In this tutorial, we are making a project of a simple car reverse horn circuit. the purpose of this circuit is to produce a musical horn when the car is in reverse gear. We have used two ICs in this circuit i.e. LM78L05 and UM66. LM78xx is a series of positive voltage regulators with three terminals, they come in a TO-220 package and the ‘xx’ here represents the voltage that the IC provides. The one that we are using is regulating a fixed voltage of 8 volts to the circuit therefore we chose LM78L05. The purpose of using this IC is that we are operating this circuit with a car battery that is 12V and the circuit needs only 8 volts so this IC will step down the voltage and provide a fixed voltage of 8 volts.
The other IC UM66 is a melody generator IC, it generates a melody as its output when receives an input signal.
Hardware Components
The following components are required to make Car Reverse Horn Circuit
| S.no | Component | Value | Qty |
|---|---|---|---|
| 1. | Battery | – | 1 |
| 2. | Reverse Switch | – | 1 |
| 3. | Voltage Regulator IC | LM7805 | 1 |
| 4. | IC | UM66 | 1 |
| 5. | Transistor | 2N3904 | 1 |
| 6. | Zener diode | 3V | 1 |
| 7. | Electrolytic Capacitor | 100µF, 10µF, 0.1µF | 1, 1, 1 |
| 8. | Resistor | 1K, 220Ω | 1 |
| 9. | Speaker | 8Ω | 1 |
LM7805 Pinout
For a detailed description of pinout, dimension features, and specifications download the datasheet of LM7805
UM66 Pinout
For a detailed description of pinout, dimension features, and specifications download the datasheet of UM66
Car Reverse Horn Circuit
Working Explanation
The circuit is simple, easy to build, and has very low power consumption. When the car will go in reverse gear the brake switch will be activated and provide power to the circuit and it activates. Now the 12V is stepped down to 8V through voltage regulator IC and these 8V are further stepped down to 5 to 3V with a Zener diode because UM66 is a low power IC and works on less than 5 volts. Now the UM66 will get the desired input signal to generate a melody. This melody will be amplified through a transistor and then sent to the 8 ohms speaker from where it can be heard. You can use any speaker of 8 ohms having an output power of 200mW to 1W.
Applications and Uses
This circuit can be used as a reverse horn for any vehicle that uses a 12V battery.
