When connecting an Arduino Micro to a 12V battery, spikes at a frequency of about 7.6kHz are observed on the supply voltage.
First is a negative spike of more than 1V. After about 6 usec, there is a positive spike of about the same magnitude, followed by a ring-down. There is about 40cm of 18 gauge wire between the Arduino and the battery. The battery is a fully charged 10Ah sealed lead acid battery.
Sometimes half the frequency is observed, sometimes double; seems to be dependent on the current draw on the 5V supply of the processor. For the test, only the Arduino was connected and its steady-state current draw is about 40mA. The 5V supply is relatively stable, however, a small (maybe 100mV) increase followed by a decrease is observed.
This is reproducible on my two recently purchased Micro boards.
It almost seems as if the supply voltage is momentarily shorted.
Has anybody else seen this? Any possible explanations?