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Return to BlogWire Continuity Tester by LM709
Posted Jan 26, 2012 at 1:22 pm
Figure 1
Wire Continuity Tester : While detecting discontinuities on a circuit board, it is probable to include resistors, semiconductors or other elements in measurements. This situation may cause wrong results. On the other hand sometimes the voltage or current of the multimeter may defect some circuit components.
Our circuit overcomes this inconvenient conditions. The circuit determines greater than 1 ohm values as discontinuity. Measure voltage is not more than 2mV. So no kind of diode, IC or other component is bypassed. Maximum current output of the circuit is about 200uA.
Indicator of the circuit is a LED. Voltage supply may be two 9 Volt batteries.
Voltage adjustment of the amplifier is done by P1 potentiometer. To do this process, first short circuit the probes and then turn P1 until LED brights. When you separate the probes again LED will fade out.
This is a cheap and very useful circuit. You can build it on a PCB to use more easily.
Comments on this post:
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3 years ago: dear sir
i need a small wire harness tester. in which i can test the continuity and short points. no of ports can vary from 2-40.
if you have any tester compatible to my requirement or you can suggest any circuitry for the same then please help.
i am in urgent need of this kind of tester.
thanks & regards
parveen legha
3 years ago: Respected sir.
Can there be any cheaper and less problematic circuit which gives sound and light output when testing continuity and testing the components?
Please help me in preparing and distributing them to the students of a nearby electronics college, which they are in need of!
thanks a lot
2 years ago: yes indeed, it was easy to build! thanks very much sir!
2 years ago: I noticed that there is a large requirement for the batteries because it uses two 9V batteries. I guess we can reduce this like putting 2 AA batteries...