Digital voltmeter using ICL7107

Description.
The circuit given here is of a very useful and accurate digital voltmeter with LED display using the ICL7107 from Intersil. The ICL7107 is a high performance, low power, 3.5 digit analog to digital converter. The IC includes internal circuitry for seven segment decoders, display drivers, reference voltage source and a clock. The power dissipation is less than 10mW and the display stability is very high.

The working of this electronic circuit is very simple. The voltage to be measured is converted into a digital equivalent by the ADC inside the IC and then this digital equivalent is decoded to the seven segment format and then displayed. The ADC used in ICL7107 is dual slope type ADC. The process taking place inside our ADC can be stated as follows. For a fixed period of time the voltage to be measured is integrated to obtain a ramp at the output of the integrator. Then a known reference voltage of opposite polarity is applied to the input of the integrator and allowed to ramp until the output of integrator becomes zero. The time taken for the negative slope to reach zero is measured in terms of the IC’s clock cycle and it will be proportional to the voltage under measurement. In simple words, the input voltage is compared to an internal reference voltage and the result is converted in a digital format.

The resistor R2 and C1 are used to set the frequency of IC’s internal clock. Capacitor C2 neutralizes the fluctuations in the internal reference voltage and increases the stability of the display.R4 controls the range of the voltmeter. Right most three displays are connected so that they can display all digits. The left most display is so connected that it can display only “1” and “-“.The pin5(representing the dot) is connected to ground only for the third display and its position needs to be changed when you change the range of the volt meter by altering R4. (R4=1.2K gives 0-20V range, R4=12K gives 0-200V range ).
Circuit diagram.

Notes.

  • Assemble the circuit on a good quality PCB.
  • The circuit can be powered from a +/_5V dual supply.
  • For calibration, power up the circuit and short the input terminals. Then adjust R6 so that the display reads 0V.
  • The ICL7107 is a CMOS device and it is very sensitive to static electricity. So avoid touching the IC pins with your bare hands.
  • The seven segment displays must by common anode type.
  • I assembled this circuit few years back and it is still working fine.

Show Comments

78 thoughts on “Digital voltmeter using ICL7107

  1. FUTURE

    how to connect the capacitor 6 and capacitor 7 in led display digital voltmeter circuit of smart kit 1137

    Reply
  2. bbbb

    This voltmeater is working precisely.
    Thanks!!
    Can you help me with a schematic diagram of a digital meter that can measure ampere(0A-20A) pls..

    Reply
  3. Nishant

    I assembled the circuit, but only third 7seven segment is glowing, rest are glowing with very low brightness and its unreadable. Help me please.

    Reply
  4. Richman

    Somebody pls tell me… Does the tolerance of the capacitors used matter?? And how will it affect the circuit??

    Reply
  5. Mile

    Are you shure that decreasing the value for R4 you increase the range? By my logic, I shoud be in the oposit… I want to make an amperpeter, I need the smallest range (0-2V). I completly removed R4, but it is not working linearely… Anybody tryed to use the 0-2V range? please tell me how you fixed this issue. Thanks!

    Reply
    • Seetharaman

      R5 and R4 are input potential divider. if you remove R4 200mV will be input range by reducing R4 you can achieve higher ranges. C1 C2 C3 C4 R2 and R3 are to be close tolerance components if not the measuring error will be high.

      Reply
  6. Kedar

    I implemented this ckt on a MATRIX PCB but when i give input i dont get desired o/p . the o/p just shows 166.6 everytime. even if i dont give i/p it shows 166.6 do i have to give separate power supply of -5V to pin 26 coz i’ve given +ve terminal to pin 1 and -ve terminal to pin 26 from the power supply. plz plz help me. suggest everything possible…..plz

    Reply
  7. omooh

    pls, how can this be wired up to measure ac voltage or you can help me with a schematic diagram of a digital meter that can measure dc voltage(1000 volt0 and ac voltage (up to 700 volt)

    Reply
  8. subhendu

    if the value of R1 is not accurate , can there have any problem to measure accurate voltage?
    Please anyone help me.Thank you.

    Reply
    • Seetharaman

      R1 is for the decimal point indication, hence no relevance on the measurement of voltage. In the above circuit the maximum reading can be 199.9

      Reply
  9. salim

    thank you publish Digital voltmeter using ICL7107 simple circuit
    easy drawing thank for publish. we want more popular easy circuit.
    pleas write analog maximum in put voltage?

    Reply
  10. CHINNA

    There is given for DC voltage measurement,is it possible to measure for AC also or any modifications are required please give me suggestion

    Reply
    • ANEESH M

      PIN NO 5 IS CONNECTED ACCORDING TO THE RANGE OF VOLTMETER IF YOUR VOLTMETER
      RANGE IS 200V CONNECT PIN 21 OF IC TO D4 DISPLAY IT IS FOR SHOWING DECIMAL POINT IF THE INPUT IS 2OOV THE READING SHOWS 199.9V

      Reply
  11. seetharaman

    Hi Rohit the basic meter is designed to measure 0 – 199.9 mV D.C. range. Modify it to accept 0 to 1.999 volt by using suitable multiplier. Convert current into mV by using a suitable conditioning resistance to measure D.C. current. For 0 – 1.999Amp as 0 – 1.999 volt 1 ohm 5 watt conditioning resistance. if you feel this drop is high use 0 – 199.9mV range with 0.1 ohm 1watt resistance and suitably shifting the decimal point.

    Reply
  12. seetharaman

    Hi Rohit Kumar you can try with Vega Kits Mumbai. Go through the site indicated by Patrick Vaz down load PCB design and order with a PCB maker.

