Automatic Vehicle Headlight Dimmer with Ambient Light Sensing

High-beam glare from oncoming traffic is a genuine road-safety hazard — momentary blindness at closing speeds leaves no margin — yet most drivers dip their beams late or not at all, out of inattention or forgetfulness. Automatic high-beam systems exist in premium cars as sealed modules; the sensing principle, however, is simple enough to build and fully understand as a student prototype. This project implements it with an Arduino: a forward-facing LDR behind a simple lens tube measures oncoming light intensity, and when it exceeds a student-calibrated threshold the controller switches the headlamp relay from high to low beam. A short hold delay prevents flicker when the oncoming vehicle passes through the sensor's edge, and an ambient-light LDR arms the system only after dusk so daytime driving is unaffected. The build demonstrates threshold-based control, relay switching of a real load, and anti-flicker timing logic on hardware.

1. The ambient LDR continuously measures daylight; below the dusk threshold the system arms, otherwise it stays in manual pass-through.
2. When armed, the forward LDR is sampled every 100 ms; readings are smoothed with a short moving average to reject noise.
3. If the smoothed glare reading exceeds the calibrated threshold, the Arduino de-energizes the high-beam relay contact, dropping the lamp to low beam, and lights the LOW indicator.
4. When the reading falls back below the threshold minus a hysteresis margin, a hold timer (typically 2–3 seconds, design range) starts.
5. If the road stays clear through the hold period, the relay re-engages high beam; any new glare during the hold restarts the wait.
6. The hysteresis band plus the hold delay together prevent flicker at the threshold edge.
7. The manual override switch, when engaged, bypasses the automatic path entirely and the LCD flags MANUAL mode.

Tech stack:

• Arduino Uno (ATmega328P)
• 2× LDR light sensors with dividers (glare + ambient)
• 5 V relay module (high/low beam switching)
• 12 V automotive-style headlamp demo unit
• 16×2 character LCD + status LEDs
• Manual override switch
• Arduino IDE (C/C++ firmware)

• [Oncoming-glare sensing] A forward-facing LDR in a lens tube measures the intensity of oncoming headlights while rejecting most side and sky light.
• [Automatic high/low switching] The Arduino drives a relay that switches the headlamp between high and low beam filaments the moment glare crosses the calibrated threshold.
• [Anti-flicker hold delay] After the glare clears, the system waits a short hold period before restoring high beam, so a single passing vehicle does not cause rapid beam toggling.
• [Dusk-only arming] A second LDR measures ambient daylight and arms the dimmer only after dusk; daytime driving always stays on the driver's manual selection.
• [Manual override] A dashboard switch forces high or low beam regardless of the automatic logic, keeping the driver in ultimate control as road-safety practice requires.
• [Status indication] LEDs and a 16×2 LCD show the current beam state, sensor readings and whether the system is armed.
• [Student calibration] Both LDR thresholds are set by the student with a real headlamp at measured distances, logged on the calibration sheet — the trigger point is measured, not assumed.

• Working prototype: sensor head, controller, relay, demo headlamp, LCD
• Complete firmware (sampling, threshold logic, hysteresis, hold delay, override)
• LDR calibration procedure with distance-based log sheet
• Wiring diagram and 12 V automotive-style wiring notes
• Project report PDF (background, LDR sensing theory, control logic design, methodology)
• PPT presentation for final review
• Viva Q&A preparation document