Here is a simple, chargeable leakage and continuity tester that can be operated in two modes: normal mode and gain mode. The gain mode is especially useful for detecting small leakages in electrolytic capacitors or large resistors, which can’t be detected by ordinary continuity testers without amplification of the continuity current. The normal mode is used for continuity testing.
Continuity tester circuit
Fig. 1 shows the circuit of leakage and continuity tester. The use of a rechargeable battery (3.6V, 60mAh Ni-Cd) makes the instrument so compact and lightweight that it can be easily housed inside a glue-stick tube.
Amplification of current continuity is achieved by using a transistor along with small base resistor R1 (1-kilo-ohm) such that its contribution in the closed circuit is small. Resistor R2 (100-ohm) in combination with signal diode D1 limits the charging current and direction.
The battery can be charged through the probes by connecting them to a 5V source. Use a transparent red LED (LED1) for easy detection of continuity.
To check the leakage, flip S1 towards gain mode, clip the alligator clip to one terminal of the component under test, and touch the probe to the other terminal of the component. If LED1 glows, it indicates leakage.
Similarly, to check continuity, flip S1 towards normal mode. Clip the alligator clip to ground terminal of the circuit and touch the probe to the terminal that you want to check for continuity/shorting. If LED1 glows with high intensity, it indicates continuity.
Continuity & testing
The proposed arrangement for this leakage and continuity tester is shown in Fig. 2. First, in the glue stick tube, make the necessary holes and a rectangular slot for the positive probe tip, LED1 and single-pole double-throw switch (SPDT) S1, respectively. Complete the entire wiring, except for the alligator clip and the switch, as shown in the schematic diagram.
Pull the wires for the alligator clip and the switch outside the glue-stick tube and then finish their soldering. Fasten the switch to the glue-stick tube. Similarly, fasten the positive gel-pen probe tip and then LED1 as shown in Fig. 2. The insulation card can be made from any thick paper or plastic (recommended) in round shape with a slot to pass wires through it. Now your leakage and continuity tester is ready to use.
The article was first published in June 2010 and has recently been updated.