I have an external UART module powered by a lithium battery that consumes about 100mA (max), I want to be able to power off this module through a GPIO on an ESP32.
Should I do it with a transistor? If so, NPN or PNP? How do I avoid phantom powering the module through its RX & TX pins?
Is this schematic correct?
Use optical isolators on them both.
No.
Put a part number on the FET but as drawn it will not work.
No, because a transistor will always have a 0.7V collector / emitter voltage drop across it.
The UART needs to be switched high side with a P channel MOSFET but you can't put 4.2V on a 3.3V output pin. You would need a second NPN transistor to switch the P channel.
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I don't have a part number, I've drawn this on MSPaint just to ask here if this is the correct way to power on/off an external module.
I'm still very confused on how to achieve this, should I switch the high-side/VCC? Should I switch the low-side/GND? NPN/PNP/MOSFET?
As drawn nothing will work.
The problem with using a PNP or a P-channel Mosfet in order to turn it off the gate, or base, has to be higher than the supply. As you only have a 3V3 powered "Arduino" (not actually a real Arduino) you can never turn it off. So you either need an extra transistor or FET.
The answer was given you in post #3
And you have been told that it is not correct and if you wire like it is shown you will damage your processor.
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