The Capacitor – Flasher

The Capacitor is a little bit like a battery as it is used to store and release electricity. They are generally used in circuits for two main functions:
1. As a filter – When AC signals are directed to a capacitor it takes a certain amount of time to charge and discharge resulting in a more consistent voltage on the other side of the capacitor.
2. As a timer – When a capacitor is used in a circuit with a resistor you can use an equation to predict the amount of time the capacitor will take to charge and discharge. By selecting specific values you can make basic timing circuits.



  1. Identify all component needed in the parts list bellow
  2. Use the Breadboard layout and Schematic diagram to connect all components except battery power supply.
  3. Double check all components are in the correct location and orientation (especially capacitors, transistors and LEDs)
  4. Connect power supply. If circuit works check components do not get hot. If circuit does not function disconnect power supply and diagnose problems.
  5. When circuit is flashing at an even rate try swapping the capacitors with the smaller 10uF Electrolytic Capacitors.
  6. Next try adding an extra 10K or 22K resistors in series to the negative side of the capacitor
  7. Record your finding in your 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
R1-2 1 330 Ohm Resistor
R3-4 1 22K Ohm Resistor
D1 1 Diode 1N4001
LED1 1 Red LED 5mm
LED2 1 Green LED 5mm
Q1-2 2 NPN Transistor BC546
C1-2 2 100uF Electrolytic Capacitor

Fritzing Breadboard Layout and Schematic Diagram:

Note: the following circuit uses transistors with a CBE pin configuration (please ensure you are using BC546 transistors (see transistor page for more details).

Capacitor Breadboard CircuitFlasher Schematic Diagram Fritzing


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