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IC 555 based Capacitance Meter

Last Updated on by 83 Comments

In this post we will talk about a couple easy yet very handy little circuits in the form of  frequency meter and capacitance meter using the ubiquitous IC 555.

How Capacitors Work

Capacitors are one of the main electronic components which come under the passive component family.

These are extensively used in electronic circuits and virtually no circuit can be built without involving these important parts.

The basic function of a capacitor is to block DC and pass AC or in simple words any voltage which is pulsating in nature will be allowed to pass through a capacitor and any voltage that’s not polarized or in the form of a DC will be blocked by a capacitor through the process of charging.

Another important function of capacitors is storing electricity by way of charging and supplying it back to an attached circuit by the process of discharging.

The above two main functions of capacitors are used for implementing a variety of crucial operations in electronic circuits which enable getting outputs as per the required specifications of the design.

However unlike resistors, capacitors are difficult to measure through ordinary methods.



For example, an ordinary multitester might have many measuring features included like an OHM meter, voltmeter, ammeter, diode tester, hFE tester etc. but might just not have the illusive capacitance measuring feature.

The feature of a capacitance meter or an inductance meter is seen to be available only in high-end type of multimeters which are definitely not cheap and not every new hobbyist might be interested in procuring one.

The circuit discussed here very effectively tackles these issues and shows how to build a simple inexpensive capacitance cum frequency meter which can be built at home by any electronic novice and used for the intended useful application.

Circuit Diagram

How Frequency Works to Detect Capacitance

Referring to the figure, the IC 555 forms the heart of the entire configuration.

This work horse versatile chip is configured in its most standard mode that is the monostable multivibrator mode.
Every positive peak of the pulse applied at the input that is pin #2 of the IC creates a stable output with some predetermined fixed period set by the preset P1.

However for every fall in the peak of the pulse, the monostable resets and auto triggers with the next arriving peak.

This generates a kind of an average value at the output of the IC for which is directly proportional to the frequency of the applied clock.

In other words the output of the IC 555 which consists of a few resistors and capacitors integrates the series of pulses to provide a stable average value directly proportional to the applied frequency.

The average value can be easily read or displayed over a moving coil meter connected across the shown points.

So the above reading will give a direct reading of the frequency, so we have a neat looking frequency meter at our disposal.

Using Frequency to Measure Capacitance

Now looking at the next figure we can clearly see that by adding an external frequency generator to the previous circuit, it becomes possible to make the meter interpret the values of a capacitor across the indicated points, because this capacitor directly affects or is proportional to the frequency of the clock circuit.

Therefore, the net frequency value now shown at the output will correspond to the value of the capacitor connected across the above discussed points.

That means now we have a two in one circuit which can measure capacitance as well as frequency, using just a couple of ICs and some casual electronic parts. With little modifications the circuit can be easily used as a tachometer or as RPM counter equipment.

Parts List

R1 = 4K7

R2 = 47E

R3 = CAN BE VARIABLE 100K POT

R4 = 3K3,

R5 = 10K,

R6 = 1K,

R7 1K,

R8 = 10K,

R9 = 100K,

C1 = 47n,

C2 = 100n,

C3 = 100n,

C4 = 33uF/25V,

T1 = BC547

IC1 = 555,

N1---N6 = IC4049

M1 = 1V FSD meter,

D1,D2 = 1N4148

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Reader Interactions

Comments

      • Hi Swag thks for response. I was going to build Brighthub circuit but noticed it’s a bit different. This circuit is more modern? Do you have a pcb for it? Thks.

        Reply

        • You are welcome Andrew, I am sorry I do not have a PCB design for this, I wish I could do it for you, however due to lack of time I am not able to do it at the moment…

          Reply

          • Hi Swag ok I did this circuit. The thing is that I using a volume audio meter don’t know if this is good? Cause when I tried it nothing came.

            Reply

            • Andrew, the recommended meter is 0-1V FSD moving coil meter, not sure how other meters might work…. this circuit has been thoroughly tested by me.

    • I am sorry a DMM will not work correctly, because the output could be in a continuously vibrating mode which may be efficiently countered only by a moving coil meter

      Reply

  5. Dear Mr Swagatam,
    Do you have a schematic about ESR meter. Technicians recommend me to check the electrolytic first everytime I come up with a dead circuit, But I dont know how to measure it. Thank you in advance for your answer.

    Reply

    • hello Tanmay,

      1V is the recommended one, for other higher voltages you may need to reduce R7/R8 proportionately for getting the deflections.

      Reply

  8. Hello sir, will deflection shows for almost ranges of pF, nF, uF,…..
    Another: sir may u pls reffer about components in above diag. mainly upon which quantity of deflection depends?

    Reply

    • Hello Ramkumar, the range will need to be calibrated by appropriately setting or selecting the value of R3.

      please refer to the following article to know more details about the components and the functioning:

      easy-electronic-circuits.blogspot.in/2014/02/simple-tachometer-circuit-or-revolution.html

      Reply

  10. dear sir,
    i try to make this circuit in practical . but fails to get any output deflection on fsd when capacitance is applied. please tell me how to rectify the problem.
    i am getting 2.2 mv in at FSD and 7.8 mV at unknown capacitance side.
    please tell me the range of above meter also.
    please reply soon.
    I am struck.

