I own a small coffee roasting machine (a "Röstmeister") that can be told to roast raw coffee in seven steps, increasing the duration (and? or?) temperature of the roast. Heating happens through a hot-air nozzle.
It would be nice if this device could measure the temperature of the coffee beans, and adjust the air heating accordingly, creating a programmable temperature curve in the roasting process.
In a first step, I might add a temperature sensor to the roasting chamber, and find out how good the "builtin" temperature control is. If this is found insufficient, I could improve the heater control electronics.