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Thinking about supply voltages, and just voltages in general used to power anything, does, say a 5v supply alway have to come from +5V and ground, or can you bias it to any other set 5V apart, like 12V and 7V, or 2V and -3V?. Since voltage is just potential difference right?

Now I know they bias transistors for amplifiers, but could you do such a thing to a microcontroller? (No application just really curious).

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You most certainly can.

But, be sure to take care to shift all your datasheet values correctly. This especially includes absolute maximum ratings. Also have a look at the protection diodes often found around IC pins.

What makes this often very useless (or sometimes very useful) is that the logic levels are also shifted.

This is in particular done with operational amplifiers. There the manufacturer may even be nice enough to specify typical shifted supplies for you.

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  • \$\begingroup\$ Wow didn't know that, thanks. So offsetting the voltage supply would mean that all the digital ones and zeros would operate at that same voltage aswell? \$\endgroup\$
    – ezra_vdj
    Commented Oct 17, 2015 at 23:30
  • \$\begingroup\$ Yes. Often datasheets state that explicitly in a sentence like "All voltages referenced to GND pin". \$\endgroup\$
    – J A
    Commented Oct 17, 2015 at 23:31
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Yes! Microcontrollers don't care about the voltages at your battery - they only see the voltages at their power pins.

The biggest problem with doing this is that it's easy to go outside of the microcontroller's limits. A lot of chips will get damaged if any of the pins drop below -0.3 V relative to the ground pin. If your micro's ground is really at 7 V, then that means connecting any pin to a voltage lower than 6.7 V would damage it. Not great, but as long as you're careful, it's not a problem.

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