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.

Initial Goals:
 - 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

Future Work:
 - 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!
<p>I have very low technical ability. Is it possible to use the Artisan software with a HMI and show it on the screen of the HMI?</p><p>Is it easy for someone with technical knowledge to do?</p><p>ian@helian.net.au</p>
<p>What an amazing project, and you have really done it well! </p>
Just wondering: the fan motor of my popper is a DC motor (bridged). Do I have to use a DC to DC solid state relay instead?
<p>Great Instructable!!</p><p>I'd like to add a warning for those hunting for the elusive Poppery I. There is a Poppery 1.5 out there. It looks just like the Poppery I, but it is only 1200 watts. It's not the Poppery II, it is identical to the original Poppery I. Be sure to check the bottom for the wattage. It's also lighter in weight, not as tank like as the original. They will still work for roasting but if you are paying a premium price for a Poppery I just double check.</p><p>I have 5 of them. Picking them up over the years, thinking they were 1500 watters. Not till I took one apart, to do a mod, did I realize the difference.</p><p>Thanks for posting.</p>
<p>I am living in Kigali and a small group of ex-pats buy coffee beans from local farmers and washing stations. In 4 weeks I will be home and i will bring as many beans as possible just so i can build this EXCELLENT 'ible.</p><p>Thanks so much for the great documentation!</p>
<p>Fantastically detailed explanation/illustration of electronics. Way too much for me. I'd settle for just the SCR control of the heating coil. The fan can be left as is or at a fixed higher voltage to speed it up. It's the heat that needs to be controlled.</p><p>I don't know why you cannabalized the unit. It is fine as is and the dome funnels the chaff to a container. I have a cheap popper I got at Goodwill and all I did was place a screen over the top opening to prevent melting and let the 'hood' do its job of directing the chaff to a big metal bowl.</p>
<p>Fantastic!</p><p>I really enjoyed reading all the project steps and I like very much the work done.</p><p>To me, as a home roaster, the small quantities are not a problem and I appreciate the easy control of hot air poppers (manually so far) with good roasted beans for my Gaggia grinder and La Pavoni pro. </p><p>A Laptop control is a dream of mine.</p><p>I have a question, please, can I use the same components in a 220-240 Volts (Europe standard) environment?</p><p> Thank you</p>
<p>Looks great, the only drawback to the air popper is how small the roasting batch is. I've moved to a Stir-Crazy / Turbo Oven and am roasting 12 - 16 oz, now I have to consider adding the control you have outlined here to the Turbo Oven!</p>
<p>Great point! The control electronics described in the Instructable can be applied to many different roasters. Most popularly, home roasters like to modify the HotTop roaster. Does the Stir-Crazy have an AC motor or is it a DC motor with a bridge rectifier at the motor inputs?</p>
<p>Glad to see someone expanded on this topic. I had been told an air pop machine could be used to roast the beans but without alteration of the machine. The results were burned beans, smoke and a lot of concern from the neighbors due to the acrid smoke/smell! Thanks!</p>
<p>Fantastic instructable! Great job on explaining all of the electronics.</p>
<p>Was I the only one who thought that it looked sorta like a dummy?</p>
Wow, excellent ible! I have long contemplated home roasting, but it always seems like one thing too many... However, very inspirational!

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