On 12/06/2018 11:17, Mark J wrote:
> The use of even a high impedance voltmeter between 5v and 3.3v GPIO pins
> worries me - maybe this has already been covered, but...
>
> If that meter is registering 0v between 5v and a GPIO pin, then that
> implies /both/ leads are at 5v, so the 3.3v pin has 5v on it, all relative
> to 0v. Can the use of a voltmeter in this way kill an IO? My feeling is
> that a voltmeter should always be used from 0v to 5v or 3.3v, to avoid
> this issue. Maybe I'm wrong...

You should only ever measure between 0V and a GPIO pin, not any of the
power pins, and particularly not 5V.

---druck

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