Sunday, June 5, 2011

12v 4amp Speed Control

A continuously working wiper in a automobile may show to be a nuisance, when it is not raining heavily. By using the circuit described here can vary sweeping rate of the wiper from one times a second to one times in0 seconds. The circuit comprises timer NE555 ICs, CD4017 decade counter, TIP32 driver transistor, a 2N3055 power transistor (or TIP3055) as well as a few other discrete parts. Timer IC1 is configured as a mono- stable multivibrator which produces a pulse when presses switch S1 momentarily. This pulse acts as a clock pulse for the decade counter (IC2) which advances by count on each successive clock pulse or the push of switch S1.0 presets (VR1 through VR10), set for different values by trial and error, are used at the0 outputs of IC2. But since output of IC2 is high at a time, preset (at selected output) effectively comes in series with timing resistors R4 and R5 connected in the circuit of timer IC3 which functions in astable mode. As presets VR1 through VR10 are set for different values, different time periods (or frequencies) for astable multivibrator IC3 can be selected. The output of IC3 is applied to pnp driver transistor T1 (TIP32) for driving the final power transistor T2 (2N3055) which in turn drives the wiper motor at the selected sweep speed. The power supply for the wiper motor as well as the circuit is tapped from the vehicle's battery itself. The period of monostable multivibrator IC1 is set for an very second period.

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