The Resistor – Dimmer Circuit

The Resistor is probably the most commonly used electronic component and comes in a variety of values, shape, size, and style. Some resistors have set values whilst others can be variable for particular applications. The following video will talk about what resistors are used for and how to determine their value.



  1. Identify all of the parts required for all three circuits bellow in the parts list:
  2. Before starting ensure power supply is not connected
  3. Use the Fritzing Breadboard Layout and Schematic Diagram images to connect the components with prototyping wires to complete “Circuit 1 – 10K Resistor”.
  4. Take note of the LED brightness before replacing 10K resistor with alternate such as 330 Ohm, and 1K resistor.
  5. Repeat steps 2 – 3 to create “Circuit 2 – The Potentiometer”
  6. Rotate the knob on the Potentiometer and observe the LED
  7. Repeat steps 2 – 3 to create “Circuit 3 – The LDR Dimmer”
  8. Cover the Light Dependent Resistor (LDR) so that less light hits the surface of the device. (Note: it is not touch sensitive, but less light will hit the surface when you touch it)
  9. Record findings in learning journal.

Diagnosing problems:

  • If any component is getting hot disconnect the battery.
  • Ensure a resistor is used in the circuit or LED will be burned out and damaged
  • Ensure LED positive leg (longest) is connected to positive side of circuit
  • Check battery voltage with multimeter in Volts DC mode
  • Try a different LED in case it has been burned out (ensure you are using a resistor!)
  • Look at breadboard picture bellow and ensure all connection are correct.

Parts List:

Part Qty Name
VCC1 1 4.5V – 6V Battery Supply
R1 1 330 Ohm Resistor
R2 1 1k Ohm Resistor
R2 1 10K Rotary Potentiometer
R3 1 Light Dependent Resistor (LDR)
LED1 1 Red LED 5mm

Fritzing Breadboard Layouts and Schematic Diagrams: 

Circuit 1 – 10k Resistor:10K Dimmer LED10K Dimmer Schematic

Circuit 2 – The PotentiometerPot Dimmer BreadboardPot Dimmer Schematic

Circuit 3 – The LDR DimmerLDR Dimmer BreadbaordLDR Dimmer Schematic

Colour Chart:


Extra Teaching Material:

  • Discuss where you might find a potentiometer around the home
  • Discuss where you might find an LDR around the home
  • Use multimeter (set to DC volts) to measure voltage across LED with different resistor is Circuit 1
  • Use multimeter (set to DC Amps) to measure voltage across LED with different resistor is Circuit 1


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