Nikhil Mahadevan

2-Axis Light Tracker

A battery-powered dual-axis light tracker in bare-metal C on an ATmega328P with MOSFET H-bridges and a fixed-point Kalman filter.

ELEE 4230 Jun – Jul 2026
Source code Watch demo
Four-layer control board exported from the KiCad PCB. Click a part or a copper trace to see what it does.

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Highlights

  • Built a battery-powered dual-axis light tracker in bare-metal C on an ATmega328P, with motor control through MOSFET H-bridges
  • Combined an LDR array with Hall-effect and potentiometer feedback to keep tilt within safe limits and stop motor over-rotation
  • Implemented a fixed-point Kalman filter that reduced ADC noise from 3 LSBs to < 1 LSB without a Floating-Point Unit
  • Streamed raw and filtered ADC data, plus I/O data, to a PC over a register-level 115.2 kbps UART driver
  • Designed a 4-layer KiCad PCB with separate power, ground, and signal layers, and widened the power traces to reduce voltage drop

Overview

A closed-loop tracker that keeps a panel pointed at the brightest light source on two axes, with DC motors on both axes through MOSFET H-bridges. The firmware is bare-metal AVR C and handles everything on one microcontroller: sensing, filtering, motor control, safety limits, and telemetry.

Results

  • Kalman on the ADC path cut peak noise from ~3 LSBs to under 1 LSB on the LDR / pot / battery channels.
  • Hall end-stops latched cleanly in bring-up — analyzer captures show ~15 ms low windows used for limit timing (see gallery).
  • Four-layer KiCad board: ATmega328P, op-amp conditioning, MOSFET H-bridges; interactive 3D model above.

How it works

  • Sensing. Paired LDRs measure the light difference on each axis. Potentiometers report each axis’s position, and a resistor divider monitors the battery voltage.
  • Filtering. A fixed-point Kalman filter smooths the raw ADC readings from the LDRs, potentiometers, and battery monitor, cutting peak noise from 3 LSBs to under 1 LSB.
  • Control. When an LDR difference crosses its threshold, the firmware drives the base or panel motor toward the light through a MOSFET H-bridge.
  • Calibration and safety. At power-up the tracker sweeps each axis into its Hall-effect limit sensors to learn the potentiometer’s minimum and maximum ADC values. Latched software states then stop the motors before they over-rotate.
  • Telemetry. A register-level UART driver, clocked from a 9.216 MHz crystal so standard baud rates divide exactly, streams system status to Python logging scripts on a host computer.

Hardware

The control board is a four-layer KiCad design built around the ATmega328P, with MOSFET H-bridges for both motors, op-amp conditioning on the sensor inputs, an ISP header for programming, and test points on the key nets for bring-up. Explore the interactive board above, or the layout and schematic in the gallery.

See it follow a light source in the demo video.

Checkpoint reports

Weekly write-ups from ELEE 4230 (Sensors and Transducers), plus the final course report:

Checkpoint PDF
CP1 — Project idea, BOM, sensor selection Download
CP2 — Hall-effect sensor characterization Download
CP3 — LDR sensing and signal chain Download
CP4 — Capacitive touch input Download
CP5 — Enclosure, telemetry, demo Download
CP6 — Final report Download
Bench prototype — dual-axis frame, LDR shroud array, and DC-motor-driven panel on a rotating base.
System architecture from light and battery rail through sensing, the ATmega328P, H-bridges, and UART telemetry.
Analog path — LDR pairs, VBAT, and pot through unity-gain buffers and dividers into the 1.1 V ADC, with Hall limits and capacitive UART gating.
Main firmware loop — Kalman-filtered ADCs, ratiometric light thresholds, base/panel motor drive, and Hall/pot tilt limits.
Hall-effect sensors on the aluminum bracket and the magnet taped to the panel for tilt end-stops.
Logic-analyzer capture of Hall-effect boundary overshoot while the panel sweeps past a limit.
Hall I/O pulse with a measured ~15 ms low window used for limit timing.
KiCad layout, full schematic, and 3D board render — ATmega328P, op-amp conditioning, and MOSFET H-bridges.
Potentiometer signal conditioning — OP495 unity-gain buffer from POT V into POT ADC.
Homemade capacitive touch pad and 1 MΩ sense schematic used to gate UART logging.
Touch charge-time counter idle (~29) versus touched (rising into the hundreds).