PAGE 139 OF 150 · PROJECTS
Build a Simple Continuity Tester
An LED lights when a path conducts.
LED SYMBOLTriangle points from anode to cathode; the arrows show light leaving the part.
What it does
A continuity tester lights an LED when two probes are joined by a complete conductive path, such as a wire or a closed switch.
Circuit
- Two AA cells or a 3 V cell.
- A red LED with a 100 ohm resistor, giving about 10 mA.
- Two probe leads in series with the LED.
Safety
Use it only on circuits with all power removed. Never connect it to mains, and discharge capacitors before testing.
REMEMBER
Test only unpowered circuits.Try it yourself
Sketch the circuit on paper first, calculate the values, then build it on a solderless breadboard using a low-voltage supply. Measure with a multimeter before you make anything permanent.
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