Tiny Cheap Fluid Bed Roaster by Tije and Jan

(also see Daily Coffee News feature)
Tije designed and made the following structure for a tiny and cheap fluid bed roaster, to which Jan van der Weel added the Arduino parts, electronics and programming:

Sketch by Tije de Jong

Jan sourced a very cheap blower (€ 11) to start with, Tije developed and constructed the mechanics, Jan built together and programmed the TC4 / SSR electronics. 

On his blog, Jan will specify exactly how the TC4 part is combined and programmed and I will copy these details into this blog entry, just as Jan will use this video in his blog.

We did a few test roasts to make sure it works at all and it does. Towards the end, the first roast tended to get a flat BT line and airflow was slightly decreased. 200g seems max load of green beans. Second roast a little more power was given to the heater. Next we will try the Background Roast driven by the PID software of Artisan.

A week later, with updated software that works better to change the fan speed in a stepless way:

Vimeo version:

(Adding the following contribution by Jan van der Weel)

Hardware and electronic design

(copied / merged from http://www.byleew.nl/coffee/simple-affordable-fluid-bed-roaster/)

Essentially the electronics for this design consist of a heating element, air pump, two relays and a temperature probe. The hardware design is inspired by the Roastuino project. In this project they used a simple heating element (heat gun), glass roast chamber and cheap (€ 12) but effective air pump. For the ‘electronic heart’ we used TC4 Digital Thermometer and Temperature Controller. The advantage of the TC4 is that it’s relatively cheap, programmable and it already has existing firmware to make it work with the Artisan roast software. After sourcing all the hardware, Tije manufactured the remaining parts and he also constructed the prototype. We used a very helpful wiring diagram (use at your own risk) that we found on the TC4 site to connect the electronics.

Firmware for the TC4

Without firmware the TC4 will not do anything. Luckily there are different firmware versions (Artisan Arduino Sketches) for the TC4 available. First we tried the latest available aArtisan that we found on this TC4 site. The code was from 2013 and we somehow did not get it to work properly. On Github we found a more recent version (aArtisanQ_PID_6_0). After compiling the Arduino sketch made by Jim Gallt we got a warning ‘Low memory available, stability problems may occur’. Maybe the code needs to be optimised, but we just hoped it’s would not be a problem.

Second test

Last week, we tested the roaster again. The airflow and heating are nicely balanced. When using 100% power from the heating element, we were able to get 200 grams of coffee in first crack after just 4 minutes and 45 seconds. That means that the machine has lots of power. The prototype was able to communicate with the Artisan roast software. We could log the temperature and set the heating percentage. The AC fan control however didn’t work. This problem was solved by installing the newer firmware .

Logging noise

Next steps

More work needs to be done. Priorities are to configure the PID temperature control and to reduce the logging noise. Many thanks to everyone that have made this project possible. To be continued!

List of parts

Below you can see the list of the parts that we have used until now. When you add up all the costs you can see how it somehow got a little more expensive than we had hoped.

Table: List of parts

Number	Components	Quantity	Order	Euro (ex shipping)
1	Fotek SSR 40 DA	1	Ebay	4.15
2	Crydom d2425-10	1	Ebay	25
3	AC zero cross detector	1	mlgp-llc.com	21.5
2	TC4 SHIELD	1	mlgp-llc.com	79
3	Silverchrest Air Pump	1	Ebay	12.9
4	Ceramic Heat gun element 30 Ohm	1	Aliexpress?	0
5	Laboratory heat resistant glass (90 mm x 2.5 mm x 200 mm)	1	Lgsbv.com	79
6	Funnel (inner diameter 97mm)	1	?	7
7	Heat resistant kit (Uni Acryl AC 180)	1	Kachelmaterialenshop.nl	12.2
8	Jumper wires	1	Ebay	0
9	Tube mounting brackets	1	?	0
10	Wood	1	?	0
11	K-thermocouple (miniature)	1	tcdirect.nl	22
12				262.75

PS Update on Sept 16, 2016:
Today, Jan updated the Arduino software, also trying out a new Artisan setup that supports a "background roast" using the Artisan PID to follow a pre-designed roast profile. The background is not followed yet so we missed a setting but the PID keeps a fairly stable target temperature. Tije fixed the new safety switch that Jan has brought along. In case of software failure, if you want to switch off the heater and keep the blower active in order to cool the beans and prevent overheating of the element, the switch bypasses the Arduino control board.

PS 4 October 2016:

 Text and screen snapshots by Jan van der Weel.

Yesterday we tested the “background roast” feature of the free Artisan software, with Artisan activating and regulating the heater in order to let the BT cruise along the pre-designed profile. Before our test made a few improvements to the hard- and software configuration.

Closing the air leak
Tije sealed the edge of the funnel to fix an air leak. This change boosted the power of the airflow into the bed of beans. Our first impression is that the maximum batch size increased from 200 grams to at least 225-250 grams.

Fighting spikes
In our last test drive we experienced a lot of spikes in the temperature readings. To fix this we installed two ferrite beads that were supposed to suppress the high frequency noise in the circuit. Marko Luther, also gave us suggestions how to get more stable readings. By increasing the filter values in the Artisan Device Assignment tab, we should get better usable readings. Marko indicated that a value from 80 until 90 percent should give us better results. These changes resulted in much more stable readings.

Improving Device and PID configuration

In our previous test we didn’t manage to let Artisan drive the PID drive the roast along the pre defined roast curve. After showing Marko Luther our configuration files, he quickly saw what caused the issue. The PID settings on the Arduino control tab had to be reconfiged. To make it work the source number needed to be changed into “2”. That’s the same as the BT channel number on the Device Assignment tab. Many thanks to Marko Luther for his great help!

Testing roasting along the pre defined roast curve

During the preparation of our test we saw chaff flying into the air pump. This chaff decreased the power of the airflow. Frans fixed this problem pragmatically by installing a little strainer on the air pump.

After making all of the changes we were ready for the ‘background roast’ test. The test was quite successful. We managed to get our prototype to roast along the pre defined roast curve. The graph shows that the PID follows the background. But in the image below that the precision can be improved. In graph below you can also see a big dip after the start of the first crack. This might have been caused by airflow changes during the roast.

Next steps

More work needs to be done to optimise the PID configuration. Furthermore we are planning to put a kind of hood on the roasting chamber. This is supposed to improve the efficiency of the heating by restricting the loss of hot air. We are looking forward to do the next test run!