Skill Tester Prototype

Before you solder the parts together on the PCB (Printed Circuit Board) you should first trial your the circuit on a breadboard. When ever I design a PCB I first trial it on a breadboard and make any modification to connections or parts prior to laying out the coper tracks in the PCB design software.


  1. Identify all part from parts list bellow except Q1 – SCR 106D, and J1 – Piezo Buzzer.
  2. Collect Q1 and J1 from teacher as these are not standard parts in the breadbaord kit.
  3. Do not power circuit until it is complete
  4. Assemble circuit on breadboard using the Fritzing Breadboard layout and schematic diagram bellow.
  5. Power circuit and briefly touch the orange and blue wires together
  6. The Piezo buzzer should go off and the LED should turn on. To reset the circuit press the push button switch.

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
  • Ensure SRC is facing the correct direction more details bellow (silver plate towards bottom of breadboard image).
  • Check battery voltage with multimeter in Volts DC mode (should be above 4V)
  • 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.

Information about SCR106D

SCR 106D Picture

The SCR is not a standard transistor but does have some similar properties. The main differance being that when a small charge is applied to the Gate (Pin 3), electricity is allowed to flow from the Anode (Pin 2), to the Cathode (Pin 1). The device lock into this “on” state even if there gate is no longer connected. In our circuit this mean that the buzzer and LED will stay on until the push button switch is pressed to reset the circuit.

Please see full detail on this device in this Datasheet.

Note: the device in the Fritzing image is a standard NPN transistor beacause the part does not exist in the Fritzing parts library.

Parts List

Part Qty Name
VCC1 1 4.5V – 6V Battery Supply
R1 1 330 Ohm Resistor
R2-3 1 1k Ohm Resistor
LED1 1 Red LED 5mm
S1 1 Push Button Switch
J1 1 Piezo Buzzer
Q1 1  Silicon Controlled Rectifier 106D

Fritzing Breadboard Layout and Schematic Diagram

Skill Tester SRC

Skill tester Schematic


More resources:

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