Enhancing Car Interiors with a Delayed Interior Light Circuit
This circuit falls under the realm of ‘car modding’, a trend akin to the widely popular case modding seen in the computer world, which has now significantly influenced the automotive sector. Car modding spans a wide spectrum of modifications, ranging from captivating light effects to the installation of complete in-car movie playback systems. While this particular circuit might not aspire to the grandeur of some automotive endeavors, it certainly presents an appealing and valuable addition. Specifically, it offers an enhanced interior light delay function. A feature already standard in many modern cars. Albeit predominantly present in the higher-end models equipped with automatic dimming capabilities. This circuit empowers car enthusiasts to upgrade second-hand and mid-range vehicles by providing an interior light delay feature that gracefully dims once the door is securely closed.
Generating Dimmed Interior Light: The Pulse-Width Modulation Technique
This circuit’s primary function is to achieve interior light dimming. A process realized through pulse-width modulation. Traditionally, generating a reliable triangular wave necessitates two opamps. Yet for this application, precision is not crucial. Consequently, a single opamp suffices to fulfill this requirement.
Operational Principles: IC1.A and IC1.B:
IC1.A functions as a relaxation oscillator, producing a square wave output. While the inverting input’s voltage exhibits a somewhat triangular form. This triangular signal can be utilized effectively as long as it isn’t subjected to excessive loads. IC1.B, characterized by its high impedance input, serves as a comparator. It compares the voltage from the triangular wave with the voltage across the door switch. When the door is open, closing the switch creates a short circuit to the car’s chassis, causing the output of IC1.B to go high.
Consequently, T1 conducts, illuminating the interior light. Once the door is shut, the light continues to shine at full intensity until the voltage across C2 aligns with the lower portion of the triangular wave, approximately 5 V. At this point, the comparator shifts its output in harmony with the triangular wave’s frequency, around 500 Hz. This gradually diminishing pulse width results in the interior light’s gradual dimming.
Fine-Tuning and Protection: R6, C2, R8, and C3:
The delay and dimming duration can be adjusted using R6 and C2, with smaller values leading to shorter durations. R1’s adjustment alters the dimming period independently by varying the triangle wave’s amplitude across C1. R7 governs C2’s discharge current, preventing premature capacitor wear. Notably, there’s no need for concern regarding the car battery’s lifespan.
The circuit’s minimal consumption, merely 350 μA when the lamp is off, paired with the utilization of TLC272 for the dual opamp (or about 1 mA with TL082), poses negligible discharge risk. For IC1, LM358, TL072, or TL062 are viable alternatives. With T1 operating in binary mode (fully on or off), minimal heat is generated. At 2 A, the transistor incurs a voltage drop of around 100 mV, translating to a mere 200 mW dissipation, eliminating the need for a heatsink. The entire circuit can maintain a compact profile, easily installed within the car, potentially concealed behind the roof fabric, ensuring seamless integration.