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AStar32u4 USB + VIN?

I’m using an Astar32u4 micro powered via the USB connection.

Is it ok to add a 15v source to VIN and have both USB and 15v VIN source present at the same time?

Hello, kenr.

I moved your post to the “A-Star and Orangutan” section of the forum since it is primarily about the A-Star 32U4 Micro.

The A-Star 32U4 Micro features a power selection circuit that allows both USB and VIN to be connected at the same time; when this is done, the A-Star will draw power from VIN. You can find more information about this in the “A-Star 32U4 Micro pinout and components” section of the A-Star 32U4 user’s guide.

However, 15V is the maximum recommended operating voltage for that board, so you should be careful if you are using a 15V supply since you will not have much margin of safety.


Hi Brandon,

Thanks for the advice. The 15v is from a 7815 regulator.

Would it be protection enough to use two 1n4001 diodes in series to drop the voltage?


Hello, Ken.

In general, if your 15V supply is steady (such as from a regulator), it should be okay. However, if you are powering devices that could be particularly noisy, such as motors, you might want to take some precautions like adding capacitance to the supply line.

You could also consider adding a separate regulator to power the A-Star from an intermediate voltage. Alternatively, you could switch to the SV version of the A-Star 32U4 Mini, which has a wider operating voltage of 5-40V:

  • Brandon

I added a single series 1N4001 in the 15v line from the regulator. The voltage at VIN is 13.6 and everything looks good.

Thanks to Brandon for his prompt replies.


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