piclist 2001\04\26\115042a >
Thread: Pin impedance
face BY : David VanHorn email (remove spam text)

>First, are you charging and discharging through
>separate pins? They may have different properties.

I am charging through the same pin, discharging through different pins, and
measuring with two of three pins.
In the AVR, I could measure through the same pin I'm discharging with, and
then I could do all the measuring on one pin.

>The PIC output low (current sink) saturation
>voltage varies with current. By varying resistances
>there is a variance in current and also discharge
>curves. The output sat curves are in the datasheet.

Apparently this is what's giving me trouble.

>Maybe try using a second series resistor
>so your variable range is only 20% of the total,
>not 95% of the total. This should flatten it out
>a bit, also maybe try using higher value resistors
>to get the currents lower.

Thought about it, but it does make sensing the difference more challenging.

Dave's Engineering Page: http://www.dvanhorn.org
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