Intermittent functionality of both sensors running on the same pins

[codebru]

Issue

I have have intermittent issues running the sensors on the same pins (bus). In simple terms, if both sensors run off D1 & D2 neither give a coherent output. I have managed to get it to work in my home prototype but this needs to be reviewed - hence intermittent.

Debug Information

Pending

---

Note: Apologies for the not very fleshed out ticket I still need to dig more in to this, I just didn't want it to be forgotten.