Thomas Burrow

Traffic Light LED Conversion

I designed and implemented a new system for the old traffic light we have at my fraternity house. Caleb Jones made a fantastic SolidWorks model of the metal case and reflectors. This ensured that there would be room for the electronics and heatsinks.

I had spent some time working with high power LEDs, so I knew exactly what we needed. I chose to use a Vero 10 array for each color of the traffic light. These are about 20 watts each, producing around 2000 lumens for each of the three "bulbs". I knew thermal management and electrical regulation would be challenging. Each LED is mounted on a 1.25" round aluminum post, which conducts heat out to the steel case of the traffic light.

The system runs on 30V from an off the shelf switching power supply. Each LED has its own current regulator. As shown in the simplified schematic, an opamp compares the voltage across a shunt resistor to a reference divider. The opamp output drives a MOSFET gate, to sink 700mA through the LED (this worked very well). A linear voltage regulator provides 12V for the Arduino controller and opamp supply (that got pretty hot, because it was so inefficient). Areas of improvement should include neater routing and gate resistors, to prevent voltage spikes.

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