Automobile Fader Circuit Diagram: 700Hz & 5s Fade

Circuit diagram

Description

This circuit mirrors the "fading eyes" circuit previously presented and is commonly utilized for the gradual illumination and dimming of interior lighting systems in older automobiles.

The core of the circuit relies on the LM324, a low-power operational amplifier that consumes approximately 3mA of current, posing minimal drain to the vehicle's battery even when left connected for extended durations.

The uppermost two op-amps (pins 1,2,3 and 5,6,7) constitute a triangle wave oscillator operating at roughly 700Hz while the lower op-amp (pins 8,9,10) generates a linear, 5-second ramp, shifting upwards or downwards based on the position of the door switch. The two transistors and associated resistors are employed to regulate the ramp voltage, ensuring it remains within the slightly lower and upper limits of the triangle waveform. These two signals (700Hz triangle wave and 5-second ramp) are then applied to the inputs of the 4th op-amp (pins 12,13,14) which functions as a voltage comparator, producing a varying duty cycle square wave that controls the IRFZ44 MOSFET and the brightness of the lamp. The 5-second fade duration can be customized by adjusting the 75K resistor connected to the door switch; increasing the value will extend the time, while decreasing it will accelerate the process.

When the door switch is closed (car door open), the voltage on pin 8 progressively surpasses the negative peaks of the triangle wave, resulting in a short duty cycle output and a subdued light. As the ramp moves further positively, a larger percentage of the triangle wave will be beneath the ramp voltage, generating a wider pulse and a brighter light. This sequence continues until the ramp reaches 100% above the positive peaks of the triangle wave, and the output achieves its maximum value. Conversely, when the door switch is open, the reverse action occurs, and the lamps gradually fade out.

The IRFZ44 typically doesn't necessitate a heat sink if the total load is 50 watts or less; however, the MOSFET’s temperature should be monitored to guarantee it doesn't experience overheating. The on-state resistance is only 0.028 ohms, implying that 4 amps of current (48 watts) amounts to only approximately 100mW. For larger loads, a small heat sink can be added to maintain the MOSFET's cool operating temperature.

LM324 Operational Amplifier

The LM324 is a versatile, monolithic operational amplifier chip manufactured by Texas Instruments. It's a four-channel amplifier capable of operating in various configurations, including voltage follower, inverting amplifier, and summing amplifier. This particular chip is valued for its low power consumption, wide supply voltage range, and high gain, making it ideal for applications such as audio amplification, instrumentation, and control circuits. The chip has a fixed gain of 1000 for its unity-gain configuration and typically operates at a supply voltage of +/-15V. It provides excellent performance and stability, contributing significantly to the circuit's functionality and reliability. Its precision and ease of use make it a standard choice for many electronic designs.