The post explains a very simple digital panel type voltmeter circuit using a single IC L7107 and a few other ordinary components. The circuit is able to measure voltages right up to 2000 AC/DC V.
About the IC L7107
Making this simple digital panel voltmeter circuit is particularly easy due to the availability of the A/D voltage processor chip in the form of IC L7107.
Thanks to Intersil for providing us with this wonderful little IC L7107 which can be easily configured into a wide range digital voltmeter circuit using a few number of common anode seven segment displays.
The IC 7107 is a versatile, low consumption 3 and 1/2 digit A/D converter IC which has in-built processors such as seven segment decoders, driver for displays, set reference levels and clock generators.
The IC not only works with ordinary CA seven segment displays but also with liquid crystal displays (LCDs) and has an in-built multiplexed back plane illuminator for the connected LCD module.
It ensures auto zero correction for inputs less than 10uV, a zero drift for inputs below 1uV/oC, bias current for inputs of maximum 10pA and cross over error of less than a single count.
The IC can be set with ranges as high as 2000 V AC/DC, and as low as 2mV, the later makes the IC very suitable for measuring low inputs from sensors like load cells, piezo transducers, strain gauges and similar bridged transducer networks.
In other words, the chip may be simply configured for making products like digital weighing scale, pressure meters, electronic strain gauge, vibration detector, shock alarms and many similar circuits.
Needless to say, the IC L7107 can be also rigged into a simple yet accurate panel digital voltmeter circuit, which is what we are presently interested in.
Simulation and Working
Referring to the circuit diagram below, the unit is a full fledged digital voltmeter circuit which can be used for measuring direct voltages right from zero to 199 volts.
The range can be appropriately widened or shortened simply by altering the value of the 1M resistor positioned in series with the input terminal. With 1M, the range gives a full scale of 199.99V, with 100K in place the range would become 19.99V full scale.
The circuit requires a dual +/-5V supply for operating, here the +5V may be strictly acquired from a standard 7805 IC regulator circuit, the -5V is automatically created by the IC 7660, and fed to pin#26 of the IC L7106.
The three 1N4148 diodes connected in series with the display supply line ensures optimal operating voltage to the displays for illuminating them with correct intensity, however for brighter illumination, the number of diodes may be experimented, as per personal preferences.
The 10K preset across pin#35/36 is used for calibrating the voltmeter correctly and must be set such that exactly 1V appears across pin#35/36. This will set up the circuit for displaying the measured magnitudes accurately as per the given specs, and datasheet of the IC.
Pinout details of IC L7106 for interfacing with a 3 and 1/2 digital LCD display.
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Alwin says
hello sir
I wanna measure 0.001v – 5v, which ic is good for this (analog to digital converter ), Is this possible to measure this voltage range
Swagatam says
hello alwin, digital will be obviously better….yes it is possible to measure this range with any good quality DMM
dada neamul says
sir
You Use Two 7 Segment display. If I Want To Use One 7
Segment Display ..! What Should I do…… Sir I using A Variable DC Power Supply Unit But I Have No ckt Diagram for Digital Volt Display.
Swagatam says
Dada, I don't think a single display would be possible with this IC, because the IC is specifically designed to drive a 3.5 digit display
dada neamul says
thanks for your compliment.
Shreyansh Likhar says
can i interface it with any microcontroller(8051 or AVR)?
Swagatam says
yes, you can do it…
Nitin Sarda says
Sir,
I have a digital voltmeter which measure the 24 volt dc.
When it was new then voltage was measuring ok. But after 2 months, voltage reading fluacting in display. I mean it show 25,32,47 volt etc.
How to stop the wrongly fluction on display??
Swagatam says
Nitin, if it has a selector switch then the problem could be in the switch, just move it rapidly up/down and then check the response….loose prod connectors could also be an issue, so you can check it as well.
if these are OK, then your meter is surely malfunctioning.
Bradley Nelson says
Sorry if this comment posted more than once. I've had a hard time submitting it.
I'm wondering if this circuit could output the voltage reading to an Arduino instead of the LEDs? I'd like an Arduino to be able to read voltage and store the value as a variable in a program.
Will this meet that need?
Swagatam says
I am sorry I have no idea how this circuit may be configured with an Arduino…
Bhaskar Srivastava says
Can this Circuit can be used to measure AC house hold Supply. ??
Swagatam says
yes, after appropriately rectifying and calculating the input resistors
frank rebosura says
Sir it is directly connected to the AC output voltage of the generator set to measure its output voltage or it is only used to measure DC voltage?
Swagatam says
convert AC to DC and then the 10K preset across pin#35/36 could be used for calibrating the voltmeter correctly and must be set such that exactly 1V appears across pin#35/36. This will set up the circuit for displaying the fed magnitudes accurately.
style says
Thanks for reply sir. Why its called 3 and half digital display ..
style says
Hello Sir
Thanks for reply. can u tell me the address in mumbai.
regards
Swagatam says
you can many good shops in lamington road (grant road)
sinu sivadas says
Hello Sir
Is this IC is available in India particularly in Bangalore and what is its cost
Regards
Swagatam says
Hello sinu, it's available in Mumbai, I am not sure about other states or Bangalore
vishwas poojary k says
what is the indian price of that ic?
