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I know if you reverse + and - on a voltage supply you can measure a negative voltage using a multimeter, but for an op amp they only have one negative pin so I don’t think reversing + and - would work because you would be connecting the - voltage terminal to ground, I’m a little bit confused about how to achieve this, could you please explain how to get a - supply rail Thanks, Be

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  • \$\begingroup\$ Choose Ground to be the V+ of an isolated converter to get V- out. Wherever you define 0V is "a local gnd". \$\endgroup\$ – Tony Stewart Sunnyskyguy EE75 Nov 24 '17 at 5:23
  • \$\begingroup\$ you are incorrect with your statement about the multimeter. you measure a negative voltage when the multimeter positive probe is connected to a voltage that is more negative than the mutimeter negative probe. it is when you reverse the multimeter probes. ... the power supply voltages do not reverse. \$\endgroup\$ – jsotola Dec 18 '17 at 5:09
  • \$\begingroup\$ Do you even need a negative supply? Many op-amps will work from a single supply depending on what you are trying to do. \$\endgroup\$ – Finbarr Dec 19 '17 at 11:47
  • \$\begingroup\$ A negative supply needn't differ from a positive one. It is just connected with its positive terminal to ground. \$\endgroup\$ – Whit3rd Dec 19 '17 at 11:56
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Use a DC-DC converter, a charge pump capacitive inverter or an inverting buck converter. Some type of switching supply is the easiest approach if you only have a positive rail available and actually require a negative rail.

There are easily available DC-DC converters that will accept a single DC voltage input and produce (say) +/-15V rails that are galvanically isolated from the input.

It's easier for your meter because it has an inherently isolated supply in the form of the battery.

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If you are going oldschool you have to have two transformers or one with 3 output leads of which one is in the smack middle of secondary winding. Usually op amps require +/- 15 V DC. Now all you need is 7815 and 7915 ICs.

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  • \$\begingroup\$ Hi koktelic, please include a reference/attribution for external content. I surmise it could be this one? \$\endgroup\$ – bummi Nov 24 '17 at 8:01
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    \$\begingroup\$ "Usually op amps require +/- 15 V DC" in days long gone by maybe, certainly not true any more. \$\endgroup\$ – Finbarr Dec 19 '17 at 11:45
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You may find this thread helpful.

Negative voltage from Arduino?

I would suggest you to do it with two batteries as shown below. However, your question lacks detail, so I can't recommend what would be the best possible solution for you.

schematic

simulate this circuit – Schematic created using CircuitLab

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    \$\begingroup\$ A bit of diligence here would have been desirable. The TL081 will not work with a +-1V supply. Also, this is probably the most cumbersome possible solution. \$\endgroup\$ – Marcus Müller Dec 19 '17 at 10:44
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    \$\begingroup\$ Removed the 1V altogether. If by cumbersome you mean hard to implement I respectfully disagree. \$\endgroup\$ – user94729 Dec 19 '17 at 11:38
  • \$\begingroup\$ By cumbersome I mean merriam-webster.com/dictionary/cumbersome "because of heaviness and bulk" \$\endgroup\$ – Marcus Müller Dec 19 '17 at 11:44

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