I have a passion for coffee. I also have a passion for electrical engineering. Why not combine them?
This Instructable describes how I transformed a hot air popcorn popper into a completely controllable coffee roaster! Follow these instructions to re-purpose and hack your West Bend Poppery Popcorn Popper into this coffee roaster!
The extraction of the complex aromatic and flavor characteristics of a coffee bean is dictated by a roaster’s ability to control a variety of variables that act on a green coffee bean while it is roasting. Not only must one understand certain audible and visual cues from the beans during the course of the roast, but the roasting apparatus must also react to changes to the fan speed and heater power in order to change the temperature inside of the roasting chamber. At the same time, the roast logging software must be displaying a graphical summary of the temperature in the chamber versus time, also known as the roasting profile.
This feat often necessitates the purchase of an expensive programmable roaster; but, a modified popcorn popper can rival the functionality of a high-end programmable roaster if adapted with internal temperature sensors, a reactive control system, and the ability for the software to save roasting profiles for later use. This modified popcorn popper will automatically control the temperature and total roast time based on industry roasting profiles; component costs will remain under $360; and a taste comparison between beans roasted in a modified and unmodified roaster will be completed by an experienced coffee taster.
Upon submission of this Instructable, the roaster has the capabilities of controlling both the power to the heater coil and the speed of the universal AC/DC motor that is used to blow air over the heating coil. This air is blown into the roasting chamber where thermocouples are sensing and sending temperature information to a microcontroller which is interfaced with a roast logging software called Artisan. This roast logging software displays the temperature versus time inside of the roasting chamber while also providing functionality to the roaster user to adjust the percentage of power going to the heater coil and the percentage of speed that the fan is spinning.
Step 1: Identifying Design Goals
Before getting into the hands-on work of the project, I had to identify the features of the coffee roaster that I wanted to implement into the popcorn popper.
- Heater control and fan control to adjust the temperature inside of the chamber.
- Interface with a computer to log the roasting profile.
- Manually control the heater power and fan speed using the computer roasting program
- Ability to save roasting profiles to use for another roast.
- Remain under $500 in total component cost
- PID Control of the Roaster
- Chaff Collection
Why did I choose the West Bend Poppery I?
The Poppery I is a 1500 Watt model. The Poppery II is a 1200 Watt model. The Poppery I uses a universal AC/DC motor, while the Poppery II used a DC brush motor with a bridge rectifier (to convert the AC to DC). Having the 300 extra Watts will allow this popper to reach higher temperatures and the induction motor of the Poppery I is easier to control with the components chosen for this project!