Swagatam says
no idea, sorry
currentviews says
Sir,
Its really excellent Project Post. i liked it too much, already i bought every parts . here i did not get ICL7106. but i got ICL7107 they told me its similiar like ICL7106 , i need to know how can i connected it with 7 segment display, is it like ur instruction numbering, basically i considering number 1 pin from left side and continuously from right. like IC pinout perhaps its not right way about pin connect among IC and 7 segment display. please i need to know about 7segment display pin setup configuration ..
Swagatam says
thanks currentviews,
the best place to get the information is to look in its datasheet.
Please type "datasheet" with the "part number" or simply "7-segment display datasheet" in Google search…… you will get a comprehensive info regarding the same.
Tanmay Deshmukh says
And sir where should the preset to be connected?
Swagatam says
Hello Tanmay,
pin36 is connected to the slider arm of the preset.
The preset has three pins, the center pin will go to pin36 and the other two pins will connect with pin35 and the 15k resistor…..
Tanmay Deshmukh says
Hello sir,
As am a very beginner, confusion is How is the pin 36 of ic 7106 connected, i think is in between two resistors given.is it ?
Saroj Panda says
it showing only a point in the second display nothing else
Swagatam says
did your apply any input voltage?
farkhana says
Hi there,
I have made using same IC. However, my input is 4-20mA and the output is indicator that shows -30 to120.
Is it possible to show -30 on 7-segment?
Do you have any idea how to do that?
Many thanks for your help.
Swagatam says
Hi, There should be a way definitely, however I have no idea how to do it.
Abu-Hafss says
Hi Swagatam
Is it possible to convert/modify a digital AC voltmeter to use as a DC voltmeter?
AC voltmeters are cheap and easily available in various sizes.
Swagatam says
Hi Abu-Hafss,
I am not sure how to make an RMS detector, without this it would be impossible to convert AC meter into DC.
Subhramanyam says
I am expecting your reply soon sir!!!!!!
Subhramanyam says
It is ok sir. But i have a small doubt.
Eventhough i am caliberating this circuit with a known frequency signal, will it be same for another signal having a different frequency but having the same peak to peak voltage of the known one since it is not functioning as a frequency to voltage converter, otherwords saying the circuit functions only as a voltage finder. If anything wrong i have said, please correct me Sir
And also tell me is it possible to adjust the reading to 50 when 50 Hz is fed ( i think only the voltage equivallent will be shown)
Swagatam says
Subhramanyam , the above circuit is a voltmeter not a frequency meter, so you cannot feed frequency directly to this circuit, as mentioned in the above comment and as per your previous comment under the "simple frequency meter" article, you will have to integrate the frequency meter circuit output with the as above circuit to get a digital reading….I think this is what you had asked in your first comment, right?
Swagatam says
..the frequency meter circuit using IC 555 can read right from 10Hz to 10kHz comfortably, so 50Hz won't be an issue.
Subhramanyam says
How can i use this circuit to measure frequenc SIR?
Directly feding the input signal into the voltage measuring terminals'???
I have 4 no.s of 7 segment single LCD displays ( each having 10 legs ) with me. Can they be used? How to wire them?
Swagatam says
yes connect the frequency meter output to the shown points and adjust the 10k preset for calibrating it with the known frequency value.
You will have refer to the datasheet of the displays online and identify the pinouts and then integrate with the above circuit.
Abu-Hafss says
Hi Swagatam
I am bit confused for the connections of ICL7106 to a 3.5-digit LCD (H1331C).
a) Where to connect pin 19 (AB4) of the IC?
b) Where to connect pin 20 (POL) of the IC?
c) Where to connect pin 21 (BP) of the IC?
d) What is pin 8 (DP3) of the LCD for and where to connect?
e) What is pin 12 (DP2) of the LCD for and where to connect?
f) What is pin 16 (DP3) of the LCD for and where to connect?
g) Where to connect pin 1 (COM) and pin 40 (COM1) of the LCD?
Anonymous says
Hi sir,
For me two digits is enough. What changes should it required?
Thanks
Naresh
Swagatam says
You can refer to the datasheet of the IC and check if this option is enabled in it.
Anonymous says
when i discnct source voltage of ic and again energize ic i hv to calbirate voltage reading again by using pot . . . wher is da prob?
Swagatam says
don't use a pot, instead use a preset, it's more firm and will keep the setting intact, if possible glue it after the setting is done.
sharojalhasan says
PLZ HELP ME I WANT A remote cöntrol relay circuit
pp says
Hi,
Can it be constantly kept attached to AC mains..is it suitable???
Swagatam says
Yes, but through an AC/DC adapter.
Sayad Hadia says
Valuable for all specially Engineering students
Swagatam says
thank you!
Anonymous says
hello Sir,
kindly post 7x1W high power LED SMPS driver circuit