Simple Component and Continuity Tester

This simple project may be used for testing components, as well as checking circuit board tracks, wires and connections for continuity (conduction). It tries to pass a small current through the item being tested and the LED will light brightly, dimly or not at all according to the resistance of the item:

* LED bright means the resistance is low, less than about 1kohm
* LED dim means the resistance is medium, a few kohm
* LED off means the resistance is high, more than about 10kohm

When not in use the 9V PP3 battery should be unclipped or the crocodile clips attached to a piece of card or plastic to prevent them touching. You could add an on-off switch in the red wire from the battery clip and this may be the best option if you mount the simple tester in a box.


Parts Required

If you think this project is too simple to be useful, please see the table of components which it can be used to test and think again!

* resistor: 390ohm
* red LED 5mm diameter, standard type
* battery clip for 9V PP3
* crocodile clips: miniature red and black
* stripboard: 5 rows × 7 holes

Testing stripboard, PCB tracks, wires and connections

Circuit diagram for simple tester

Circuit diagram


Connect a crocodile clip on each side of the suspected fault:

* LED bright means there is a connection.
* LED off means there is no connection.

If you are testing a stripboard or PCB which has components soldered in place, beware of possible connections via the components and allow for this when interpreting the results.

Stripboard circuits can suffer from two common problems: solder bridging between adjacent tracks making a connection where there should be none, and tracks broken with a track cutter which have an almost invisible thread of copper conducting across the break.

If a PCB has etched poorly the tracks may be very thin in places or there may be traces of copper bridging between adjacent tracks.

Wires and connections may be checked for continuity (conduction).