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DIY Solar Tracker System .pdf

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DIY Solar Tracker System
The "Modular" design will allow you to
construct any size solar tracker, single or dual
axis, and adapt it to any type of device.
Photovoltaic PV solar panels, Solar
Concentrators, Solar Heaters Solar Cookers and
even mobile and marine trackers are possible
with our modular design. The new circuit
designed by Mike Mladejovsky, PhD uses an
inexpensive comparator integrated circuit and
Darlington pair transistor outputs to drive up to
a 1 amp DC motor. While this circuit can drive
large motors it is also possible to build minitrackers with input voltages as low as 3.6volts.
The sun sensor is simplified using only six
LEDs and the drive units are slew type designs
driven by planetary geared drill motors which provide lots of torque and are self locking.
As always you can build our trackers from recycled parts and cheap readily available
materials but we will also be making pre-made components available as well as
inexpensive kits. The circuit kit and fully assembled circuit boards will be available
starting early in June 2010.
The new drive units use a motor and gear set
from a battery powered screw driver or battery
powered drill providing lots of torque. A worm
gear is adapted to the chuck or drive shaft and
it turns a spur gear much like how a slew gear
works. For the first build I am using a Skill
Twist battery powered screwdriver and the
drive unit designed to handle a 2watt solar PV
panel. For the second build I will construct a
heavier drive unit using an 18 volt power drill
I do not have all the pictures available from the first build so if you have any questions
just post them on our comment section or send me an email and I will provide you with
more details. The first step is to dismantle your screwdriver, remove the batteries and cut
off the handle. Drill a small hole near the end of the motor and feed the motor wires into
the housing and solder them to the motor contacts as shown. Drill two pilot holes in the
end of the plastic screw driver plastic housing which will be used to attach the screw
driver to the gearbox housing in the next step.

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The next step is to make the worm gear and attach it to the drive. Cut a piece of threaded
rod 10cm in length and file down one end to fit tightly into the skill driver chuck and file
the other end to fit tightly into the center of a bearing. I used a recycled roller-skate wheel
bearing for this drive. Next cut one bottom (96mm x 96mm) and two side pieces (37mm
x 96mm) out of ABS flat stock to make the gear box housing. In one of the side pieces
layout and drill a center hole (17mm) and two mounting screw pilot holes to match the
screw driver chuck and the two pilot holes drilled in the previous step. Assemble the
gearbox housing with the side braces as shown in the picture below, with the worm gear
firmly inserted into the screwdriver chuck mount,
thread on a nut and press the bearing onto the
worm gear then secure the screw driver on to the
housing using two screws. The end of the worm
gear with the bearing should just touch the side
panel inside surface. Drill a hole in a piece of
ABS flat stock equal to the outside diameter of
the bearing, trim it square to fit the height of the
side panel and then cut it in half and cement it to
the inside of the side panel to hold the worm gear
bearing in place making sure the entire worm gear
assembly is aligned with the screwdriver. Place a
small amount of epoxy around the end of the screwdriver chuck then thread the bolt to
make contact and epoxy the bolt onto the worm gear as shown below.

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Cut a piece of threaded rod for the spur gear
approximately 10cm long. File down one end (8
to 10mm) to match the inside diameter of the spur
gear, press the spur gear onto the shaft and epoxy.
Note that this need to be a very tight fit to prevent
the spur gear from slipping on the shaft. We must
raise the spur gear to match the height of the
worm gear so we will make a small platform by
laminating several small squares of flat ABS
together. Once the height is matched add another
square piece with a hole drilled to match the
diameter of the bottom of the shaft. This will act as a shaft guide and bearing surface so
make sure it is loose enough to rotate freely but tight enough so there is no sideways
movement. Cement the platform into place making sure the spur gear meshes with the
worm gear while the spur gear shaft is perfectly vertical. Be careful not to make the spur
gear / worm gear contact to tight or it will bind.

Next step is to make a bearing surface on the spur gear shaft that will hold the shaft
where it penetrates the top of the drive housing. Measure about 6mm above the top
surface of the top of the housing by placing a flat piece of ABS across the top of the
housing sides and next to the shaft measure up 6mm then lock two nuts together with the
bottom of the two at the 6mm mark this will serve as a guide for filing the shaft. Use the
edge of a large flat file and file down a 6mm section just below the nuts to end up with
the shaft as in the bottom right picture. You can make the diameter equal to a 1/4 drill
which you will use later to make the split bearing.

