Quantity   Component name
1 × D1, LED, T1-3/4, Red or Green or Other LED for power-on indication, hole diameter: 0.711 mm (.028")
1 × D2 or D3, LED, T1-3/4, Green or Red or Other LED for discontinuity/continuity indication, hole diameter: 0.711 mm (.028")
1 × R1, Resistor, Axial, ~1/4W, 50-1000 Ohm depending on power supply, LED Current-limit resistor for D1
2 × R2, R3, Resistor, Axial, ~1/4W, 470-20000 Ohm, noncritical value Pullup resistors
1 × R4, Resistor, Axial, ~1/4W, 50-1000 Ohm depending on power supply, LED Current-limit resistor for D2/D3
2 × S1, S2, Switch, Toggle, SPDT Board hole diameter: 2.1 mm (.083"), pin spacing 4.7 mm (.185”)
1 × U1, IC, ULN2003A, Darlington Transistor Array, DIP16 Package
1 × O+/O-, Beeper/Buzzer, DC input compatible with power supply voltage Board-mount pin spacing: 7.62 mm (.300"), hole diameter: 0.9 mm (.035")
1 × I+/I-, Tester Inputs, Banana Plugs or Other Remotely mounted -- wired to the PCB
1 × V+/V-, Power Supply 5 V (3-12V), wired to the PCB