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Scenario: The Uno is being powered by USB for programming, and the HC-12 wireless communications module is wired correctly. But it will not work.

In reading through the web literature, it is mentioned that to use the HC-12 in the high-power (100 mW) mode requires a power supply in excess of what the laptop's USB port will provide.

I am finding nothing on Stackexchange that addresses this issue.

So the question is, how do I get the power to run the Uno with the HC-12? I need to be able to periodically update the programming and test it while that auxiliary power is applied, and need to know it is safe to do so.

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There two options I have found that work well.

First is a simple wall-wart that provides 12 Volts to a barrel connector, like for a CCTV camera.

Or, if I want to run the Uno from a separate higher-amperage USB charging port I have found that there are "USB A Male to CCTV male" cables that work.

Doing the latter means the Uno is running at 5V instead of utilizing the on-board regulator to drop a higher-voltage input, which only matters if your circuit expects to find more than 5 Volts on the Vin pin (although that is not supposed to be an output pin, of course).

Through thorough experimentation I've proven that both methods work.

The best part is that the Uno can easily tolerate having both CCTV-style power and also being plugged into the laptop for programming and testing (like using the serial monitor).

Lesson learned: The HC-12 simply will not work without auxiliary power, and it is safe to provide such power while also plugging the serial port into a laptop.

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