Open Collector Outputs Using SoftwareSerial or NewSoftSerial

I'm using an Arduino Uno and I'm wondering if it's possible to setup an Open Collector Output using Software Serial. In case it's relevant I'm interfacing with a Parallax SoundPal. It works fine on the Physical Serial Port when I set it up as an open collector output but I'm not having any luck at all with software serial. I'd really appreciate any help anyone can give me on this. I've tried using a physical pull-up resistor instead of the built-in one but that doesn't work either.

The arduino doesn't have open collector outputs so the only way to get one is to use an external transistor. This will invert the signal so it must be inverted in the software by hacking the library or use another transistor before the open collector one.

The only open collector (well open drain really) OP on the Arduino is the TWI interface which you're not using. Do you have a transistor to get this open collector?

The internal pull up resistors are not applicable to this.


Apologies for not being clear. I don't have a transistor but I did get it to work with the physical serial port by enabling the internal pull-up resistor. I'm wondering if it's possible to do something similar using a software serial library since the arduino I am using only has 1 physical port and I need it for computer interface.

Here's what I'm interfacing with: