Greenwatts

Sun Sensor

The Sun Switch sensor uses green GaP LED's to sense the position of the sun. When a GaP LED is pointed directly at the sun it will produce around 1.7 volts across the leads. By simply placing two or three of the LEDs in series you can provide enough potential to drive TTL logic inputs on a bridge driver.

The bridge driver circuit itself is simple and very easy to build. You can use any bridge driver chip that has TTL (digital input control) and is suitable for the size of DC motor to be driven. Parts to build a Sun Switch, motors, bridge drivers and LEDs, can be found in scrap electronics or computer hardware. This page describes a motor drive built with a L6202 chip and a sensor built with 5mm GaP LEDs.

Cut a 2" length of 1.5" ABS pipe which will be used as the sensor housing. Use the tool shown below to mark 3 lines spaced at 10mm around the circumference of the pipe. The tool allows you to easily mark lines perfectly perpendicular to the pipes axis by adjusting the pipe in the tool then rotating it with a drill while marking it. Also mark a cut line as shown which will be used to trim the pipe housing before attaching it to the drive unit. The tool is required because it is rather difficult to cut pipe at a perfect 90deg angle with a hand saw.

Layout the position of all the LED holes on the sensor housing as per the diagram below. There will be eight rows with three LEDs in each. Four rows of LEDs are connected in parallel and connect to either the east motor drive circuit or the west motor drive circuit. Center punch and drill the 24 LED holes in the sensor housing making sure that each hole is drilled perpendicular to the sensor housing axis and that each set of three holes are aligned parallel to the sensor housing axis. Each row is spaced 43 deg. apart and each LED is spaced .375" apart in each row. The east and west LEDs are separated by 23 deg. Use a proper size drill bit which will allow each lead to be firmly pressed into place. You can simply drill some test holes in a scrap piece of ABS to find the proper drill bit diameter.