On Mon, 22 Jan 2018 11:49:33 +0000, RobH  declaimed the
following:

>
>I don't know what the difference between active low and active high wiring.
>

 I had provided the description... In short, active high presumes ground
is the "normal/off" state for a signal, and one sets the voltage to high to
turn it on. Active low presumes the "normal/off" state is high voltage, and
the signal is on when pulled to ground.


>
>I've just done some checking of some of the GPIO pins with a voltmeter,
>and got this:
>
>GPIO 17 0.06 vdc
>GPIO 27 0.01 vdc
>GPIO 22 0.07 vdc
>GPIO 23 0.05 vdc
>GPIO 24 0.02 vdc
>GPIO 08 3.25 vdc
>GPIO 07 3.25 vdc
>GPIO 25 0.01 vdc
>
>Now if GPIO is only measuring 0.06 Volts, that is not enough to power up
>the led. Should it be connected to a 3.25V pin instead.

 But what state were those GPIOs commanded to be in. 0.0x appears proper
for a GPIO commanded to a Low state, and 3.25 looks appropriate for those
commanded to be in a High state.

http://www.auctoris.co.uk/2012/07/19/gpio-with-sysfs-on-a-raspberry-pi/

That is: using the sysfs access (export those you were testing), set
DIRECTION to OUT, then set VALUE to 1... You should now measure around 3.3V
on the GPIOs (make sure to look at the correct pin mapping to the GPIOs).
Finally, set VALUE to 0 and measure -- they should now be near 0.0.
https://elinux.org/RPi_Low-level_peripherals#Interfacing_with_GPIO_pins
https://learn.sparkfun.com/tutorials/raspberry-gpio/python-rpigpio-api
(note that the RPi package supports use of the board/socket pin numbers, or
the chip set internal pin numbers -- if you are wiring using the board
numbers, but are in chip mode when commanding, you could be corrupting
something critical to operation)

 Note -- in that link they are using a transistor as an electronic gate
to avoid drawing much current from the GPIO itself.
--
 Wulfraed                 Dennis Lee Bieber         AF6VN
    wlfraed@ix.netcom.com    HTTP://wlfraed.home.netcom.com/

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