Resurrecting a Tonino Coffee Roast Color Meter


Recently, my Tonino coffee roast color meter, developed by the same team that develops the Artisan roasting software, began malfunctioning. Maybe you don’t know what a coffee roast color meter is and what its purpose is. Let me explain.

A coffee roast color meter gives insights into the roast color, and hence, the roast level of the coffee. This color is linked to the coffee’s flavor, fragrance, and mouthfeel. The color is useful in determining if the coffee has been roasted to the desired level, such as a light color for a delicate filter coffee or a darker color for a more chocolaty coffee with a rich body. A color meter is also a helpful tool for quality control once you’ve decided on your preferred roast level. The preferred roast level is subjective and depends on both the potential of the coffee bean and personal taste. So, a color meter is definitely helpful.

The Tonino is supposed to express roast levels numerically, for instance, 60, 92, and 116, corresponding to dark, medium, and light roasts respectively. However, a few days back, something weird happened. Irrespective of the roast color, the meter persistently displayed -127. This could not be right because anything I tried to measure, like white paper, black plastic, every time the Tonino gave the same reading (-127). Despite attempts to recalibrate the meter, the problem persisted.

The Tonino was clearly broken. What could I do? Well, I like to make and fix things. So why not try to repair it?

The Tonino was developed by the same team that develops the Artisan roasting software, and I own the first version of this device. It was released as an open-source hardware and software project. This provides an excellent opportunity for repair because the hardware and software are well-documented on gitHub.

Besides the GitHub page, the question remained, how should I fix it? These were the steps I took:

  1. I initially suspected a faulty color sensor and decided to replace it using a spare one I had previously purchased. Unfortunately, the problem wasn’t resolved.
  2. I then hypothesised that the firmware on the Tonino may have been corrupted, leading me to consider replacing it, given that the source code is publicly available on Github. After making necessary adjustments to the code, adding the required libraries, and re-flashing the Arduino Nano board, which operates as the device’s brain, I was hopeful. The flashing was successful, and the Tonino desktop app recognised the color meter. However, I was still unable to recalibrate the device, and each measurement displayed a series of dashes. This wasn’t much of an improvement from the initial -127 error.
    Update: Marko Luther one of the main Tonino developers let me know that you can also  reflash the Tonino by using the Tonino desktop app. Marko wrote:

    Note that you can open the About box in the Tonino app (before connecting a Tonino) and do two right clicks until the app title reads “Tonino**” (note the two stars). If you now connect a Tonino it will re-upload the firmware even if that version of the firmware is already installed. No need to fight with the Arduino tool.

  3. I then considered a possible fault with the Arduino board, suspecting that the EEPROM, which stores calibration data, might be defective. The solution seemed to lie in replacing the Arduino Nano, connecting it to the other hardware components, flashing the firmware, testing, and reassembling.

Upon carrying out the steps as described under number three, the device began operating normally again. I could now recalibrate the meter and measure the color of my coffee roasts.

Repairability is a great thing, and it’s just great that all the needed information and source code was available on GitHub. Many thanks to the Tonino/Artisan team for their useful and affordable coffee color meter and all of the publicly available documentation.


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