

A easy, low-cost gadget can successfully alert householders or occupants if a parked car is moved or tampered with. This hardwired detector incorporates a predominant circuit with a buzzer alarm put in inside the home, whereas a sensor is mounted on the car being protected.

The sensor needs to be positioned on the car in a location shielded from warmth, rainwater, mud, and filth. Its leads have to be routed to an accessible level outdoors the car for simple connection to the wires coming from the primary circuit.

For constant safety, the sensor leads should stay linked to the primary circuit at any time when the car is parked. Any disconnection, reducing, or shorting of the wires triggers the alarm and prompts the LED indicator. The detector is powered by an exterior 12V DC adaptor, with a 9V dry cell offering backup throughout energy failures. Fig. 1 shows the writer’s prototype of the detector.

Circuit and dealing

Fig. 2 exhibits the circuit diagram of the car theft detector. The system is constructed round quad op-amp LM324 (IC1), quad 2-input NAND gate IC 7400 (IC2), and some different elements.

The quad op-amp IC LM324 (IC1) capabilities as a voltage comparator. The IC1A comparator detects increased voltage output from the sensor (within the dotted field) when the connecting wires (between TP1 and TP2) are short-circuited or linked whereas somebody makes an attempt to tamper with the car.

The IC1B comparator detects decrease voltage when the sensor wires are minimize or grow to be open-circuited. Potentiometers VR1 and VR2 present reference voltages for comparators IC1A and IC1B. Below regular circumstances, each comparators produce logic low outputs. Nonetheless, throughout voltage disturbances, the output of both comparator turns into logic excessive and provoke the alarm.

Elements Record

Semiconductors: IC1 (IC1A, IC1B, IC1E) – LM324 quad op-amp IC2 (IC2A-IC2E) – 74C00 quad NAND gate T1 – BC547 NPN transistor D1-D7 – 1N4007 rectifier diode LED1 – 5mm LED pink color Resistors (all 1/4-watt, ±5% carbon): R1 – 4.7kΩ R2, R7 – 3.3kΩ R3, R4, R6 – 10kΩ R5 – 5.6kΩ R8 – 2.2kΩ R9 – 1kΩ VR1, VR2 – 5kΩ potentiometer Capacitors: C1-C3 – 0.01μF ceramic disk C4 – 0.1μF ceramic disk Miscellaneous: S1 – Push-to-on swap CON1 – 2-pin connectors PZ1 – 12V piezo buzzer – Twin-core cable (requiredlength)

Building and testing

An actual-size, single-sided PCB format for the circuit is proven in Fig. 3, and its element format in Fig. 4. Alternatively, the circuit could be assembled as per Fig. 2 on a multipurpose board.

As soon as assembled, the mounted board needs to be enclosed in an appropriate enclosure with openings for the buzzer and LED indicator. A PVC electrical field, available at low price, is an efficient possibility. The sensor circuit could be soldered onto a strip of multipurpose board with sturdy results in join the primary circuit wires.

For testing, join the sensor (inside dotted traces within the circuit diagram) to the primary circuit PCB. Energy the circuit utilizing a 12V DC adaptor and a 9V backup battery.

Throughout calibration

• Alter potentiometer VR1 to three.85V and VR2 to 2.25V

• Join the safety wire loop between TP1 and TP2
• Open, quick and reverse; guarantee buzzer PZ1 and LED1 activate
• Press push button S1 momentarily to show off the buzzer and LED after connecting the safety loop between TP1 and TP2
• Repeat the exams utilizing a 9V battery, disconnecting the 12V DC adaptor

After passable testing, insulate and seal the sensor circuit in a small tube with epoxy compound, leaving solely the thick leads uncovered for exterior connection. The inner circuit of the sensor shouldn’t be seen to anybody.

Mount the sensor on the car and join it to the alarm circuit utilizing an appropriate size of weather-resistant twin-core cable. The connection close to the car could be achieved with crocodile clips, an auto wiring plug and socket, or some other connector sort, primarily based on consumer desire.

The way it protects your car from theft

The principle circuit, together with the assembled PCB, ought to stay inside the home. The car to be protected needs to be fastened with sensor and twin wire and linked between TP1 and TP2. If somebody makes an attempt to steal the car, the wire will break, triggering the buzzer to alert the consumer.

Warning

The 12V energy provide adaptor have to be of the mains-isolated sort, both step-down transformer and rectifier-based or SMPS sort. Non-isolated energy provides with capacitors or resistors for voltage discount mustn’t ever be used, as this might result in electrical shock or electrocution when connecting or disconnecting wires to the car sensor.

To make sure trouble-free operation, the connecting wires needs to be laid fastidiously in order that they don’t seem to be disturbed by close by folks, kids, or animals.

The gadget has been examined with a 20-metre-long, 1mm dia, single-core cable (two wires), as proven within the photograph. Nonetheless, such a thick cable is pointless. It’s endorsed to make use of a twin-core copper flat cable (23/0052, 1100V grade).

EFY notice. It will be higher to assemble D4, D5, R8, D6, and D7 on a zero PCB moderately than a PCB proven in Fig. 4. This meeting capabilities as a sensor. Repair it within the car and join the 2 ends of the sensor wires (from the car) to the terminals TP1 and TP2 of the primary circuit utilizing two-core lengthy wires.

Modification

If a louder hooter is required, a 12V sugar dice relay with a freewheeling diode could be linked in parallel to the prevailing buzzer. The hooter can then be linked by the relay’s usually open (NO) contact, powered by the 12V provide.

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P. Balasubramanian is a retired scientific officer from the Nuclear Energy Company of India Ltd (NPCIL). His areas of curiosity embody microcontrollers and energy electronics.