University of Arkansas - AgriScience Project

AGRISCIENCE EXERCISE

PHYSICAL SCIENCES IN AGRICULTURE

Key Concept: Electricity and Electronic Systems

Sub-Concept: Electronics

Agricultural Application: Basic electronics principles are applied i common agricultural equipment.

Exercise: Constructing a Light Controlled Switching Circuit

Applied Principle(s): Basic principles of electricity

Goals:

  1. Interpret an electronics circuit schematic.
  2. Assemble a light controlled switching circuit that will function as specified.
  3. Explain the operation of the circuit.
  4. Describe possible agricultural applications.


Materials:

Procedures for Conducting the Activity:

1. Divide the class into small groups of no more than 3 students each.

2. Provide each student with an instruction/data sheet, and allow the class time to read the entire activity and attached information sheet before proceeding.

3. Provide each group with the necessary materials.

4. Allow the students to proceed through the activity, providing assistance as necessary.

5. When all groups have finished, discuss the activity questions and results as a class. Discuss the practical applications of the knowledge gained through the activity.



AGRISCIENCE EXERCISE

- Constructing a Light Controlled Switching Circuit -

Student Data/Instruction Sheet

1. Read the attached information sheet before proceeding through this exercise, to gain a better understanding of the relationship between the principles.

2. Secure the following equipment and supplies:



3. Assemble the light controlled switching circuit as shown in the schematic below. (Note: Identify the correct transistor and relay connections by referring to the diagram on the respective device package. Do not discard these packages.)























4. Test your circuit as indicated;

A. Place your completed circuit on a table under a bright artificial light.

B. Turn the potentiometer shaft and observe the lamp fixture. If the circuit is properly constructed, you should be able to turn the lamp fixture "on" and "off" by adjusting the potentiometer.

C. Adjust the potentiometer to the point where the lamp fixture just goes "off."

D. Cover the photocell with your hand and see if the lamp fixture comes back "on." Uncover the photocell and see if the lamp fixture goes "off" again.

E. If possible (and your teacher agrees), turn the lights in the classroom off and see if this causes your lamp fixture to come "on." Turn the classroom lights back "on" and see if this causes your lamp fixture to go "off."

Note: If properly constructed and adjusted, your lamp fixture should come "on" when the photocell is dark; the lamp fixture should go "off" when the photocell is illuminated.

If your circuit does not operate in this manner, check the following:

(1) Check your circuit against the schematic to make sure that your circuit is correctly assembled.

(2) Check for loose connections.

(3) Check to make sure both batteries are delivering their rated load voltage.

(4) Potentiometer -- Substitute potentiometer of different resistance ratings. This will often cause the circuit to operate.

5. Demonstrate the operation of your circuit for your instructor.

6. Disassemble your circuit and return supplies and equipment to storage. Remember, do not discard the device packages.

7. Answer the following discussion questions:

a. What is the function of the control circuit in this application? Which components make up the control circuit?

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b. What is the function of the load circuit in this application? Which components make up the load circuit?

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c. What are the functions of the transistor's base, collector and emitter?

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d. Explain the operation of the light controlled switch.

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