Since the previous post I made a bunch of changes to my modified Popcorn coffee roaster. Roast visability, Control + repeatability, increased capacity

TC4+ and artisan

I took the plunge and bought a TC4+ kit from Matthias . This is basically an arduino circuit board that you allows you to monitor and control a coffee roaster. (Basically it can read k-type thermocouples and control AC and DC loads, and can interface with the excellent + free/opensource Artisan Software)

TC4 plus

I bought the kit board version because it was cheaper and gave me an excuse to buy a cheap soldering iron and learn to solder (thanks youtube!). I also bought a cheap SSR to control the heating element and some k type theromocouples.

If you were trying to do this on the cheap you could probably just use an arduino, a max31855 thermocouple breakout board and an SSR, but you’d need to write some code to get that stuff interfaced to Artisan. The TC4+ board has a bunch of software and plays with Artisan easily.

Monitoring a manual roast with Artisan is really nice compared to writing down the temperatures every 30 seconds. Setting up the PID controller so that the heater drives a pre-defined temperature curve is also fairly straightforward. GreenCardigan has some nice videos about it here and here.

half the price of the fully assembled version (45 quid), though I didn’t have any soldering experience. Thankfully it wasn’t that difficult to solder the thing together with a cheapo iron, especially after watching some youtube videos on soldering. I was concerned that I’d burn out the components with the amount of heat I was applying but it seemed to be fine.

The main reason to have the TC4+ board is to hook the fan and heater and up to the opensource Artisan roaster-scope software. My original motivation was to have it automatically record the manual roasts I was doing (rather than writing down numbers every 30 seconds), but it wasn’t long before I experimented with the artisan PID controller features and never looked back. I found a youtube video about configuring the pid stuff once the board is connected.

overcoming the some limitations

Getting more air

As far as I can see, the airflow dictates the quantity of beans you can roast in a single batch. If there’s not enough airflow then the beans aren’t moved around / agitated enough to be roasted evenly. There might be such a thing as too much airflow, but I don’t know enough about roasting to assess that.

Some green coffee’s seem to be much lighter than others. I guess this is a function of size and moisture in the variety.

Anyway, running the fan motor at the stock 20v I found the severin could only just mix around 85g of greens. This capacity increases as the beens cook and the moisture evaporates out of the bean, and there are a lot of suggestions/accounts of stirring the beans by hand when they are green until they’ve got light enough for the popper to do this unaided. I’d like to be able to roast coffee with minimal manual effort, so I’ve been looking to improve this.

You read a lot of suggestions to hand stir the green beans at the start of a roast until they loose enough

One way to get more airflow is to run the motor at a higher voltage, and as I mentioned in the last post I routinely run the motor at higher voltages. However the biggest improvement to airflow came from simply bending the airvents in the chamber to make them bigger. I can’t claim

Getting more heat

With the fan motor turned up above 24v the Severin element struggles to generate enough heat to get the beans above the 210c or so for first crack. The best way I’ve found


I don’t know why it didn’t occur to me earlier, but the