So if the sensor is outputting 96 mV, after the signal conditioning circuit, it should give 0 V . And that 0 V linearly increases to 1 V (being 3.7 V max. sensor output).

We learned about the Wheatstone bridge and Anderson loop, but I don’t know how to apply those with voltage (rather than an RTD like the book details). I would be happy to read any relevant online sources for ideas. I just keep running into potentiometer like circuits.

Could the Wheatstone or Anderson constant current loop work with a variable voltage like this? I did create an Anderson loop (previous project) with a RTD, but I don’t know what to change for a different configuration:

(That’s an instrumentation amplifier.) I realize this circuit has nothing to do with the problem posed.
I'm pretty lost.
What about a voltage divider to get rid of that 96mV, first?
0 = 0.096*R2/(R1+R2)…or no?

 

If I understand you, you need an instrumentation amplifier to provide a small offset and a gain of about 1/4th. That’s a very standard opamp circuit, just google it.

A starting point: https://en.wikipedia.org/wiki/Instrumentation_amplifier

An ending point?
https://www.analog.com/media/en/tra.../designers-guide-instrument-amps-complete.pdf

 

hi Adam,
Please post a datasheet/link or part number for the sensor type that you plan to use.
E

 

At the most basic level you need a circuit that subtracts out offset
and gains up the signal. Think straight line plot where we want the
line that crosses the origin, not the line that is offset when sensor
output from circuit is supposed to be zero.

Thats a classic subtractor circuit that has G and can be fed an offsetting V.

The offset is common mode, contained in the signal of interest, so you need
to supply an external Vref to subtract out the CM signal.

This might help -

http://www.ti.com/lit/an/sloa030a/sloa030a.pdf


Regards, Dana.

 

maxbotix.com/documents/XL-MaxSonar-EZ_Datasheet.pdf

 

I can use any configuration with +/-5 V supplies. (I don't need to use an instrumentation amplifier.)
Last week I tried a simple inverting op-amp with unity gain amplifier:

But that doesn't work with 96mV obviously. Today I tried adding to that circuit:


I was told to connect the output of the second op-amp (which provides -5 volts) to the summing node of the first op-amp through a resistor that has a value selected to positively offset the first op-amp’s output (multi-turn precision trimmer of about 20 kΩ), resulting in the first op-amp's output spanning 0 to 1 V.

→ Where did I go wrong with their advice? (And ya...I should stop with the voltage divider nonsense.)

Thanks for any help.

 

hi Adam.
Using that second circuit, what is the output voltage when the Vsense is 3.7V.?
E

Which type of OPA's are you using.?

 

For the simulation, I'm just using 741s. Here is the min and max for the last circuit:



So 0.036 and 0.39 V.

 

hi,
This is your circuit in LTSpice, looks a very close solution.?
E

 

hi,
This is your circuit in LTSpice, looks a very close solution?
E
View attachment 170885

I mean, it's still 26mV off at the minimum (input 96mV).

 

hi,
Consider this simpler option. Using MCP6001 OPA
E

 

hi,
Consider this simpler option. Using MCP6001 OPA
E
View attachment 170888

Very cool. So the MCP6002 is the through hole and the linear op-amp is the way to go:
INA126 is $3.15 (instrumentation amp), while the MCP600 is only $0.34

 

I don't need to use an instrumentation amplifier.

You're trying to adjust zero and span, or offset and gain. By definition, you are making an instrumentation amplifier.