    Reply

    • Dear Renu,

      Use a 100k pot in place of R3 and adjust it for calibrating the scale of the connected meter. I have tested this circuit and it worked well for me.

      Reply

    • Sir,
      I cant find the solution. its not working. R3 didn't help me.
      i wanna share my circuit photograph with you. Please suggest some other option for rectifying my problem. I am using voltmeter as FSD meter.
      What is the range of this circuit.
      Give me another alternative to talk to you for rectifyng my problem.
      i will be highly obiliged.

      thank you for your prompt respose.

      Renu

      Reply

    • which meter have you used at the output? you must use a 0-1V FSD moving coil type meter.

      The frequency range is 10Hz to 10kHz

      You can send the pictures to my iD hitman2008@live.in

      Reply

    • I am using digital multimeter for this. As i want to know the correct of voltage output.
      I am getting output but its showing me almost same value for most of the different capacitor.
      I want to mesure nF capacitance can it be possible with your circuit?

      Reply

    • try different value capacitors and try to find the corresponding full scale range of the meter, you can also take the help of R3 by adjusting it to locate the range of the meter which corresponds to the capacitor value.

      yes nF can be measured with this meter, according to me only moving coil type meters will work correctly here, i am not sure about DMMs.

      Reply

  12. Thank you very much sir, but how will i know about your newly posted article ? Where should i have to search ??
    I request you to construct a one having range of 1 to tens or hundreds of Mhz with seletable frequency ranges using common ics such as CD4040,4017,555 etc but excluding the use of programmable chips. The circuit should also be capable of measuring accurate frequencies. I am requesting such an accuracy since i have faced slight to serious variations of known frequency levels ( which may have occured due to variations in the duty cycle of the waves, inability to detect high voltage peaks of the signal by the ics due to poor signal conditioning etc. )

    Reply

  13. Sir could you please suggest a suitable frequency divider circuit which can be used in corporation with a digital fequency meter ( which is capable of measuring a maximum of 999 Hz )to measure upto tens or hundreds of MHz by caliberations.
    The divider should have this range
    f/10 to f/10,000 indicated by respective frequency ratio switches

    Reply

  14. Sir i have tested the basic circuit diagram without connecting any galvanometer or binary indicator. On measuring voltages by feeding a 1 Khz wave, i got approx. 0.12 avg. Voltage. On feeding 10 Khz i got 0.4V etc. I understood that voltage increases on increase in freq. But the problem is , very small voltages in small frequency. Actually i want to make such a frequency meter which can be used to measure atleast 50 hz and therefore can be used for the testing at various construction steps of inverter like projects. I don' t need a one with LED displays. I am interested in implementing the above circuit with IC LM3914 but what to do at that lowest voltage levels???? Will U PLZ HELP ME????

    Reply

    • Nazriya, the above circuit can be used to measure right from 10Hz to 10kHz….you will have to adjust R4/R5 also appropriately for the different ranges of the frequencies…the circuit will not work with a single setting for all the ranges as is true for even highly sophisticated instruments.

      By the way the LM3914 just needs 1 to 5V as input for providing the desired output display, in fact you can tweak the input preset of the LM3914 even to sense voltages as low as 0.2V

      Reply

  15. Sir if i am gonna use an LED dot indicator using IC LM3914, will it perfectly function as a frequency meter on better caliberations???
    Actually what change is fed to the galvanometer leads in the circuit provided by you??? Is it a voltage change in accordance with frequency???? I am asking you this, because i will be able to implement the ic instead of galvanometer iff voltage fed to it is varied…… The biggest doubt having is, WHETHER THE OUTPUT VOLTAGE AVAILABLE FROM THE IC 55 WILL BE ENOUGH TO DRIVE THE IC3914?

    Reply

  16. Sir can i use a voltmeter found in submersible pump ( showing reading upto 300 V) be used after any suitable calliberation since 1 V FSD meter is not available in our area.
    If it can't be done, can you please tell me how to employ a binary readout in place of this meter to measure frequency. I have the following ics with me
    4026,4011,4017,4047,4007 and a few 555 and 556 ics and 741 opamps

    Reply

    • Nazriya, I don't think that would be feasible, because such voltmeters would have a coil with very high no of turns, not possible to modify them

      A different simpler approach could be to use a LM3915 IC for getting an LED bar graph readout

      Reply

  17. Sir i have found a simple digital freq. meter in the following link. Please just check it out…

    www.eeweb.com/blog/circuit_projects/1hz-to-1mhz-frequency-meter-with-digital-display

    But the 4 Bit microcomputer ic 4583 is not readilly available anywhere. Can i substitute it with a 4 bit single chip microcomputer ic LC6520

    Reply

  18. Dear Swagatham,
    First of all i am congradulating you for this blog being a good success. The peoples like me who are just beginners in electronics can make use of many innovative ideas from here.
    Now i am coming into the subject. I have read this article and impressed much. But it would have been better to modify this with a digital reader using 4 no.s of seven segment displays instead of the analog set up. Can u please help me?

