This was a project from May 2020 - prime lockdown insanity setting in, in the house 24/7 working, living, sleeping, no relief! Lots of wee projects up and down the country and this was mine. An effort to learn a bit more about about arduinos led to this idea for a small fluid-bed roaster.
The Theory
The beans need to be mixed and heated over a period or about 10 minutes. the more mixing the better, and the temperature has to be precicely controlled to different values throughout the 10 mins. Hijacking a popcorn machine was my plan, as it already had the heater and the fan, heating and mixing the wee kernels about. I thought i could just put a controller on the heating element and that would be that.
Fan
As it turns out, green coffee beans are a lot densetr than popcorn kernels, and so had to replace the fan with a bigger one - I chose a air bed inflating pump. Ran the supply through a dimmer switch and controll the dimming with a digital pot through the arduino.
Heater
The heating element was easy - ran the supply through a solid state relay, which is switched on and off by the arduino. With that, PWM means i can throttle the power from 0 - 100% with the arduino
Thermocouples
One at the hot air going in to the beans, and one at the air coming out. This lets me control the dT so as to not burn the beans, and the outlet is a proxy for the beans internal temp.
Controller
With temperature probes, and control of the heater and the fan all within the arduino, I just needed a brain for the recipes. Theres an industry standard software for this already in existance, called ‘artisan’, so i decided to use the arduino as a bridge between the laptop and the hardware. This lets me put in a curve that the temperature should follow, and it controlls the heater and fan to follow that curve!
The Results
Works a treat and tastes great! Bit of a pain at only being able to roast 100g at a time. I think of this as a proof of concept… I have dreams of a garage with a leaf blower based roaster kicking out kg’s at a time…
