The file driver is pretty simple, any external program can write a value in a textfile, and reef-pi can read it and use it as analog input. File path is configured during the driver creationAd a look but I don't think there's any way to setup a driver for pH that reads SPI, the drivers that are there seem to use i2c. There is a digital file option but not sure how to format the file and how it would work i.e. where does it live how do you clean it up etc. Oh well guess I just buy the ds18b20, its only $15 just wanted to use the probes I had here and it was fun to get the Analogue to Digital converter running. Might come in useful somewhere down the line.