Although we're not finished with this part of the project yet we're going to release it unfinished for those who are following along.

We've decided to use the power window motors found in vehicles to move our solar panel array because the motors are 12 volts DC like the batteries the panels will be charging, the motors are strong, they have built in gear reduction and they're even reasonably cheap because they can be bough out of a car recycling yard. We like the power window drive motors from the older model vehicles because they're a little bit bigger and they have nice steel gears that'll stand up to some real work like pushing and pulling an array of solar panels.

Our projects uses six relays that we'll control with 3 I/O channels on the Basic Stamp 2 from Parallax Incorporated. We'll use 4 of the relays to switch the polarity of the electricity going to the motors and two of them as on/off switches. Each motor will need three relays for us to achieve multidirectional control. Since we'll only be moving in one direction at a time we can use the same polarity switching I/O channel for both motors.

Project Requirements

• All the Requirements of Sun Tracker for Your Solar Panels - Part 1
• 6 - 5 volt coil Compact Relays (We used the RAS-0510 from Steren Electronics)
• 2 - 12 volt Vehicle Power Window Motors
• 6 - NPN Transistors (Part #MPS2222A)
• 6 - Diodes (Part #1N4004)
• 6 - 220 ohm Resistors
• Miscellaneous Amounts of Wire

The Electronics
We're going to built 2 circuits that incorporate 3 relays, both of the circuits are exactly the same. One circuit will be used for up and down movement and the other circuit will be used for left to right movement.

A relay is an electrically activated switch. Our relays have a 5 volt coil so they will need 5 volts sent to the coil to make the relay switch to its' other position. We started by checking the relays' initial position by seeing if there was continuity between the switching poles and then marking each relay on the bottom with a felt pen to show the normal relay position.

Two of the relays will be used to change the polarity of the electricity going to the motor to get forward and reverse direction and the third relay in each circuit will be used as a basic switch. If needed we will send a signal to change the polarity, there will be a short pause and then the program will turn on the motors. The process will be reversed when we turn it off. The short pause is just a safety measure so that we are absolutely sure there is no electricity going to the relay until after the polarity is changed.

The Program for the Basic Stamp 2
The program that sends the signal and closes the switches for the motors to move the solar panel is very simple. We did add a short delay for protection when we switch the polarity in the parts of the program where we re-use the I/O channel. We used 1/2 second pulses on the motors but we may need to make corrections to this later when we've finished building the panel supporting hardware.

UP: 'Step Up (P4 is on switch)
DEBUG "UP", CR
HIGH 4
PAUSE 500
LOW 4
RETURN


DN: 'Step Down (P6 is polarity swtich & P4 is on switch)
DEBUG "DN", CR
HIGH 6
PAUSE 250
HIGH 4
PAUSE 500
LOW 4
PAUSE 250
LOW 6
RETURN


LE: 'Step Left (P5 is on switch)
DEBUG "LE", CR
HIGH 5
PAUSE 500
LOW 5
RETURN


RI: ' Step Right (P6 is polarity switch & P5 is on switch)
DEBUG "RI", CR
HIGH 6
PAUSE 250
HIGH 5
PAUSE 500
LOW 5
PAUSE 250
LOW 6
RETURN

You can try that out while we design the circuit boards and print them up.

Go to Part 1