Download Solar Tracker CDS Circuit(NEW)

Solar Tracker CDS Circuit(NEW)
This solar tracking circuit features a further simplified design and very accurate tracking. It provides
fully automated solar tracking including morning reset to the east, automatic reset for cloudy periods
and brightness tracking to optimize solar PV performance on cloudy days. We have also simplified the
sun sensor array.
The circuit consist of clear green GaP LEDs for the sensor array which feed the positive and negative
inputs to a operational amplifier (op-amp) voltage difference circuit. The output of the op-amp biases a
PNP/NPN push/pull transistor curcuit which in turn drives the solar tracker DC motor either forward
(west) or backwards (east). This latest circuit no longer uses a CDS cell in the feedback portion of the
circuit. A zener diode on the PNP transistor dampens the east motor direction and prevents oscillation.
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4558DX General Purpose Op-Amp NTE x-ref
D2058/NTE377 NPN Transistor NTE x-ref
B601/NTE262 PNP Transistor NTE x-ref
Zener Diode - 5.6v (marking 5V6)
R1 - 10meg-ohm 1/2W resistor Resistor color codes
R2 - 5meg-ohm 1/2W resistor
R3 - 20k-ohm 1/4W resistor
R4 - 10k-ohm 1/4W resistor
8 LEDs - clear lens GaP green 5mm 40deg digikey.ca
The explanations in this section are aimed at anyone with limited knowledge of electronics,
electronic componments and circuit theory. I will make every attempt to clearly show how the
circuit works, how it is put together and what can go wrong. I will also show components and
how to identify and test them.
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You can referrence wikipedia for indepth information on any of the components above. I will
also explain how the batteries or DC supply is hooked up to the circuit as it uses a split power
supply of +12 volts and -12 volts which can be difficult to understand. The circuit is actually
quite simple by electronics standards and all the required components can be found in scrap
electronics. If you are building the circuit you should also read up on basic electronics
soldering how-to.
The sun sensor is made using clear lens 5mm GaP (green)light emitting diodes shown in the picture
below (left). The LEDs are mounted on a shaft that turns on the same axis as the solar panel (below
right). A LED is a semiconductor device and just like a solar cell it is photovoltaic, it will create
electricity if exposed to light. When a LED is pointed directly at the sun a potential (voltage) of aprox
1.7 volts will be created across the anode lead (positve) and the cathode lead (negative). We can use
this voltage as an input to a circuit and turn the LED into a solar sensor.
This is not the easiest way to make the LM339 circuit board but it is totally free and all the parts are
recycled. Start by finding a scrap board that has a section with little or no thru-hole components on it
(an area aprox 4cm x 4cm). Take a course file and simply file off the protruding leads on the trace side
of the board. The components will then just fall off fairly easily, remove all of the components and you
will be left with a blank
c
. 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 volts.
Many of the components in the following parts list can be substituted with equivalent components such
as using a 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.
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U1/U2 - LM339 quad comarator
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
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
lazer 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 aprox 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.