Dont need a super accurate, super high bandwidth In Amp...

[treez]

Hi,
We wish to compare two voltages and see which is highest, and get a rough measurement of the difference. We came up with the attached circuit.
Its cheaper than an In Amp….eg we could just use an MCP6002 dual opamp. Though we aren’t sure. We can’t find In Amps with this ease of functionality. Do you know of one off hand?

LTspice sim and pdf schem attached

 

[betwixt]

Can't you just scale the two voltages and feed them differentially to the two amps inputs, one with low gain (or unity) to give the difference and the other with high gain so it works like a comparator to indicate which is the higher.

Brian.

 

[KlausST]

Hi,

Basically it should work.
What's wrong with this circuit?

It maybe should work with one OPAMP only...and a bit less resistors.

Klaus

 

[Easy peasy]

Brian's idea will work but need needs a split supply for the op-amp - unless you offset each input from the ( accurate ) 5V supply ...

 

[BradtheRad]

A simple differential detector is a Wheatstone bridge.



Anti-parallel led's act as visual indicators.
In some cases you don't need the ground connection.

Or, feed the left and right nodes to the inputs of an op amp. Adjust resistor values as needed.

 

[Easy peasy]

LM324 / 358 ( same IC but pair / quad ) would be fine for this ...

 

[danadakk]

What is accuracy you are seeking for the measurement ?

Once you get measurement what do you want to do with it ?


Regards, Dana

- - - Updated - - -

You could use a dirtball cheap processor with ADC with differential front end.

Just an 8 pin part with a cap to bypass its supply rail. Anywhere from 8 to
20 bit accuracy, the latter in bigger packages. Some with precision Vref
onboard, some Vref is supply pin.

Note R divider still external and needed for both comparison supplies.

It all depends on what the overall function and accuracy of the design requirements are.


Regards, Dana.