PID-controlled ceramic smoker

When it comes to home smokers, everyone wants a ceramic unit – their heat retention is unparalleled, meaning it takes less fuel, less smoke, and less of your attention to cook the same mass of food. Kamado-style smokers and the well-known Big Green Egg are ultra-high-end, and their prices show it. I was inspired by an episode of Alton Brown’s show, Good Eats, to develop my own solution with what I could source. However, I needed my smoker to be large enough to hold two full racks of pork back ribs (about 18″ long racks) a couple of pork butts, or a medium sized turkey.

Nothing here for under $1000. Photo credit: AmazingRibs.com

The single hardest task was finding somewhere near Athens or Atlanta that sold enormous, unglazed terra cotta flower pots. As an academic researcher, I have pretty well-practiced Google-fu, but it took me several weeks to find a 19.75″ diameter pot, a ‘low bowl’ that nests with the pot (for the lid), and a grill grate that perfectly fits the inner lip of the pot. I found the bowl at a local pottery yard but I had to order the pot from simplyplanters.com ($70 including shipping).

Local pottery yard, full of proud elephants

Grill grate fits like a damn glove.

While ribs are a relatively fast-cooking cut of meat like steaks, beef brisket, a delight I had never cooked before, is a very slow-cooking cut. If done properly, smoking a whole point or flat of brisket would take upwards of 12 hours and I did not want to have to actively tend the smoker all day.

15 hours cook time. Worth every minute. Photo credit: AmazingRibs.com

Since the smoker has an electric heating element, I realized some sort of thermostat could could solve the problem (set it and forget it!). My research turned up the versatile PID controller, an off-the-shelf microcontroller that uses an advanced algorithm to maintain the programmed temperature parameter without overshooting – perfect for achieving and maintaining a low smoking temperature. I initially learned of the idea from Seattle Food Geek – he had already utilized a PID for application in sous vide, and I adapted the electrical design to suit my needs. I wanted to make a modular controller box with a clean design to allow quick swapping of hardware components like heating elements (if I ever chose to dabble in sous vide).

I got all the electronics together and tested everything – not on a breadboard, because of the scale of components, but on a piece of cardboard. I ensured all wiring and connectors near or inside the smoker were high-temperature rated and then started looking for a case. I wanted the unit to be as small as possible, while providing adequate heat dissipation for the solid state relay. Off-the shelf ABS enclosures, or ‘project boxes,’ looked cheap and ugly and were priced much too high for what you get. Aluminum enclosures I found were always too large or too small and hugely expensive. And with either, I would have to worry about cutting holes for various components: the female AC socket, the GFCI outlet, the PID controller, and the toggle switch.

Hideous or expensive, take your pick.

Considering the prices I’d seen for off-the-shelf enclosures, custom laser-cut acrylic enclosures were actually priced competitively. They also offered an attractive level of customization: the perfect size, precision cuts for perfect fit of components, and the ability to engrave text or images. I would simply have to design and optimize (re: minimize) the cuts and materials needed with a .svg editor like Inkscape. I learned Inkscape slowly over a week’s time, working to design a glue-less, T-slot enclosure that would only require nuts and bolts to assemble. (Update Nov-2014: where was this software tool when I needed it!?)

Custom laser-cut enclosure, thanks Ponoko!

Originally I wanted to make a big, creative raster on the side of the enclosure, but when I submitted the design I learned it would add so much laser-time to the job that it doubled the cost, so I skipped it.

Sample rasters/engraving. Photo credit: Ponoko.com

I’ll admit that I saw this slogan on a sign outside a BBQ shack on the drive to Suches, GA, but the proud pig is my own addition

If I had to do it over again, I would make the whole thing out of P1 sheets of acrylic, reducing cost and giving the enclosure a more cubic form. I also selected the cheapest acrylic (3 mm thick), which is slightly regrettable because there is too much flex at the centers of the top and bottom acrylic panels for my liking.

PID controller (press-fit) and toggle switch fit perfectly

Rear of unit has GFCI outlet for heating elements, female AC socket for power, and 3.5 mm stereo jack for the thermocouple

Fully assembled unit, approximately 3″ x 6″ x 10.5″.

The PID controller software requires one-time calibration (re: set the temperature and select the auto-tune function) to your smoker’s internal volume and choice of heating element. Once this is done, just select your cooking temperature and add a couple of hardwood chunks to the pan every 3-4 hours. I typically get an overshoot of less than one degree Celsius.