Bean Mass Probe V2 – Basic Configuration

Some time ago I developed a bean mass probe for the Gene Cafe coffee roaster.  If you are familiar with  this roaster, you will know that adding a bean mass probe is a little tricky because of the way the drum rotates.  Basically, to make this work, you have to have a wireless temperature transmitter to get the data off the rotating drum and, additionally, you have to deal with the fact that the beans will not always be in contact with the thermocouple.

My first attempt at this worked pretty well using an Adafruit ProTrinket coupled with a Bluetooth board.  Recently, I developed the second generation of the bean mass probe using an ESP8266 micro controller (Adafruit Huzzah) that allows me to connect directly to the roaster using WiFi and MQTT.  With this I have now created a pretty slick Internet of Things Bean Mass Probe.

I’ve actually converted the entire RoastGenie system to IoT technology but that is a topic for another post.

The basic architecture of the system is shown in the figure below.  I host my own MQTT server (Mosquitto)  but I think you could easily use Adafruit IO as your MQTT broker.  I’ve not worked with this system but it looks like it has some nice features.   If you use Adafruit IO, I think you could access you live bean mass temperature data with a web browser instead of a traditional MQTT client (I use MQTT Spy). The real utility of having the bean mass probe use the MQTT protocol is that you can easily integrate the data into other systems (like the RoastGenie itself).


The bean mass probe consists of the following components: Adafruit Huzzah micro controller, MAX18255 thermocouple amplifier, and a LiPo battery.  The schematic is below.


Note: A previous version of this schematic I posted had an error (the power lead to the thermocouple amplifier was shown incorrectly connected to 3Vo instead of Vin)

These components are attached to the Gene Cafe on the rotating plate on the inlet side of the roaster.  The connection between the drum and the TC amplifier is done using mini K thermocouple connectors from Omega engineering to facilitate easy removal of the roasting drum.  The LiPo battery is attached to the roaster with a pair of Neodymium magnets so it is very easy to remove and recharge.


The thermocouple is installed in the drum as shown in this post.  This system works like a charm and is very tolerant to disruption in connections – unlike the Bluetooth version which would typically not reconnect if there was some problem (like a discharged battery).  I will try to get some additional details posted about software over the next several days — in the meantime, let me know if you have any questions.