Here we are demonstrating a project of a simple contact-less reverse or backup alarm circuit. this circuit gets automatically activated when the car is in reverse gear and it will generate a loud melody that can be heard by anyone standing at the back of your vehicle and get alerted. This circuit can be used with any vehicle not just your car and it doesn’t require any installation therefore it is called contactless.
Hardware Components
The following components are required to make a Car Reverse Alarm Circuit
| S.no | Component | Value | Quantity |
|---|---|---|---|
| 1 | Lithium coin cell battery | 3V | 2 |
| 2 | IC | UM66 | 1 |
| 3 | LDR | 1 | |
| 4 | Transistor | 2N3904, 2N4401 | 1, 1 |
| 5 | Electrolyte Capacitor | 0.1µF | 1 |
| 6 | Zener diode | 3V | 1 |
| 7 | Resistor | 1KΩ | 1 |
| 8 | Variable Resistor | 50KΩ | 1 |
| 9 | Speaker | 8Ω | 1 |
UM66 IC Pinout
For a detailed description of pinout, dimension features, and specifications download the datasheet of UM66
2N4401 Pinout
For a detailed description of pinout, dimension features, and specifications download the datasheet of 2N4401
Car Reverse Alarm Circuit
Working Explanation
To make this circuit work connect it to the reverse light of your vehicle. A photoresistor is used to sense the vehicle light and the circuit will activate. The circuit can be operated at 6 volts DC with a lithium coin cell as supply. When the circuit activates it will activate the UM66 IC that will generate the melody. The output of this IC is amplified by a 2N4401 transistor you can use a BD139 transistor instead if you want to increase its loudness of it. An 8 ohms speaker is used at the output of this circuit.
For best performance fit the circuit in a small box and make a small hole for the photoresistor and leave it inside the box in front of the small hole so it receives just the vehicle light or else it will produce melody on other lights. Use another box for a speaker if the speaker is a big one like 0.5 or 1 watt and hide it somewhere in the back of the car. The sensitivity of the circuit is adjusted by the 50K variable resistor.
