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.