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Objective:
The objective of this project is to understand the working of LDRs and Op-amps, which are a major part of the sun-seeker circuit. Also, to design and combine, the mechanical part and the circuit.
Sun-seeker:
A sun-seeker is a light/dark sensor circuit. It has a panel that faces the sun or any other light source, due to the light change on the LDRs (Light Dependent Resistors) in the network.
Equipment:
For Circuit:
Variable Resistors 2 LDRs 2 10kΩ Resistors 5 15kΩ Resistor 1 1kΩ Resistors 7 IC LM741 3 Transistor D313 4 DC Motor 1 Bread Board Vero Board Digital Multimeter Trainer Board Connecting Wires
For Mechanical Module:
Gears or Pulleys Board
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Circuit:
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The 3rd^ IC should act as an inverter with gain 1. Test both the LDRs by first exposing them to light and measuring their resistance, and then taking them in shadow. The first value should be low as compared to the second observation. Test the configuration of base, collector and emitter of the transistors, to see if the match the specified configuration. Carefully test all the resistors. The voltage source of the trainer board must also be tested with the help of DMM. Also test the connections in the Vero board, to see if they are not short.
Procedure:
First set both the circuits as shown in the circuit diagrams. Connect the respective ‘A’ and ‘Ā’ terminals of both circuits. By keeping the light intensity same on both LDRs, set the value of variable resistors until the motor stops moving.
Now check the direction of the circulation of motor, by changing the light intensity on one of the LDR, and then on the other. The motor should change its direction with the change in intensity on the pair of LDRs. If it moves in one direction then adjust the values of the variable resistors.
Working :
The 1st^ LM741 Op-Amp is taking the difference of the two inputs applied at the ends of the variable resistors.
The 2nd^ Op-Amp is a non inverting amplifier with a gain Av. It amplifies the input at its +ve terminal.
The gain Av is: Av = 1 + Rf/R 1
Therefore, for the circuit Av = 16
Since Rf = 1.5kΩ and R 1 = 100Ω
The 3rd^ Op-Amp inverts it’s input. It has a gain 1.
Same Light Intensity:
When the two LDRs have same light intensity on them, i.e. both are in dark or both are in light, the 1st^ Op-Amp gives (practical) output value close to zero, since both the inputs are same i.e. Vcc. This results the same output for 2nd and 3rd Op-Amps.
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Hence both the ‘A’ and ‘Ā’ terminals of the motor will give zero, and the transistors will remain OFF, since inputs at their base are all zero. Therefore the motor will not turn on when the both the LDRs have same light intensity on them.
Light Intensity on 1st^ LDR is greater than 2nd^ LDR:
When the light intensity on 1st^ LDR is greater than the 2nd^ LDR, its resistance will be less than the 2nd^ LDR. So most of the input at its end will be grounded because of LDR’s low resistance and a little amount of current will enter the – ve input terminal of the 1st^ OP- Amp.
On the other hand the other LDR’s high resistance will not allow the input current at its end to ground. So the input at +ve input terminal of the Op-Amp will be higher than the
- ve input terminal and hence the output of the 1st^ Op-Amp will be positive.
Therefore the value at ‘A’ will be positive and value at ‘Ā’ will be negative. So the transistors with ‘A’ terminal at their bases will turn ON and the current will flow in the indicated direction.
Light Intensity on 2nd^ LDR is greater than 1st^ LDR:
When the light intensity on 2nd^ LDR is greater than the 1st^ LDR, its resistance will be less than the1st LDR. So most of the input at its end will be grounded because of LDR’s low resistance and a little amount of current will enter the +ve input terminal of the 1st^ OP- Amp.
On the other hand the other LDR’s high resistance will not allow the input current at its end to ground. So the input at -ve input terminal of the Op-Amp will be higher than the +ve input terminal and hence the output of the 1st^ Op-Amp will be negative.
Therefore the value at ‘Ā’ will be positive and value at ‘A’ will be negative. So the transistors with ‘Ā’ terminal at their bases will turn ON and the current will flow in the indicated direction.
Result :
The motor is moving the panel in the direction of light, shaded on the LDR pair.
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Integrator Active filter Function generator
Transistor D313 :
The NPN transistor D313 is designed for use in general purpose amplifier and switching applications.
DC Motor :
Dc motors are normally used as prime movers in computers, numerically controlled machinery, or other applications where starts and stops are made quickly and accurately. DC motors have lightweight, low-inertia armatures that respond quickly to excitation- voltage changes.
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Veroboard :
Veroboard is a type of electronics prototyping board characterized by a 0.1 inch (2.54 mm) regular grid of holes, with wide strips running one way all the way along one side of the board. Breaks are inserted in the tracks, usually around a hole.
Breadboard :
A breadboard ( solderless breadboard , plugboard ) is a reusable solder less device used to build a (generally temporary) prototype of an electronic circuit and for experimenting with circuit designs.