    Reply
  13. Rohit Kumar

    Hi Seetharaman,

    Can you pls design a PCB for this lovely Circuit, or if you have one already,where can i download the same.

    Thanks in anticipation

    Reply
  14. vikas

    no my circuit works actually my preset is loose that is y im getting varying value i write last comment for varying value
    circuit is working properly i hav problem in proper calibration coz im new.
    change resistance and capicator acording to datasheet of ic and ur ckt will actually run dont follow this ckh values

    Reply
  15. vikas

    not working properly i even cange all value of resistance and capacitance from datasheet but still got varying values any one can help….

    Reply
  16. ARTOIS

    HI JOJO, I REDID THE POWER SUPPLY WITH -5V +5V NOW ITS WORKING PERFECTLY.I REDID THE PCB AND ANYONE INTERESTED IN IT CAN E MAIL FOR IT AT ejhgbb@gmail.com
    im still trying to figure out how to get the forums page as ive been a member of ur site must be at least a year now

    Reply
  17. ARTOIS

    HI JIM I SEE U BUILT THIS CIRCUIT AS I ALSO DID WITH 7805 7905 BUT IM FEEDING IT WITH A NORMAL POWER SUPPLY 16V-0V. IT THINK THIS IS WHERE IM WRONG CAN I ADD A PCB IMAGE ON THIS WEB SITE
    TXZ JOHN

    Reply
  18. mahamoud

    pls help me as soon as possible

    1.What is the recommended input voltage which is connected in R5 (pin numbers 30 and 31?.
    2. is R4(12K) is compulsory to the circuits? if i make it short-circuited or open-circuited what will happen?

    please reply quicly

    Reply
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  20. Jim

    I sent an email listing all of the errors and omissions I found when building this voltmeter which I thought would be useful to the constructors who were having problems but someone has edited them out of my comments, why ?

    Regards
    Jim

    Reply
  21. Jim

    Built this cct yesterday and it works really well.
    There are some omissions on the dwg
    Power supply used 230v/10-0-10 mini tx with 7805 for +5v and 7905 for -5v plus usual resistors, capacitors and protection diodes.

    For switching ranges used 4 pole 3 way rotary switch, first pole changes resistor and second pole moves decimal point ( pin 5 on indicator ) from D1 at 0-2v DC to D3 ie 0-200v DC.
    For calibration short input and wind 20K pot until the reading is JUST 000 and calibration is spot on on all ranges with good stability.
    For 4.6 euros and a few bits from the spares box not a bad instrument, well worth building. Use RS website for data sheets. Cheers, Jim

    Reply
  22. Ed

    Hi, with so many complaints of thsi circuit I think I might not should trust this electronics engineeeeeeeeer! I beeternot build this,,NO?

    Reply
  23. Ojong

    Hi every one
    i’m trying to implement time correction in a clock i am building. I need help on this. i have the clock running already but i need the user to be able to regulate it if he chooses to
    I will be grateful for an answer

    Reply
  24. KINHO

    Olá amigo,

    Como achar o componente ICL7107 no EAGLE,estou montando um termomêtro no eagle com esse componente e não estou encontrando.

    Aguardo uma ajuda……………..ok..Kinh0

    Reply
  25. John

    another site created the same.. but more explanation and proper connection.

    http://english.cxem.net/izmer/measured18.php

    I’m constructing the circuit in EAGLE and found these problems.

    1.) the PIN1 of IC and R7 should be connected to +5v.
    2.) 3rd 7-segment should have the PIN5 connected to 560ohms.
    PIN5 is the decimal point!! the reading will be 1000v+ in this circuit.

    Reply
  26. zernab

    Hi, for R4=0(shorting of pin 30 and 31) then pin 5 should be grounded? can pin 5 can also be grounded through the 560ohm resistance.
    plz sir reply quickly.thanks

    Reply
  27. AHMED

    I WAND TO KNOW THE PERFORMANCE PARAMETERS OF ADC ( CONVERSION TIME , RESOLUTION . MAXIMUM CONVERSION RANGE . COST PLEAS ANY ONE HELP ME TO THE ANSWER

    Reply
  28. seetharaman

    Kindly go through the following datasheet for 0 – 20VDC FS you have to use potential divider in the input.

    Reply
  29. Suvrodeep Ghosh

    I built quite a same circuit, except for r3=47k & c4=470nf. I also adjusted the potentiometer to read 100mV between pin 35 & 36. I was told that these are the ext. component values for 200mv full scale. i want to operate it on a 0-20V scale. The thing is displaying erroneous values. Please help!!!

    Reply
  30. adnan

    i connected the pin no 1 to 5v supply but it just brights the segment display but not effect on reading and when i vary the potentiometer it doesn’t effect on reading its remain unchanged
    plz tell me what can i do?

    Reply
  31. adnan

    its not working properly mr seetha raman its shows 26volts when i connect 3.7volts mobile battery and shows varying values can not calibrate plz reply

    Reply
  32. adnan

    i made this circuit but its not working properly showing anonymous values and when i rotate potentiometer its not effect on reading and its varies time by time what will i do

    Reply
  33. seetharaman

    Hi Adnan If your final drive devices have open NPN collector then you require common anode display such that the required segment can be pulled to ground for glowing.
    In case if your final drive device can give high output with suffucient drive current, then you require a common cathode disply such that when ever the disply input goes high that particular segment will glow.

    Reply
  34. RaYnoR

    Hello. i used very familliar schematic but when i conect to +5v and -5v (Power source) i get oly eights. why? i tried everything!

    Reply

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