I did try 5V, didn't work for me. Interested if you test.

Didn't understand the 2nd bit... No need to sink any current. Passive state is high Z. Active state sources current. Issue I had is that 5V doesn't seem to be enough to toggle the input stage. If you can get it to work, all the resistors & transistors involved with the TX can be removed with just a small bit of software change. I power the NANO through USB. There are some voltage losses through the chip and also a diode to permit other power schemes. Powering with the NANO regulator might be enough to make it work. So there might be a way, but I didn't look too hard. I also needed to buy the zener. Can't just buy one on the 'zon so i have a bag full.

-T