SUN TRACKER

This is one of the pre-defined problem of IEEE Design Contest held at IIT Kharagpur in December 2004. I, Anil K.M, Rakhel Kumar Parida presented this  model and we got first in Sun Tracker Category and 3rd prize overall. Thanks to my senior  O.P.K  Reddy for making Mechanical part of it.Get pdf format of this one from Downloads section.

Sun Tracker is a mechanism which keep Solar Panels always perpendicular  to Sun. Everyday sun moves from East to West and a lateral shift of 23.5degree on both sides of normal.(see http://www.eaas.co.uk/news/seasons.html) So we need two axis tracking. Sun sets at west and our system shut downs automatically when a particular intensity of light is reached (i.e in night and in rain time). When it set at west and during morning it had to come back to east i.e in morning it had to shift 180 degree. Reddy had designed mechanical setup like that it will automatically comeback to east in morning, so there was no other electronic circuit for it. Our Sun Tracker worked perfectly with Sunlight and in darkroom in presence of sodium vapour lamp and it was a  success. Now our model is kept in IEEE section of IIT Kharagpur.

Components of Model

we used Aluminium sheets for making it. Motors of 1rpm(for  north,south movement), 3rpm for east,west movement. IC741,LM324,BC546,2N6107,KSD880 are other electronic components.

Motors: for east west movement which is required to hold the full mechanism+one motor for east west movement we used a good motor about Rs.400,250mA,2Kgcms,12V DC geared motor and for east west movement is simply DC motor with gears made by Reddy for his robots.

In this condition light intensity for LDR(4+3) will be greater than that for LDR(1+2). Therefore,Voltage across LDR(4+3),V4+3 > Voltage across LDR(1+2),V1+2

We can see in the circuit diagram that voltage across LDR 4 and 3 are added to form V4+3, similarly for V1+2. Now these signals are fed to a differential amplifier whose gain almost 100. This gain is the factor which will depend the efficiency of this system (maximum efficiency implies it will be strictly perpendicular to sun rays), ie with high efficiency even a small inclination can be tracked out. Therefore here,Y4+3 >Y1+2 IMPLIES Yd = A(Y4+3-Y1+2). So in this case Yd will be positive. This positive voltage will drive output of opx to positive saturation and output of opy to negativesaturation. ie Md = +Vcc to opx. Also Mu = -Vee to opy.

Thereby motor will rotate in such a way that Yd will decrease, and until Yd < Vmin, motor will rotate. Vmin is the voltage given to inputs of opamp(other than output from differential amplifier). This is done because, due to inertia the mechanism move some more extra distance, This makes the opx to -Vee and Vee to opy, this process continues just like a damping motion. This is avoided in such a way that a small voltage difference will be set between the sensors. That voltage will decide the preciseness of ckt. Less voltage more precise it will be. The same circuit is provided for the second direction.

LDR : It is light dependent resistor whose resistance depends on light intensity. The one whcih I used are having resistance in the range of 400 ohm to 450Kohm. Sensitivity of LDR is about 3msec. I tested it by connecting it to the input of an ADC and read ADC to parallel port. Then I continuously changed the light intensity and by applying a delay of 1ms in program. The best reading I noted it 3msec. Sensitivity is the time taken for output to change when input light intensity changes. Here sensitivity is of less importance because sun changes 1degree in 8minutes.

MOTOR DRIVING CIRCUIT

Here if the output of OPAMP is +Vee then transistor BC547 saturates which again saturates the complementary pair transistors and current flows through motor. At this time the other OPAMP will be at -15V so that the other BC548 will be cut off, thus other bridge will be open circuit so the current will be flowing through one bridge at a time only. Remeber one bridge will run motor in clockwise and other bridge will be in anticlockwise. The system stops due to friction.

When transistor is in saturation, Vce=.2V

so the current

Ic=Ie becomes Ic=(V-.2)/(1+1+5.6) mA

so the voltage drop at the emitter Ve=(Vcc-.2)*(1/(1+1+5.6)

Ve must be greater than .8V so that KSD880 become saturate.

voltage drop V2= (Vcc - .2)*((1+5.6)/(1+5.6+1)

so Vbe for 2N6107 becomes

Vbe= V -V2                                                                                                                                         This Vbe must be greater than .8V so that 2N6107 will saturate. In the case of 2N6107 it is a P N P transistor.So in the connection we can see that Emitter is connected to Vcc.Base is connected in such a way that Transistor E-B junction is forward biased. Thus both transistor both will conduct and the motor will rotate.

This circuit looks complex. So the motor driving circuitary can be made using L293 or L298 by replacing 741 by LM324 and the output of LM324 to the inputs of H bridge. Rember this circuit never stops motor. This mechanism stop due to friction

In this you can implement full circuit using 741(2), LDR(8),some resistors, 324(1),L293D(1).

This circuit is to shutdown the main power when sun sets or light intensity become low. When light intensity is low there is no need to keep this system ON

I used the following circuit at the last moment to get the proper output, because the gain 100 i explained previously is too high and the motor stop after too much time.

DATASHEETS

IMPORTANT NOTES

1.If you use IC741 as comparator with Vcc=5V and -Vee=0 then for HIGH=4.5V and LOW=1.52, so in both condition transistor will be saturated, so inorder to use IC741 as a comparator better apply -15,+15.

2. when LM324 is used with Vcc=5V then HIGH=3.6V and LOW=0. So this will be better, you won't be able to get HIGH=5V

3.In 741

when Vcc=5V,Vee=1.33V then HIGH=4.0 and LOW=0V. This is the reading which i got.

4. When I started writing this document I haven't got the original diagram,so in the starting the electronic ckts are not the real one which I used and the last one's numbered 1 to 4 are the actual one which i used,becaue the problem came was that at the last moment only I got this pdf file