Wiper Speed control. This project is about a simple automobile wiper speed control. The speed of the automobile wiper can be adjusted using a potentiometer using this circuit. The circuit operates from 12V DC and can be fitted to any automobile operating on 12V electrical system. With slight modification, the same circuit can be made to operate on 24V systems also.
The circuit is basically an astable multivibrator based on NE555 timer IC. IRF540 MOSEFET is used for driving the wiper motor. IRF540 is an n-channel MOSFET with excellent characteristics. Maximum drain source voltage is 100V, maximum drain current is 22A and the drain-source resistance during switch on is 0.055ohm.
The ON time of the astable multivibrator controls the sweep time of the wiper. It is governed by the equation Ton=0.69R1C1. The OFF time of the astable multivibretor controls the time between individual sweep cycles. It is governed by the equation Toff=0.69R2C1.Diode D1 by-passes resistor R2 during the charging of C1 and makes the ON time and OFF time independent of each other. Capacitor C2 is a noise by-pass capacitor. This capacitor prevents any noise from entering the chip through the control volatge(CV) pin.
When the output of NE555 (pin 3) is high MOSFET is switched ON and wiper motor is activated. When the output of the NE555 is low MOSFET is switched OFF and the wiper motor is held OFF. Resistor R3 limits the gate current of the MOSFET. Resitor R4 pulls down the gate of the MOSFET. Diode D2 is a freewheeling diode. It protects the switching device (MOSFET) from the voltage spikes produced when the motor is switched.
Setting up the circuit.