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Coffee Roasting with an Arduino Based Rate-of-Rise Meter

August 14, 2010

That’s my Hottop KN-8828B drum coffee roaster with a pair of thermocouples measuring bean temperature, one to the new Arduino based project, one to my old Fluke which its about to replace.

The “TC4 Shield” project started on, the “shield” designed by Jim Gallt, and the Arduino and Processing code is open source, c/o Jim and a few others. Its all very polished.

Besides being able to plot the data over time from up to four thermocouples (lots of homeroasters just use two, patched into two meters), the project also calculates the “rate of rise”, a critical variable in the coffee roasting profile, and one that is typically a PITA to chart manually.

Soldering was pretty easy thanks to a well designed and silk screened board, even with a cheapo soldering pencil, and components like this MCP9800 surface mount. I did manage to fubar the solder connection on one of the MCP9800 pins, but it was pretty simple to resolve with some debugging to the Arduino code and a DMM to check continuity, which I should have been doing all along.

Here’s the output (also available as CSV), captured via the Arduino over USB to Processing showing the bean temperature over time (in red) and the rate-of-rise (in green). The currently unused channel in yellow will soon be plotting results of environmental temperature, mostly to make sure my ET isn’t dropping when I rapidly lower the heat half way though first crack, as a sanity check to make sure I’m not doing anything I shouldn’t be.

Besides the addition of the ET probe, I also need to wire up the 16×2 LCD, come up with a decent enclosure, and rewire the two thermocouples to be unpluggable, which should all be pretty simple. I’m also a few revs behind on the Arduino, which is a quick fix, but not reflected in the above chart. The latest rev supposedly smooths out the rate-of-rise.

There’s currently some work being done to turn the TC4 shield into a PID. So instead of just data logging, it could be wired into the roaster to manage heater and/or fan control. My stored profiles in the Hottop are dialed in pretty well, but they Hottop doesn’t correct for things like changes in environmental temperature (either summer to winter, or a warm drum from a just completed roast), or changes in charge size (weight of beans you start with)- so I suspect a conversion to a PID is in my future.


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  1. Sweet! Are you at the point where you will start to adjust your roast profile based on the data the has been collected?

    • I think the addition of the environmental temp. data may cause me to adjust my profile, but so far its not capturing anything I didn’t already know via the multimeter and a logbook- it just makes it way easier to see and record.

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