Wireless mains voltage tester.

john September 22, 2009 19 Comments
Description. This circuit can be used to test whether mains voltage is present or not without having electric contact with mains line. The CMOS IC CD4033 is the heart of this circuit. The CD4033 consists of a 5 stage decade Johnson counter and an output decoder for converting the Johnson code to a 7 segment decoded output for driving 7 segment LED display. A 10cm long insulated copper wire connected to the clock pin (pin1) of the IC serves...
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How to test FET’s-Jfet and Mosfet

jojo September 8, 2009 5 Comments
All the testing methods below uses a multimeter and hence its How to test FET’s especially the JFET and MOSFET using a multimeter. How to test an FET ? FETs are checked by measuring different resistances by a multimeter. When resistance is checked between source and drain, it should be of the order of 10 kohms. How to test a JFET ? When a JFET is checked as a diode (gate-to-channel junction) multimeter should indicate low resistance between gate...
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How to test a thermistor

john March 21, 2011 9 Comments
Thermistors are of two types, NTC (negative temperature coefficient) and PTC (positive temperature coefficient types). As their name indicates the resistance of an NTC thermistor will decrease with temperature and the resistance of a PTC thermistor will increase with temperature. Both PTC as well as NTC thermistors can be roughly checked by using an analogue multimeter. Keep the analogue multimeter in resistance mode. Connect the multimeter terminals to the thermistor leads. Polarity is not an issue here. Now heat...
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How to test a capacitor.

john August 24, 2009 18 Comments
This article shows you how to test a capacitor using analogue multimeter. Firstly short the capacitor leads for discharging it completely. Set the multimeter to high resistance mode. Connect the multimeter terminals to the capacitor leads. For electrolytic capacitors the positive terminal of multimeter must be connected to the positive lead of the capacitor and negative terminal of multimeter to the negative lead of capacitor. For other capacitor types, polarity is not an issue. At the moment you connect...
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How to test an LDR

john January 23, 2018 11 Comments
LDR (light dependent resistance) can be very easily tested by using a digital multimeter. We all know that the resistance of an LDR varies according to the light falling on it. At bright light, the LDR resistance will be around 500Ohms and at darkness the resistance will be around 200K. For a proper diagnosis we need to measure the resistance of the LDR at bright light and at darkness. Test1. Keep the multimeter at Ohms mode. The LDR must...
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Testing a UJT

john July 23, 2009 5 Comments
UJT (Uni junction transistor) can be easily tested by using a digital multimeter.The three steps for testing the health of a UJT are as follows. 1. Measuring the resistance between B1 and B2 terminals. Set your digital multimeter in resistance mode.Connect the positive lead of multimeter to the B1 terminal and negative lead to the B2 terminal.The multimeter will show a high resistance ( around 4 to 10K ). Now connect the positive lead to B2 terminal and negative...
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How to test an SCR

john May 21, 2009 18 Comments
Testing SCR using a multimeter. A multimeter can be used to test SCRs quite effectively. The first procedure is to check the diode action between the gate and cathode terminals of the SCR. This test is just like what you have done in the case of testing a silicon diode (see testing a silicon diode). Now put the multimeter selector switch in a high resistance position. Connect the positive lead of multimeter to the anode of SCR and negative...
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How to test a triac.

john May 18, 2009 14 Comments
Testing triac using a multimeter. A multimeter can be used to test the health of a triac. First put the multimeter selector switch in a high resistance mode (say 100K), then connect the positive lead of multimeter to the MT1 terminal of triac and negative lead to the MT2 terminal of triac (there is no problem if you reverse the connection).The multimeter will show a high resistance reading (open circuit).Now put the selector switch to a low resistance mode,...
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How to test a diode

john May 13, 2014 14 Comments
Diodes are one of the components that can be tested very easily.Ordinary diodes as wells as Zener diodes can be checked by using a multimeter. While testing a diode the forward conducting mode and reverse blocking mode has to be tested separately. Testing ordinary diode using a digital multimeter. To check an ordinary silicon diode using a digital multimeter, put the multimeter selector switch in the diode check mode. Connect the positive lead of multimeter to the anode and...
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