Choosing right OpAmp


I bought piezoresistive pressure sensor. Excitation + and - is 10Vdc 1.5mA constant. Output + and - is min 40mV and max 150mV.

I want the output to be close to 0.1Vdc to 3.3Vdc. What OpAmp to look for, and how to calculate the right resistors for it. Thanks

For a wheatstone bridge output (two pins) you need a instrumentation amplifier.
Some Arduino boards or external ADC's have a differential mode with a gain. That is the same as the instrumentation amplifier.

Sometimes it is possible to connect them directly to a Arduino board to get a rough indication of the pressure. Then you know if it is working.

Can you tell which pressure sensor it is ?
What is your project ? We like to have a broader view.
Which Arduino board do you use ? If you use a ESP8266 or ESP32, then it will not be accurate.

There are pressure sensors that output 0.5 to 4.5V, they go well with a 5V Arduino board. Those are also available in 3.3V versions.

What is your experience with op-amps?

You might find this useful Using Operational Amplifiers in your Arduino project

I have Arduino Due and ESP32. Its pressure sensor, negative and positive, -1bar to 4bar, two inputs, two outputs. I am measuring fluid positive pressure and negative pressure, when there is no fluid.

I have zero experience with op-amp.

Thanks, I will read that.

Does the sensor have a brand and a number ? Can you show a photo of it or give a link to it ?


That sensor will probably work with 5V as well. I think it will work also with 3.3V and probably with a lower voltage. For example the 2.5V from a INA125.
So that sensor with a INA125 instrumentation amplifier should work.

I think there is only a wheatstone bridge inside that sensor.

The challenge with many single-power-rail op-amps is that they cannot drive the output that close to the power rails. Especially towards the GND line.
Usually, if you can get to 0.7 v of the rail you are lucky.
However, you can buy "rail-to-rail" Op-Amps which can get very close to the power rail levels.
So, they key thing to look for in this case is how close the op-amp output will drive to 0V.

Now.... if you use an Op Amp with both + and - power rails (like +-12V) that is s better way to do. In this case any standard op-amp should do. Even the humble 741.

If you do that you need to remember to protect the microcontroller from being fried by the opamp output - 10k resistor to limit current for instance.

These days there are plenty of rail-to-rail 5V capable opamps out there for interfacing to microcontrollers, Microchip have a large range I believe, checkout
for instance the MCP6002.

But all this is immaterial because you have a strain-gauge sensor which immediately
suggests using an instrumentation amp, and the HX711 is pretty-much the "go to"
device for this in the Arduino world, lots of examples out there to copy.

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So if I use HX711, use 3.3V as input voltage, the sensor will work?

The HX711 module might have problems with 3.3V:

The sensor can be powered (excitation) with max 10volt, but that doesn't mean it won't work with a lower voltage. HX711 boards have a ~4.3volt excitation voltage, which is perfectly fine.

4.3volt excitation means that you must power the HX711 board with 5volt.
But... if you use a 3.3volt processor, you can only use a HX711 board with two supply connections.
A 5volt supply for the sensor part of the HX711 (VCC), and 3.3volt supply for the logic part of the HX711 (VDD). Only Sparkfun sells boards like that. Or modify a common board yourself if you can.

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