Digistump Forums

The Digispark => Digispark (Original) Support => Topic started by: simonriskjaer on December 19, 2016, 01:22:38 pm

Title: Analog read with internal pull-up on pin 3
Post by: simonriskjaer on December 19, 2016, 01:22:38 pm

Hi,

I am trying to use pin 3 as an analog input. However, it seems the internal pullup is enabled when the port is in input mode. And so i keep having around 3V on it, rendering the ADC useless.

How do i disable the pullup?

Title: Re: Analog read with internal pull-up on pin 3
Post by: exeng on December 19, 2016, 03:52:38 pm

Why not use another analog pin (keep in mind the analog to physical pin mapping)? P3 is the only one with a default pull up.

http://digistump.com/wiki/digispark/tutorials/basics

Title: Re: Analog read with internal pull-up on pin 3
Post by: simonriskjaer on December 19, 2016, 11:57:22 pm

All other pins are in use for this project. I need P3 as an analog input.

There must be some way of using it as an analog input, i'm just not seeing it :-)

Title: Re: Analog read with internal pull-up on pin 3
Post by: exeng on December 20, 2016, 12:40:43 am

Looking at the schematic I see 2 possibilities, neither of which is ideal or perhaps feasible.

1. A cut and add on the board/schematic that switches out the external pull up for ADC input. (Not very practical)
2. Pull down the pin to ground effectively  creating an external voltage divider which would lower the input with nothing attached. (Would have to experiment with this to see if feasable)

Unless I'm missing something obvious these are my first thoughts.

Are you sure you can't rearrange  the pin usage to avoid P3 for ADC?