On 22/01/18 15:50, Dennis Lee Bieber wrote:
> 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.
>
I have exported the GPIO17 pin and it does show up ok, but when I do
echo echo out > direction OUT or out, I get
-bash: echo: write error: Invalid argument.

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