Is there any way to use analog temp sensors (RTD or TC) with the Brewpi Spark? Some sort of ADC device to take the analog data and convert to the digital?
I’m thinking of a weird Kal/Brewpi hybrid build, and would like to only have one set of sensors…
You would need to use a converter chip, like this one:
http://www.maximintegrated.com/en/products/analog/sensors-and-sensor-interface/MAX31865.html
Unfortunately Maxim does not make a OneWire version.
In the future I might release a board with this + a small microcontroller + RS485 to talk to the spark core.
But the interface to the thermocouple would cost much more than a OneWire sensor, so I am not sure it is worth it.
Why do you want it to be hybrid?
Insanity, mostly 
My original thought was to build a KAL system. But I like the automation idea. So I thought I’d build a KAL that allowed me to add an automatic controller afterwards.
Yes, I know, it’d be easier to just do one or the other…
I would love to see RTD (PT-100) A/D converter so that those of us that built the electric brewery can easily upgrade. The RTD sensors were quite expensive (ca $35 each iirc). RTDs are a clear win over thermocouples, but I’m not sure they are superior to the semiconductor bandgap sensor in the DS18B20’s. Anyone know?
I totally have to agree @mdma I have a lot already invested in fittings and sensors so the ability to integrate into my existing would be really nice and save me a good bit of $$.
Sounds like the answer is 1) the Max 31865 chop Elco mentioned, 2) an Arduino (or other microcontroller, but I’m used to Arduino), 3) code for the Arduino that emulates a 1-wire slave (see here: http://forum.arduino.cc/index.php?topic=65706.75).
Using a small Arduino, like the Pro Micro, it’d be a pretty simple build. Maybe.
That should allow plug-and-play compatibility with the BrewPi, I think.
May have to play with it someday…
I cannot sell a custom OneWire slave. Not allowed by Maxim.
So my solution would communicate over RS-485, and this is one of the reasons I put it on the board.
So I would make a custom board with a small AVR, a MAX3082ESA for rx/tx to RS-485 and the MAX31865 as a OneWire interface. It probably makes sense then to put 2, 3 or 4 MAX31865 chips on the board. Unfortunately, it is not a cheap device.
So there’s no way to market a custom 1-wire slave device? That’s kind of annoying…