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I am using a pair of strain gauges to make a weight scale. The strain gauges are the three-wire type that you can by on Amazon or Sparkfun. The strain gauges form a full wheatstone bridge, whose differential output voltage varies from -6mV to around 10mV. I'd like to amplify this signal and then sample with an ADC. But my board does not have a negative voltage supply.

How can I shift the differential voltage so that it starts out non-negative, and remains positive for the rest of its swing. In other words, make the differential output from the wheatstone bridge go from 0mV to 16mV?

For reference, this is the circuit I am using, from the INA332 datasheet.

Reference schematic

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Your output voltage is relative to the Vref pin.

If you fed the amplifier, ADC and strain gauge all from 0v and 5v, then taking Vref to mid rail would give you an output about mid rail, nicely in the 0 to 5v range of your ADC.

That amplifier only gives you 5x gain in its default configuration, that's not a lot to follow a 16mV swing. Use the Rg terminal with a pair of reistors as shown in the data sheet to increase the gain.

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  • \$\begingroup\$ This is correct. Can use Vref to park the output right where I need it. And with external resistors, 100x gain should suffice. Thanks! \$\endgroup\$
    – ADB
    Commented Feb 12, 2017 at 10:06

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