Return value of read_gpio_pin_analogue_value is unclear

[kierdavis]

It is not clearly documented what the scale of the return value of GPIOPinInterface.read_gpio_pin_analogue_value should be. Is it

• between 0 and 1?
• between 0 and the maximum ADC reading? (usually 255 or 1023 for an arduino)
• between 0 and the reference voltage? (usually 5 V for an arduino)

I think the last option is the most useful to the user.

https://github.com/j5api/j5/blob/master/j5/components/gpio_pin.py#L76

[trickeydan]

The latter was my intention when I wrote the interface.

[trickeydan]

We should clarifiy this in code, but between 0 and the reference voltage? (usually 5 V for an arduino) is what it should be

[kierdavis]

Makes sense to me.

I think (not sure since it's been a while since I looked at this) that there's a few places in the code that don't follow this, so we should look through and make sure the right scale is being used consistently throughout the codebase.