On Tue, 12 Jun 2018 12:17:09 +0200, Mark J
 declaimed the following:

>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...

 Both leads are /seeing/ 5V; but the VM should not be sourcing any
voltage. A low impedance meter could load down the circuit (drawing power
from it, giving faulty readings if the source is limited in current).

 If the meter is seeing a 0V differential between 5V source and GPIO,
something else connected to the GPIO must be providing it (I've presumed
the camera module has been connected during these tests, and since it is
also powered from the 5V my concern is that the module output(s) swing
between 0V and 5V).


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 Wulfraed                 Dennis Lee Bieber         AF6VN
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