The Pi is simply a temporary data logger for this. I wanted something to hook up and pull the temp every second (using a thermo-couple wire laid on the heat plate under the coffee pot) and store it and the time in a CSV file for 24 hours or so.
Then I can look at it and say things like "that rise in temp from 180f to 451f in 3 seconds was due to the pot being removed. Ignore it unless the temp stays high. If it stays high for more than 2-3 mins, sound the alarm as someone left the burner on." and "OH-EM-GEE! The temp went slowly from the 180f to 451f over about 2 mins. Raise the alarm! The pot is dry and about to burn up!!!!" The coffee pot should keep the temp of the heat plate down to around the 200f area right up to the point of pot starting to run dry. In fact, next time ya hit the great outdoors, take a PAPER cup (not foam), fill with water and drop an egg in it and set it right IN the camp fire for breakfast. The cup will burn down to the water line and then stop. The water, being liquid, can't go over 212 so it keeps the cup too cool to burn. The coffee pot should have much the same effect (but I just don't yet know what temp it "idles at", how fast it climbs when the pot's removed vs how fast when it slowly runs dry, how fast it recovers when the pot's replaced, etc.
So once I have an idea of what fast climb in temp is OK and what slower climb is bad (I'll deliberately let a pot of plain water run dry for logging) I can then put it all over onto an Arduino as by now I just need current readings and a running average for the past 5 mins or so and no more need for any storage place. The finished project will run off an Arduino Nano clone (or even possibly a Digispark if I can squeeze the code enough) and run a few ws2812's as a timer display for "is the coffee too old, even if fairly full?"
I COULD have hooked up an SD card to the Arduino and data-logged off it but this has been a fun learning experience with the Orange Pi and seeing what works (kernel-based i2c seems fine for running a 2x16 LCD display) and what doesn't (SPI does not seem to work out of the box. I might get it to working later but simply am bit-banging the MAX 6675 and that's actually taught me more, programming-wize.)
Final BOM would be: Two push buttons (one to (re)start the timer and one to silence the alarm), piezo buzzer, Arduino/Atmel chip/board of some sort, MAX 6675 thermo-couple board & thermo-couple K wire, maybe 4-5 ws2812's (or even just one that goes from bright green to dim red before going out completely after about 90 mins of the one button's press), power adapter to fit the Arduino and a nice little case.