In message 
          mm0fmf  wrote:

[snip]

>>>>
>>>>     Uhm... 0v between "motion pin" and 5v pin means the "motion pin"
>>>> is at
>>>> 5v also...
>>>>
>>>>     BUT! RPi GPIOs are 3.3V inputs...
>>>> http://www.mosaic-industries.com/embedded-systems/microcontroller-projects
>>>> /raspberry-pi/gpio-pin-electrical-specifications#rpi-gpio-input-voltage-an
>>>> d-output-current-limitations
>>>>
>>>>
>>>> A 5V signal on that "motion pin" could easily result in burning out
>>>> the RPi
>>>> GPIO (if you are lucky, only the one GPIO will be killed)
>>>> http://www.notenoughtech.com/raspberry-pi/rpi-gpio/
>>>>

[snip]

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...

--
Mark J
From RISCOS 5.23 on a BeagleBoard-xM and Raspberry Pi2B
- and Linux on a PandaBoard ES and Raspberry Pi3B

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