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This circuit is similar to the fading eyes circuit above and is used to slowly brighten and fade interior lights of older cars.  The circuit is based around the LM324 low power opamp which draws around 3mA of current, so it won't bother the battery if left connected for extended periods. The top two opamps (pins 1,2,3 and 5,6,7) form a triangle wave oscillator running at about 700Hz while the lower opamp (pins 8,9,10) produces a linear, 5 second ramp, that moves up or down depending on the position of the door switch. Automobile Interior Lights Fader Circuit Diagram The two transistors and associated resistors serve to limit the ramp voltage to slightly more and less than the upper and lower limits of the triangle waveform. These two signals (700 hZ. triangle wave and 5 second ramp) are applied to the inputs of the 4th opamp (pins 12,13,14) that serves as a voltage comparator and generates a varying duty cycle square wave that controls the IRFZ44 MOSFET and lamp brightness. The 5 s...

The circuit employs two strings of series connected lamps. One string is complimentary to the other, this means that when one string fades the other string gains luminescence. Two power transistors 2N3053 are connected in complimentary mode as shown in circuit 1. The collector of the first transistor is connected to base of the second one through a 2.2K resistor. Different type of light source can be used by calculating the line current and bias voltages. Christmas tree bulb is a good option, as this bulb takes 200mA at 4V DC. Three numbers in series thus do not require any current limiting resistance when applied voltage is 12V DC , as shown in the circuit. 2N3053 can smartly handle up to 500mA of current and hence using the same transistor three strings of LEDs can be connected in parallel with a current limiting resistance of 220ohm, as shown in circuit 2. Four LEDs will be connected in a string, each LED chain will draw around 20mA of current. Hence, in practice, using th...