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.)