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LIGHT / DARK SENSOR - ANIMAL FEEDER

CIRCUIT AND REVERSING A MOTORS DIRECTION OF ROTATION

V. Ryan © 2006 - 2019

 

PDF FILE - CLICK HERE FOR PRINTABLE VERSION OF EXERCISE SEEN BELOW

 

The sensor below is a light/dark sensor. This is part of an automatic animal feeder. As it becomes dark the sensor activates a relay that in turn turns on a motor, rotating a fly wheel. The fly wheel operates a mechanical system that releases food to a small animal, such as a hamster. Food is release during the night. This is electronics simulation software which allows the designer to draw a circuit in 3D and test it for faults.

   
 
The circuit below shows how a LDR can be used to reverse a motor. This may be useful in certain practical applications. For example, If an animal feeder has a lid that opens to reveal food and then closes, after a short time. The lid could be controlled by a motor, which in turn could be controlled by a LDR circuit.
 
 

1. A list of component names are seen below the diagram. Write each of the component names in the correct place on the diagram.

   
   
SNAP
LDR
CONNECTOR
  TRANSISTOR
RELAY
FLY WHEEL
  BATTERY
PCB
RESISTOR
  DIODE
MOTOR
             
 

 

 

2. Only one transistor is used in this circuit. The electronics simulation software 'Crocodile Technology 3D' has identified a possible fault - sometimes it is wise to include two transistors called a ‘darlington pair’ rather than the one transistor shown in the diagram above. Draw below a circuit diagram representing a darlington pair.

 

 

 

 

3. Why is it wise to use a darlington pair (two transistors) rather than a single transistor?
 
 
 
 
   
 
   

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