Build Your Own: Automatic Windshield Wiper Circuit 12V

Description

Modern vehicles frequently incorporate a significant level of electronics, encompassing features like anti-lock braking systems, engine management with fuel injection modules, airbag deployment, and other auxiliary systems referred to as convenience features. Amongst these, a function is often overlooked due to its prevalence today: automatic activation of the windshield wipers for a brief duration following the release of the windshield washer fluid control. This practice is virtually indispensable, preventing the undesirable dripping of residual cleaning solution directly onto a recently cleansed windshield.

Regrettably, many budget-oriented vehicles or older models lack this automated function, a notably useful amenity. Consequently, since only a small number of components are needed, readily available to any competent electronics enthusiast, we will examine the circuit presented here. This project is remarkably straightforward and simply keeps the windshield wiper operating for a short time after the windshield spray system contact has been disengaged.

During the operation of the windshield washer pump, the 12 volts supplied by the battery are present at the terminals and therefore charge capacitor C1. Once the windshield spray system ceases, this capacitor can only discharge through R2, P1, R3, and the T1 emitter-base junction, due to the presence of diode D1. This maintains T1 in a conductive state for a specified duration, the precise length of which is dependent on the setting of P1. T1 subsequently saturates T2, which then performs the same for T3.

More about components

Integrated circuits, or ICs, are complex electronic circuits miniaturized onto a single semiconductor chip. These devices perform specific functions, such as amplification, switching, and logic operations. In this circuit, the transistors (T1, T2, and T3) function as switching elements, controlled by the DC voltage provided by the battery. Their small size and efficiency make them crucial components in modern electronics. These transistors, with a gain exceeding 25, are fundamental building blocks allowing for switching action and are a core element for this circuit’s functionality. They represent a key element for this circuit’s behavior and operation. These ICs are indispensable for the circuit to operate.

Circuit diagram:

The Re1 relay is therefore connected, ensuring the windshield wiper remains active because its contact is wired in parallel to the control switch. Upon C1 being sufficiently depleted, T1 is blocked, which then blocks T2 and T3, deactivating the relay Re1. The selection of components isn't supremely critical, though we denote specific references for T3; any low-power NPN transistor with a gain exceeding 25 will suffice. However, considering the power consumed by the windshield wiper motor, the relay Re1 must certainly be an ‘automotive’ relay.

These relays can be acquired at numerous automotive accessory stores (and sometimes at component retailers) at a very reasonable cost. These relays maintain contact under 12 volts and frequently possess only one contact, but they are generally capable of interrupting approximately 20 amps. The critical aspect of this project is accurately identifying the control wire for the windshield pump and the windshield wiper motor. Observing the signals at various points using a voltmeter should facilitate correct identification without significant difficulty.