Wire Continuity Tester (LM709)

2016-01-28 19:45  
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This article describes the Wire Continuity Tester (LM709). The principle is very simple, very practical. The circuit components can help you understand better grasp this principle. For example, in this circuit, you can go to find and buy these components: LM709.

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.


Figure 1 

Indicator of the circuit is aLED. 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 untilLEDbrights. When you separate the probes againLEDwill fade out. This is a cheap and very useful circuit. You can build it on aPCBto use more easily.



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