    Reply

    • Dear Subramanyam,

      Thank you very much! Yes It's possible to get a digital readout from the above circuit, we can do it by integrating the following circuit with it:

      https://homemade-circuits.com/2013/05/make-this-simple-digital-voltmeter.html

      Reply

  19. Hello sir,
    I had tried to make the above circuit for capacitor meter.i had used old vu meter for 1v fsd meter.but when i had tested it with 1uf nonelectrolyte caps its showing me a very little deflection which is not enough to clibrate the scale.and i also want to know the use of r3
    (can be variable 100k )and how it is connected i.e.to use only two tip or to use all three.meter needle is giving vibrating reading.i think r8 should be reduced
    Please help me
    Thanks

    Reply

  21. Hello sir,
    I had made some inverter circuits by following ur blog
    If i have to measure the frequency of them then i had to connect the output of inverter transformer(ie220v) to above circuit via a step down transformer or i had to connect the output of inverter circuits which is going to mosfet's gate directly to above circuits

    Reply

    • Thanks for ur quick reply sir,
      One more thing if i had to measure our mains ac frequency according to u i had to step down it via transformer then what should be the maximum voltage i should connect on the test point of above circuit (i e0 to 12v or 14…)and i had to connect the low voltage side directly to test point or via rectifier and capicitor bridge

      Reply

    • You can make the base resistor to 220K 1/4watt and feed the mains 220v directly across this resistor end and ground….the whole circuit now becomes at mains potential so be cautious.

      Reply

  22. HI swagatam,
    first of all, thank for this great information . before reading this article i was working on a project like this but the idea is slightly different . the idea was to generate a stable clock with a certain frequency using the 555 oscillator in astable mode then measuring that frequency using a micro-controller . for measuring the frequency,it's working properly when tested using a function generator(square wave) . the problem is in the 555 ,it's output frequency is not stable,i.e, value vary rapidly with time with about +/- 5HZ and my application need to be more accurate
    do you have any advices about stabilizing the 555?
    thanks in advance;

    Reply

  23. Hi Swagatam

    While exploring my schematic files I came across this schematic of inductance meter.

    https://dl.dropboxusercontent.com/u/20969135/Inductance%20Meter.gif

    Please check it and let us know if it is that easy to make. What will be the accuracy, can it measure µH ?

    Reply

    • Hi Abu-Hafss,

      some circuits are difficult to analyze in mind and this is one of them, typically because it incorporates an LC frequency network unlike the above which uses an RC, RC frequency circuits are easier to understand…. you can try simulating it in a simulator.

      Reply

    • Helo Avijeet,

      1V FSD means 0-1V full scale deflection.

      A 1V meter can be made into a 220V meter but a 220V meter cannot be modified into a 1V meter.

      Reply

  27. hi,
    can i use digital voltmeter circuit from one of ur older post using 40 pins ic7107 in place of 1v fsd meter to make it didgital frequency meter???

    if yes then how can i do it?

    Reply

    • Yes that can be done for getting a digital reading.

      Connect the output of the 555 circuit to the "voltage IN" of the 7107 circuit.

      Prior to that you will have to adjust the output resistor values of the frequency meter circuit suitably so that it works in the range of 200mV

      Reply

    • 2 ques is still confusing my mind,,

      1: as u said above(Prior to that you will have to adjust the output resistor values of the frequency meter circuit suitably so that it works in the range of 200mV)so,,
      which circuit should works in range of 200mV and how? can u xplain little more

      2:output resistor= R8 of frequency meter circuit= true ?

      thnx

      Reply

    • R7 and R8 both…. as per the shown ratio….R8 is 10 times R7, so if you select R7 as 100K, R8 would become 1M….increasing the value will decrease the voltage proportionately across the "meter" terminals.

      Reply

    • Swagatam

      I have one question regarding using a DVM here. In a coil VM it is easy to calibrate the meter with some pen/marker but, how shall we interpret the displayed voltages on a DVM into Hz? Do we have to multiply the voltages with some constant?

      Reply

  28. hi swagatam,

    i'm interested with this circuit.
    can i use this to get the AC freq.? how is the connection would be?

    regards,

    Reply

  29. Dear Sir,

    First of all thank you for quick reply. I saw that circuit but there is confusion to make this circuit specially about meter and band width. How can I calibrate this type of meter. Its really a simple circuit. Kindly explain it in detail.

    Thanks

    Mubashir

    Reply

    • Dear Mubashir,

      You may do it by supplying a known range of frequency at the input and marking the extreme point of the reading over the meter. Since the reading will be perfectly linear, you could mark the rest of the corresponding points by manually counting the present calibrations over the meter, for example if the end of the meter reads 30kHz, the center of the calibration would be 15khz and so on…

      Regards.

      Reply

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