[PD] problem with arduino digital ins - Pduino-0.5beta8 / Firmata 2.1

[Martin Peach]

Roman Haefeli wrote:
> On Wed, 2010-06-30 at 14:12 +0200, Ingo Scherzinger wrote:
>> Hi Roman,
>>
>> this solution is working also. So in this case it's not really necessary to
>> change the firmata itself. Anyway, I would prefer to have this behaviour as
>> the default behaviour, i.e. included in firmata. At least all of this this
>> should be documented.
> 
> Actually, it is here: 
> http://www.arduino.cc/en/Tutorial/DigitalPins
> 
> It's not firmata exposing this functionality, but the arduino. So I

And shining through that is the actual microcontroller. It's useful to 
read the data sheet to see what is possible:
http://www.atmel.com/dyn/resources/prod_documents/doc8271.pdf

> think it's correct that Firmata handles it transparently, so that from
> Pd you are still able to decide yourself, whether you actually want that
> pull-up resistor or not. 
> 
> Enabling it per default is _not_ a good idea, since there are many
> applications, where you deliberately want the pull-up resistor not to be
> enabled. Imagine a sensor with a very high impedance (for instance, an
> LDR in series with a fixed 1 MOhm resistor), with the pull-up resistor
> activated the input would always be HIGH, because the internal resistor
> would brutishly pull the voltage up.

Or if the pin was connected to a relay or something. This is why most of 
the pins default to high-impedance input after a reset.

Martin