Multiple Continuity Tester(MAX4322)

2016-01-27 06:06  
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This article describes Multiple Continuity Tester (MAX4322). 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: MAX4322.

The continuity tester is a handy adjunct to an ohmmeter. The unit or component whose continuity is to be checked is connected between terminals E1 and E2 (which may be probes or croc clips). The test current then flowing through the unit/component on test causes a potential drop across resistor R2, which is applied to the non-inverting input of buffer IC2. The output of the op amp is applied to transistor T1, in the emitter circuit of which there are a number of parallel-connected light-emitting diodes. EachLEDis in series with a zener diodes and a resistor. The zener diodes have dissimilar zener voltages as shown in the diagram. When the drop across R2 exceeds the sum of base-emitter voltage of T1, a zener voltage, and the threshold voltage of theLEDin series with that zener diode, the relevantLEDlights.

Figure:1 Circuit diagram

Figure 1 Circuit diagram

The diagram shows at which resistance value of the unit/component on test a particularLEDlights. Bear in mind, however, that these values depend to some extent on the type ofLED, and also that the zener voltages are subject to tolerances. Serious deviations may be corrected by the addition of a standard diode or a Schottky diode. It is also possible to add branches to individual requirements, or to use a bar display instead ofLEDs. It is important that the op amp used has a rail-to-rail output since the input voltages as well as the output may rise to the peak supply voltage. This requirement is met by the MAX4322 as used in the prototype.



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