Dave, aren't the analog temperatures converted to digital before they are passed on to the rPi? If so, with a standalone HM the digital temps are just going nowhere? So isn't it possible to use a stand alone HM at the grill and have the digital temps sent via wireless to the main HM that has the rPi? (perhaps not without some coding, but it could be done, right?) If the standalone HM was controlling the pit you wouldn't need to convert the fan/servo data to digital at all, you would just need to transmit the setpoint from the HM+rPi to the standalone HM I would think, from there the hardware on the standalone HM could manage the blower/servo to hold that setpoint.....
I realize this isn't doable with the existing code, but Bryan had been working on the wireless probe concept already... I thought perhaps a wireless standalone HM would be more useful and perhaps more worth the time than a wireless probe... cause after all, if you have a wireless probe you still need a HM board at the grill to control the pit.
As for power, yah, you are always going to need power at the grill and therefore at least 1 wire. But having to plug in the controller at the grill isn't a big deal, and I had given some thought to using a battery and solar cell to recharge it, which would give you a completely wireless grill connection....
As far as working with existing code, what I have come up with is to just use a cat5 cable from the HM+rPi and use the 8 wires for:
Servo Signal
Servo/Probe(s) Ground
Servo +5
Blower Signal
Blower +12
Probe 1
Probe 2
Probe 3
This will theoretically run the whole pit with 3 probes over 1 cat5 cable, though I haven't tried connecting any probes over the cat5 cable yet. I just ordered some 2mm panel jacks that I am gonna wire to the CAT5 jack on the grill side, so I can plug the probes in there, then jumper those three CAT5 wires over to the probe inputs inside the HM, at that point I will be able to test the concept. Still have to get that cable into the house for winter cooks though, but don't want to leave a window or door cracked open.....