Description
Here is a 12 volt / 2 amp lamp dimmer that can be used to dim a
standard 25 watt automobile brake or backup bulb by controlling the duty
cycle of a astable 555 timer oscillator. When the wiper of the potentiometer
is at the uppermost position, the capacitor will charge quickly through both
1K resistors and the diode, producing a short positive interval and long
negative interval which dims the lamp to near darkness. When the
potentiometer wiper is at the lowermost position, the capacitor will charge
through both 1K resistors and the 50K potentiometer and discharge through
the lower 1K resistor, producing a long positive interval and short negative
interval which brightens the lamp to near full intensity. The duty cycle of
the 200 Hz square wave can be varied from approximately 5% to 95%.
The two circuits below illustrate connecting the lamp to either the positive
or negative side of the supply.
Circuit Diagram
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