As the title says, simply, can I use the 3.3v and 5v power pins on the GPIO connector as the reference voltages for a level shifter, or do I need some other reference?
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Why does a level shifter need a reference voltage? You probably need to reference the device you are planning to use. – joan Jun 14 '20 at 21:34
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"Reference voltage"... do you mean supply voltage?
The answer to your question is: "Yes - you can probably use RPi's 3.3V & 5V supples to power your level shifter.".
The caveat was added because you didn't specify a particular device, and there are many devices called "level shifters".
Both the 3.3V and 5V regulators on the RPi have some "excess" capacity - by that I mean they are able to source more current than is typically used by the RPi, while maintaining specified voltage levels. See REF1 and REF2 for details. Typical "level shifters" such as this one from AdaFruit, and this one from Texas Instruments can be powered from the RPi regulated supplies.
If you want to minimize clutter and wiring, you may prefer a level shifter that operates from a single supply (e.g. 5V). The Texas Instruments part linked above is one example of a single-supply level shifter.
Seamus
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Thanks....that's the exact answer that I was looking for. I'd like to make a 'HAT" for my RPI parts with bi-directional level shifters just to protect the GPIO for accidental connection to 5VDC I/O, and will use the same parts as the AdaFruit modules, but not those modules, because they cost too much to put on the 10 RPI that I have. I'm probably being rediculously paranoid, but that's where I'd like to go. – crusader27529 Jun 15 '20 at 20:46
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@crusader27529: Glad it helped. [Please read this](https://raspberrypi.stackexchange.com/help/someone-answers) – Seamus Jun 16 '20 at 00:14
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The High and Low voltage pins of a level shifter should be connected to the respective supply voltages of the 2 devices it is intended to interface.
Milliways
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