Re: BeagleBone Black and GPIO issues

[Lloyd Parkes <lloyd%must-have-coffee.gen.nz@localhost>]

On Mon, 2024-10-28 at 19:13 -0400, Mouse wrote:
> > When I enable a pullup the voltage on the pin reads 3.2 V on my
> > multimeter.  When I enable a pulldown the the voltage on the pin
> > reads 1.6 V which doesn't make me super happy, but it doesn't seem
> > to
> > be floating.
> 
> Did you try strapping it to Vcc and GND with some 3-10 K of
> resistance
> to see if that affects the voltage?

That's an idea.

OK, with a 6.7 kohm resistor connecting the GPIO pin to 3.3 V, I got a
0.54 V drop across the resistor and a 2.91 V drop from the pin to
ground. This is what I expect after inferring a 30 kohm pulldown from
the datasheet. 

Also, I set my multimeter to ammeter mode and put it inline between the
GPIO pin and 3.3 V and it read the nominal leakage current of 0.11 ųA.

>   Depending on various factors, 1.6V
> could very well be what you get for a floating input pin.  

The floating voltage appeared to be about 3.1 V, so I don't think it's
actually floating, but something is going on that I don't understand.

> And IMO if
> you take an input pin, enable pulldown, disable pullup, and don't
> drive
> the pin externally, it should measure pretty darn close to 0V.

I know right? 

I never studied electrical engineering. Maybe it shows. 

Ngā mihi,
Lloyd