Friday, August 2, 2013

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Automatic solar tracking system

AUTOMATIC
SOLAR TRACKER starts following the SUN right from dawn, throughout the
day, till evening, and starts all over again from dawn next day. On
cloudy weathers, it remains still and catches the SUN again as it
slips out of clouds. It does all this automatically, employs cheap and
inexpensive components, and is very accurate.Let us see how it does
all this.

There are three Electronic Modules to be explained.
First one is the HORIZONTAL SENSOR MODULE. It employs the timer 555 in
the MONOSTABLE MODE. PIN 2(Trigger Pin of 555) is hooked up with a
VOLTAGE DIVIDER NETWORK(PLEASE see FIGURE 2). PIN 4(Reset) is hooked
up with ANOTHER VOLTAGE DIVIDER NETWORK.


Fig 1: Block diagram of the tracker following the sun all through Fig 1: Block diagram of the tracker following the sun all through
Fig 2: Horizontal sensor electronic circuit Fig 2: Horizontal sensor electronic circuit
The
LDR(SAY LDR A) which is always illuminated by light through FRESNEL
LENS ARRAY, has Low Resistance(in presence of light resistance of LDR
decreases and vice-versa). We know
V(OUT)=V(IN)*[R(bottom)]/[R(bottom)+R(top)], where R stands For
Resitance. So in SUNLIGHT, when LDR A’s resistance Decreases, VOLTAGE AT
PIN 4 Increases. TIMER is no more RESET. PIN 2 is now lower than 1/3
rd Vcc(as the horizontal LDR 1, say LDR B does not initially receive
light through its rectangular slit, so its resistance is high(Rtop=8 K
ohms), consequently V(OUT) is low). This triggers the timer which
gives a pulse to Decade Counter’s Clock(14) PIN and triggers it. The
Decade Counter CD 4017 gives a NORMAL STEP DRIVE pulse to the
Horizontal Unipolar Stepper Motor 1(coupled to the tracker unit) to
rotate the tracker position so as to receive sunlight(STEP ANGLE of 2
DEGREES). This goes on till the horizontal LDR 1 is fully in
SUNLIGHT(resistance low, so PIN 2’S VOLTAGE HIGH). Thus the tracker
has followed the SUN Horizontally.

Fig 3: Horizontal Sensor electronic circuit Fig 3: Horizontal Sensor electronic circuit
We
will come to the Vertical Sensor Module, but first let us see what
the DAWN LDR(SAY LDR C) does. At night the horizontal Module timer 555
remains Reset(as LDR A is in darkness so its resistance is high, thus
pin 4 voltage is low, and the TRACKER points at WEST(where SUN has
set). Next day when SUN rises again in the EAST, the DAWN LDR which is
located at the back of the TRACKER, points at EAST. So when it
receives sunlight its Resistance goes low, thus Voltage at pin 4 is
high and the timer triggers the Decade Counter which in turn switches
the Motor on, thus the TRACKER again moves towards the EAST. Then the
TRACKER functions as previously.

Now placed with the Horizontal
Sensor LDR 1 is another similar LDR 2 which receives the sunlight as
and when does LDR 1. SEE FIGURE 3. So now, as LDR B(THE 1st horizontal
one) receives sunlight, so does Horizontal LDR 2(SEE FIGURE 1, THESE 2
LDRs are placed together with same alignment properties and separated
by an optically insulated coating(from each other).Thus when Motor 1
comes to rest, and as the second horizontal LDR (SAY LDR D),is same
way coupled to the second timer’s(of Vertical Module) Reset pin as was
the ALWAYS ILLUMINATED LDR A, it brings the second timer out of its
Reset mode) by the previously discussed VOLTAGE RELATIONSHIP). EYE
SENSOR LDR(SAY LDR E) of the tracker receives sunlight by an
Anti-Reflection Coated, small Rectangular Slit, so reacts only when
SUN directly points at it. The second 555’s PIN 2 is same way
connected to this LDR as was the first 555’s to Horizontal LDR 1. So
now that it still not receives sunlight (resistance high, so Vout low)
and pin 4 is no more Reset, the second CD 4017 MAKES THE SECOND
STEPPER MOTOR 2 Rotate(Coupled so as to only rotate VERTICAL SENSING
BLOCK/EYE BLOCK ). This movement continues till the SUN directly
points at the EYE of our TRACKER. Then the TRACKER STOPS, pointing
very accurately at the SUN.FIG 2 and FIG 3 follows.

fig 4: Stepper motor control board fig 4: Stepper motor control board
In
figure 4 I have only shown the Horizontal Motor Control Circuit. The
Vertical One uses a similar Decade Counter, NPN Transistors, Diodes(to
encounter BACK EMF of Power Transistors due to Fast Switching). I
chose for a Step Angle of 2 Degrees for the Unipolar Steppers. They
are driven in a Normal 4 Step Sequence, first coil A is energised
simultaneously with coil B ,then coil C with coil D. Thus the Motors
rotate by 2 degrees each time. The Charging Interval(how long pin 3 of
555’s remains high) is almost in synchronism with the steps/second
speed of the motors(here 600 steps/sec.), to avoid FALSE TRIGGERING.

NOTE:

  1. For 555 in MONOSTABLE MODE, T=1.1*R*C.
  2. For
    the FRESNEL LENS ARRAY , the standard FL 40(Focal Length=0.4 inches)
    Or FL 65(Focal Length=0.65 inches) FRESNEL LENSES could be used (with
    the Grooves facing the LDRs).
  3. For the ANTI-REFLECTION COATING,
    MULTI-LAYER COATING could be used to minimize loss due to REFLECTION.
    By using alternating layers of a Low-Index material like SILICA and a
    Higher-Index material, it is possible to obtain Reflectivities as low
    as 0.1% at Single Wavelength

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