# Capacitance meter using LM2917

Posted on Feb 5, 2014

The circuit diagram of a simple capacitance meter using IC LM2917 is shown here. The LM2917 is a high gain monolithic frequency to voltage converter IC from National Semiconductors. Even though the main application of LM2917 is in tachometers, it can be also used for a variety of applications like this. Capacitance values from 0. 01uF to 0. 1uF can

be measured using this circuit. The capacitance to be measured is connected between pin 2 of the IC and ground. The output voltage available across resistor R2 will be proportional to the Cx and it will be displayed by the meter. Resistor R1 can be used for calibrating the circuit. I think that something is missing in the diagram, I might not be a electronic wizard, but how is possible that you connect R3 50k to the line input R3 goes to the first pin of IC LM2917 the IC will blow up, on your face. If you look carefully you see that pins 5, 6 of the IC go to 15VDC supply. That means that we have to insert a power transformer in my case of 125vac;with a secondary of 18vac at line input 110vac 60HZ;then use a rectifier bridge and all that stuff to rectify and clean every peak of the ac converted to dc The input of the 110 VAC 60 HZ; a step down transformer should be used, 18-20vAC output, then a bridge rectifier and the proper electrolytic capacitors to filter the remain AC;the problem is he didn`t include that information and we don`t know the values of those components I see that the other side of R3 is connected to 110 V AC 60HZ ;if I connect it to the AC line the tester will blow on my face;it have to be an error;there is not a step down transformer to bring the line to 15-18 V Ac and then a rectifier circuit to bring it to clean DC For M1 You can use a 1 m. a. meter and connect a 10K resistor in series with the meter, By...

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