How to display ratio of 2 voltages?

Discussion in 'The Projects Forum' started by gpxfiles77, Nov 4, 2010.

1. gpxfiles77 Thread Starter New Member

Nov 4, 2010
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Hi,
New here, I do very basic electronis as a hobby.

I would like to have a cheap 3 digit LED display the ratio of 2 voltages in real time or just updated often. In other words if I have V1 and V2, I would like it to display the result of V2/V1. If V2 = 3 volts DC and V1=2 volts DC then the display would show 1.5

I have taken core electrical engineering courses as a student, but its not my field. I think this can be done by having the 2 voltages go to an IC (integrated circuit) and then somehow connecting the IC to an LED display?

Any ideas how this is done? Any help appreciated.

Mar 6, 2009
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3. gpxfiles77 Thread Starter New Member

Nov 4, 2010
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Thx for responding so quickly. I am not sure what that was but I think it actually creates an output voltage that is multiple of the input voltges and I can see how it could be used to divide to.

I dont need to have an output voltage created though. I just need to divide the numberical value of one voltage by another voltage and have whatever the result is displayed. I suppose it could be that the only way to do that is to create a voltage with the voltage multiplier then send that voltage to a voltmeter and display the results. Is this what you were thinking? Thx

4. gpxfiles77 Thread Starter New Member

Nov 4, 2010
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test - trying to set the email notification

5. eblc1388 AAC Fanatic!

Nov 28, 2008
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Yes. The IC is the ICL7106 3-1/2 digits A/D converter chip, arranged to perform ratio-metric measurement.

Use one voltage as Vref and the remaining voltage as measurement input to the IC.

The digital output on the IC be the ratio of the two voltages. e.g. 1300 = 1.3 times.

6. thatoneguy AAC Fanatic!

Feb 19, 2009
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What will be used for the display/output?

Microcontrollers often have multiple 10 bit ADC ports, math ability, and fairly easy to write to a LCD display. (PIC or AVR)

The only requirement would be voltages in the 0-5V range.

7. Kermit2 AAC Fanatic!

Feb 5, 2010
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Yes you DO need an output voltage. Your circuit must have a voltage to sample in order to 'know' what number to display.

Now, Wouldn't a simple high resistance value 3 part divider work for this? difference voltages put in at either end and a JFET opamp to sample the voltage across the center resistor of the network?

Still need to convert that signal to a digital value and send to display circuit, but the actual difference voltage in an analog form should be easy to achieve with just the voltage divider network.

8. Ron H AAC Fanatic!

Apr 14, 2005
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He doesn't need an output voltage if he uses a ratiometric A/D where, as L.Chung indicated, one of the voltages is the reference voltage, and the other is the voltage input of the A/D.
Ratio=Vin/Vref

A simple resistor divider cannot yield voltage ratios.

9. gpxfiles77 Thread Starter New Member

Nov 4, 2010
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Great information. I already like this site. Using the ICL7106 3-1/2 makes the most sense to me. Its cheap, I think I can hook it up and it looks like it already has the LCD on it. I initially read about the voltage divider and agree it does not appear to be able to create a voltage ratio. Its odd but I initially thought that this could be done using a simple circuit and using ohms law.