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 and R4=0 gives 0-2V 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.
Hello. i used very familliar schematic but when i conect to +5v and -5v (Power source) i get oly eights. why? i tried everything!
would you please send me the schematic used.
well dude what is the range of it….
can the circuit be used as a pressure sensor?
what is the difference between common anode and common cathode 7 segment display
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.
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
when i connect 3.7volts battery to the input its shows 26 volts what will i do plz help me?
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
Hi Adnan hope you are supplying both +5, common and -5 volt to pin no1,21 and 26 respectively. in the above circuit pin no 1 is to be connected to +5volt. Thanks for pointing the mistake.
refer to the data sheet enclosed
http://www.intersil.com/data/fn/fn3082.pdf
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?
plz help me
ans me mr seetha raman what will i do
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!!!
Kindly go through the following datasheet for 0 – 20VDC FS you have to use potential divider in the input.
Kindly go through Intersil datasheet which is more informative
http://www.intersil.com/data/fn/fn3082.pdf
I WAND TO KNOW THE PERFORMANCE PARAMETERS OF ADC ( CONVERSION TIME , RESOLUTION . MAXIMUM CONVERSION RANGE . COST PLEAS ANY ONE HELP ME TO THE ANSWER
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
Hi Zernab go through the following site for full details
http://www.intersil.com/data/fn/fn3082.pdf
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.