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I am looking to use a Raspberry Pi to power and read the current from a current-to-voltage converter. I am currently using two batteries to power the operational amplifier, as shown in the schematic below. Please ignore the potentiometer, it is an attempt at mimicking a sensor and is for illustrative purposes only. I would like to measure the current going through the sensor in just one direction.

Constant Voltage Schematic

However, I am finding that the 9V batteries I'm using to give the op-amp a negative voltage are running low pretty quickly, so I would like to power the op amp through the Raspberry Pi.

The sensor has a constant voltage input of 50 mV and a variation in output voltage from the op amp of 1 mV (even with the gain). The sensor is similar to a thermocouple or resistance temperature detector in terms of its small changes in current.

I am unsure if using a resistance divider or similar (as shown here: http://tangentsoft.net/elec/vgrounds.html) will wash out the signal. E.g. Voltage division with 2.5 V going into the op amp when I'm looking for mV changes.

Is there a way to redesign the circuit to operate from a single supply voltage source? Thanks!

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If the only reason is the battery then you can use the 5V rail for positive supply and a negative voltage generator like the one in this example: Build Your Own Negative Voltage Generator There are many examples on the internet.

Take care about the input and output voltage range which will be in this case +- 3V (for VCC = +- 5V)

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  • \$\begingroup\$ Is this similar to a charge pump? Is it possible to get a chip-based solution rather than building a negative voltage generator? docs-apac.rs-online.com/webdocs/0f73/0900766b80f73124.pdf \$\endgroup\$ – Jeremy G May 30 '18 at 7:14
  • \$\begingroup\$ @JeremyG Yes, a charge pump. The one in the link is also regulated which is good. \$\endgroup\$ – Dorian May 30 '18 at 7:25

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