Capacitance meter using LM2917

jacky May 26, 2010 10 Comments

Description.
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.
Circuit diagram.

capacitance meter using LM2917
Notes.

  • The circuit can be assembled on a vero board.
  • Resistor R1 can be used for calibration.
  • Meter M1 should be a 10V FSD voltmeter.
  • The IC must be mounted on a holder.
Comments
  • July 25, 2012

    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

  • June 18, 2012

    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

  • June 15, 2012

    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

  • RICK
    November 11, 2011

    For M1 You can use a 1 m.a. meter and connect a 10K resistor in series with the meter, By Ohm’s Law E=I x R= 1 m,a. x 10K =10 volts. If you need a 5 volt Meter use a 5K resistor( 2 10K resistors in parallel ) All I did here was convert a ammeter into a D.C. Voltmeter. This is a possible solution to the 10V FSD PROBLEM. i WOULD STICK WITH A 555 Timer @ 60 Hz Rather than the A.C. VOLTAGE DIVIDER……..I couldn’t agree more with Steven’s concern on A.C, Voltage Issue,,,,,,,thE 555 Solution is a much safer alternative!!!! Why not try using a step down transformer around 8 to 12 vac??? Good Building and Stay Safe!!!

  • Kevin Lee
    May 29, 2010

    This is a question to Steven.
    Can you publish a suitable circuit for a “practical” capacitance meter?
    Thank’s
    Kevin

  • Kevin Lee
    May 29, 2010

    I have the same question as Edgardo and Victor.
    Thank you.

  • seetharaman
    May 27, 2010

    Hi FSD means full scale division. that is you have to use a 0 to 10 volt range meter. you can use any good DMM in 10 volt full range ( 0 to 1.99 volt in a 3 and half digit multimeter or a DVM)
    refer to manufacturers data sheet and application for pin connection details
    http://www.datasheetcatalog.org/datasheet/nationalsemiconductor/DS007942.PDF

  • Steven Gendron
    May 27, 2010

    I am worried by the indication in the schematic of a direct connection to the live mains. This is extremely dangerous when done by a novice circuit builder. Much safer is to derive the 60 Hz clocking reference from the lower voltage secondary winding of the power supply that is used to feed the 15 volts DC working voltage to the LM2917. Resistors R3/R4 form a 10:1 mains voltage divider so 8 to 12 volts AC could be applied directly to pin 1. An alternate application would be to use a LM555 as a cheap 60 Hz oscillator.
    The term FSD means simply “Full Scale Deflection” and is mostly meaningless in the modern era of digital readouts. As presented, this circuit is only of educational value and not a practical capacitance meter for the workshop.

  • Victor Sedere
    May 26, 2010

    I also have the same question raised by Edgardo.
    In addition, what is that indication of 15V DC connected with pin 5&6 of the IC?
    Can you give an idea to use it for higher value capacitors?
    Do you have simple circuits similar to this to measure inductance?
    Thank you.

  • Edgardo Diolola
    May 26, 2010

    In this circuit, what do you mean by thE 10V FSD?, I mean FSD only.
    How can I coonect this to 220V AC supply?

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