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Take a piece of flat ABS stock to make the top of the drive housing and estimate where
the hole needs to be drilled for the spur gear shaft allowing for overhang on all four sides
of the drive housing which will be trimmed off later. Drill a hole slightly larger than the
3/8 shaft diameter that will fit over the spur gear shaft. Making sure the spur gear shaft is
perfectly vertical; tack cement to the top of the drive housing to ensure it is properly in
place. Now mark the under side of the housing top on all four sides, remove it and trim it.
Make sure to mark which side is up and after trimming it place it back in the same
position and securely cement it into place.

The split bearing holds the spur gear shaft in place while allowing it to rotate freely. Note
that you can place two of these on top of each other for added strength (you will need to
file down more length on the shaft to accommodate the second split bearing). To make
the slit bearing first drill a 1/4" hole in a flat piece of ABS plastic then trim around the
hole to make a 25mm square. Next simply cut the square in half through the center of the
hole. Making sure the shaft is perfectly vertical cement the split bearing into place as
shown. Let the cement dry and then check the rotation of the shaft by driving the motor in
both directions. The shaft should rotate perfectly on its axis and have no noticeable

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This step you will add reinforced mounting holes to the gear box on the end opposite of
the worm gear assembly. Follow the pictures below and cut out small rectangles to make
reinforced bolt hole mounts. You have to make sure there will be enough clearance to
insert a mounting bolt. For each side first cut a top and bottom piece cement then add a
vertical piece let the cement dry a little then add a inside vertical piece and a outside
vertical piece. Let the cement dry and then drill holes making sure you drill is as square
as possible to the gear housing. If you are off and can't insert a mounting bolt just enlarge
one of the holes slightly for more clearance.

The LED arrangement in the LM339 circuit
below uses two rows of three LEDs with each
LED connected in parallel, the two rows are
connected in parallel but reversed polarity. The
sensor array is made with three west LEDs and
three east LEDs. A 1meg resistor and a 10n
ceramic capacitor (103z) are also in parallel
with the sensor. The sensor LEDs provide input
voltage for two comparators on the LM339 chip
with the variable resistor R2 providing a "dead
zone" or sensitivity adjustment. Each
comparator output is fed into a transistor
Darlington pair which in turn drives the DC motor. The rail voltages are provided by two
batteries connected in series with the center tap providing the ground reference. We have
tested this circuit with 2 single cell lithium-ion batteries providing +/- 4.2 volts and two
12 volt lead batteries, the LM339 is rated for input voltages from +/- 2 volts to +/- 18

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volts. This circuit is the result of the design efforts of Mike Mladejovsky, PhD EE who
helped us solve issues with the solar tracker #3 circuits via the Electronics Tech Online
Forum which we highly recommend to anyone needing help understanding electronic
circuits. Many of the components in the following parts list can be substituted with
equivalent components such as using an AN6912 comparator instead of a LM339. We

use 5mm clear green super bright LEDs with a 40deg viewing angle but any clear lens
LED should work for the sensor. 1/4 or 1/2 watt resistors are adequate, fuses should be
placed on each rail and a DPDT switch can be used also.
• U1/U2 - LM339 quad comparator
• Q1 - TIP42C Power Transistor
• Q2 - TIP41C Power Transistor
• Q3 - 2N3906 Transistor
• Q4 - 2N3904 Transistor
• R1 - 1meg ohm
• R2 - 1k ohm trim pot
• R3 - 10k ohm
• R4 - 10k ohm
• R5 - 10k ohm
• R6 - 4.7k ohm
• R7 - 2.7k ohm
• C1 - 10n ceramic capacitor
• M - DC motor up to 1amp
• LEDs - 5mm 563nm Hi Green Water Clear

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Below is the printed circuit board
artwork for the LM339 circuit. The
board is 4.0cm x 4.0cm as
measured by the hash marks. The
traces are 1mm which should allow
you to etch the board using the
laser printer method. On the
artwork "B" indicates the battery
connections, "M" is the DC motor
connections and the LED
connections are at the top left. The
red dots indicate connections to the
positive +12volt rail, the green
dots are the -12volt rail
connections and the yellow dots
are the virtual ground.

Resize this image to approximately 8cm width and maintain the aspect ratio and you
should get the proper size printout depending on your printer. Check the width of the bar
at the bottom and right after printing it should be exactly 37mm.

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Below is an updated version of the PCB, we have reversed the orientation of the power
transistor Q1, changed the pad layout for the potentiometer and enlarged the pads for the
all the external connections, the power transistors and the potentiometer.

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Sun Sensor Unit
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
Build two LED sets consisting of 4 rows of 3 LEDs. You can build a simple tool by
cutting in half a short piece of 1.5" pipe and using it as a jig to solder the LEDs. Lay out
and drill an identical set of LED holes on the tool before you cut it. Place the LEDs
making sure of correct polarity then solder the leads using light strand wire.

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