LED3 Solar Tracker Assembly

Introduction:
The Tracker PC board uses mostly surface mount parts. These components are difficult to assemble if you dont have the required skills and equipment. I am presenting these instructions for those who wish to attempt this task.

The assembly should be done in the specific order outlined to minimize the risk of damage to the circuits in case there are solder shorts or misplaced components.

Caution:
The components in this circuit are susceptible to damage through static discharges. Use normal static discharge prevention techniques such as a grounded workbench, soldering iron, and personal grounding wrist straps. Also the outer edge of the board is connected to the negative power terminal and should be the first point touched when handling the circuit.

Assembly Tools:

1. A low wattage temperature controlled soldering iron that can be set to 650F.

2. Solder paste. I use Multicore RMA mild activation rosin based solder paste in a 25 mG syringe (RM10). This paste contains 2% silver for excellent wetting action. Digikey part number SN62RM10.

3. Small diameter wire solder. I use Kester RMA mild activation rosin based 37/63 solder in .020 wire size. Digikey part number KE1201.

4. Toothpicks to apply the solder paste.

5. Metal tweezers for manipulating the tiny components.

6. Magnifiers or high magnification reading glasses. I use 3.5 or 4 diopter reading glasses.

7. Solvents to clean the solder flux. I use Asitone, available at building centers. This should be done in a well ventilated area. Asitone is Flamable so be careful.

8. A digital multi meter with sharp pointed probes for measuring resistance and voltage.

9. A current limited 12 volt power supply. Set to about .25 amps.

10. A bright light source for testing the tracker operation.

Assembly:
Whenever power is applied to the board it is wise to put a finger on the LM317LM to feel how warm it is getting. Any noticeable increase in temperature is an indication that the circuit should be immediately disconnected.

1. Apply all resisters, capacitors and transistors.

2. Add the connector to the backside of the board. The connector must be soldered on both sides of the board as my board manufacturer neglected to drill and plate these 4 holes. Do not solder the two center pins on the topside at this time. This will be soldered at a later time.

3. Measure the installed resistance of the components.

4. Check for shorts to ground at all component nodes.

5. Add the LM317LM making sure of the orientation of pin 1. Refer to the picture. Or an enlarges version at:
http://www.redrok.com/images/ledshex3.jpg

LED3
LED3

6. Apply 12 volts to the circuit through the connector.

7. Observe that the LM317LM is regulating to about 5 volts. And that there is about 1.4 volts on the four outer LED pad.

8. Add the 74HCT14.

9. Observe 5 volts on pin 14 and 0 volts on pin 7.

10.Observe pin 8 to see the oscillator output. This is mostly at 5 volts with short drops to 0 volts.

11. Add the 4 LEDs to the board. Leave the LEDs in the fanned out position as indicated by the position of the mounting pads. This gives the outer LEDs an additional 15 degrees angle.

12. Observe that the voltage on the input to pins 1 and 3 change voltage to between about 0 volts and 3volts when the LEDs are illuminated with a strong light source. Move the tracker about to see these voltages are changing.

13. Observe the voltage on the IRF7313 pads 1 and 3. These should be either 0 volts or 5 volts depending on orientation of the light source. There should never be 5 volts on the pins at the same time. (After final adjustment of the LED position its possible for them both to have 5 volts but not for now.)

14. Observe the voltage on the IRF7316 pads 1 and 3. These should be mostly at 12 volts with intermittent drops to about 4 volts depending on the orientation of the light source. For any orientation only on of the pins will be dropping to the lower voltage.

15. Add the IRF7313 and IRF7316 MOSFETs and solder the center two pins of the connector.

16. Make sure there are no shorts to ground or between the center connector pins.

17. Apply power and observe that the voltages on the center pins of the connector are pulsing dependent on the orientation of the light source. A test circuit with a pair of small red and green LEDs connected back to back and in series with a 470 ohm resister on the center pins of the connector will indicate which way the bridge is driving. The color indicates east or west movement dependent on the orientation of the light source.

18. Add the 1N5359 24 volt 5 watt zener diode between the positive terminal of the connector and the ground foil. The banded end is connected to the positive terminal.

19. Connect to a linear actuator and observe the operation of the actuator. The linear actuator must have limit switches, properly adjusted, with internal reversing diodes across the switches. This protects the driver from excessive current should the actuator run into the end of travel and stalls.

20. To temporarily disable the oscillator one can ground the foil on the backside of the board near the logo using your finger. This will activate the H-bridge continuously for testing.

LED3 Schematic
LED3 Schematic