This is something my son and I used as a sun tracker. The basic idea is that you hot glue four light sensors (we used photo-resistors) in each quadrant, and as the light moves off-center it casts shade on the opposite side. So maximizing the value of all the sensors will have it point to the brightest spot.

The design includes slots to drop in the sensors and allow the leads to go out the back. It also includes a hole down the center, which can be used to calibrate. (The light coming down the center hole will project a circle when pointed directly at the light.)

I've built it at various heights. A taller one is more sensitive to tiny changes in angle, but can cause a lot of "seeking", while a shorter one is more forgiving but less sensitive. Black filament works best to avoid reflections.

I've also included my Arduino sketch which may be a bit of a naive approach, but worked for our purposes. (This sketch and typical photoreceptors causes quite a bit of "seeking" right around the optimal value...)

You can test it by hot-gluing two servos together and the sensor to the top one to make a 2-axis tracker, as seen in the photo above.

Overview and Background

This device will point to the sun, or any bright light source. It does so by having 4 light sensors separated by walls hooked up to a microcontroller. As the sun moves, it will cast shade on a light sensor in the opposite direction. The microcontroller will detect which sensor has less light, and move the servos in that direction until the value of all the light sensors are maximized. The resulting angles are the position of the sun in the sky.

Lesson Plan and Activity

This is not a complicated concept, but due to the large number of wires (2x4+4 for each photoreceptor, and 3x2 for each servo) and breadboard parts, can get intricate. One can either build it ahead of time and use it as a measurement device (science), or build it in class and verify its functionality with a bright light (engineering). Recommended for teachers with existing knowledge of Arduino and breadboard work.

Materials Needed

1 Arduino 1 Breadboard 14 wires to the device (male-female recommended) 6 wires from the breadboard to the Arduino (male-male recommended) 4 photoresistors or photocapacitors 4 pull-down resistors (depends on the light sensors used)

Instructions

Best if printed with black filament, 1 shell, 100% infill. Wire photo detectors according to instructions for parts selected. Load Arduino with supplied sketch and calibrate for chosen detectors.