Introduction: Sun Switch Simple Sun Tracking Electronic Device
Step 1: Its Simple ... Really Simple
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 instructable describes a sun switch built with a L6202 chip and a sensor built with 5mm GaP LEDs.
Step 2: The LEDs
LEDs (Light Emitting diodes) are cheap to purchase or can be found for free in scrap electronics. Many older keyboards have three or four LEDs that can be used for this project. They are usually the 3mm size and are semi transparent but they can be used for a sun switch sensor.
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.
Step 3: Build a Soldering Jig
Build a jig by cutting a piece of ABS pipe and drilling holes to hold the LEDs in place for soldering. If you use a drill bit that is the same diameter as the LEDs the LEDs will fit into the drilled holes very snugly. You can experiment by drilling test holes untill you find the correct size drill bit.
Build two sets of LEDs making sure they are arranged in the correct polarity. You can use any light gauge wire but I have found that stranded wire works best because it is flexible.
Step 4: Assembly of the Sensor Housing
Insert both sets of LEDs in the housing then insulate the leads with tubing or tape. Make sure you know the positive and negative leads of both sets of LEDs. Cut and cement a shadow plate between the east and west LED sets. Chamfer the edge of the plate and mount it parallel to the last row of the west LEDs.
Step 5: Electronic Circuit
Build the motor drive circuit. A large wattage ceramic resistor of a few ohms should be placed in series with the power supply to protect the circuit and motors from over heating during testing. This can be removed once the Sun Switch is completed.
Pin 2 - logic input to enable both outputs
Pin 4,5,6 - grounds
Pin 8 - output of second half bridge (motor drive)
Pin 9 - supply voltage to drive motors 12-24 volts
Pin 10 - output of first half bridge (motor drive)
Pin 11 - bootstrap to first half bridge output
Pin 12 - logic input (TTL) for first half bridge
Pin 13,14,15 - grounds
Pin 16 - logic input (TTL) for second half bridge
Pin 17 - bootstrap to second half bridge output
Pin 18 - internal reference voltage
C1 - 22mf 50volts electrolytic capacitor
C2 - .22mf SMD ceramic capacitor
C3,C4 - 10nf SMD ceramic capacitor
LEDs - 5mm 563nm Hi Green Water Clear
Drv - L6202 DMOS Full Bridge Driver
