Leonardo and micro: high pitch noise when powered from Vin I have an issue with several Leonardo and Micro boards.

On all of my boards, there is a sawtooth of about 690mV ptp @ 4kHz on the 5V supply when powered from Vin (external power).
The frequency changes slightly when changing input voltage from 7V to 12V.

C12 is a capacitor on the Leonardo board that is making the acoustic noise, it is "singing" with the frequency of this sawtooth. It follows the voltage regulator NCP1117 for the 5V power supply generation.

According to the schematics of the Leonardo and micro, the voltage regulator used on these boards should be the NCP1117, but on the boards I have, there is no number printed on this component, so I suspect an alternative was used, with these annoying results...

For a project I have for generating audio signals, this noise was unacceptable, so I cut out the regulator and powered everything with an external LM7805. One should not power the module via USB then as long as the external power is connected!!!

Anyone having the same trouble with these boards?
Other solutions?

(The Leonardo is a genuine Arduino board.)
Yes, I've had this problem on a number of boards. It seems there are some faulty units coming out of the factory. I've had them replaced by my supplier, but I end up being sent more faulty boards.

It makes any kind of accurate ADC reading impossible.

A quick way to work out if your board has this problem


Place a jumper between 3.3v and A0 
Put an analogRead in a loop and println the result
When powered by 5V you'll see a fairly constant value (around 670), varying by 1 or 2
When powered by 12V, if you have a faulty board, you'll see varying values, deviating by 50 or more.


There's a couple of solutions/workarounds to the problem listed here: http://forum.arduino.cc/index.php?topic=235729.0.