I'm an avid owner and user of a Big Green Egg (www.biggreenegg.com). The BGE works great as both a grill and a smoker, capable of achieving very high temperatures (750+ deg F) for steaks, and very low (200 deg F) for ribs, brisket, and pork butt roast.
The ceramic walls of the BGE keep charcoal usage low. You can run the smoker well over 24 hours at low temperatures off a single load of charcoal. The biggest problem is that the Egg is a little too efficient for the Texas heat. I find it difficult to keep the fire low enough without causing it to go out.
The solution is RIBS, the Remotely Interactive BBQ Smoker. RIBS is an active temperature controller specifically designed for the Big Green Egg. RIBS is capable of maintaining the temperature of the smoker within +- 2 deg 90% of the time, preventing flameouts and temperature spikes.
This page details the RIBS design. Interested BGE owners may be able to use this information as a basis for active control of their smoker. Most of the mechanical parts are available from your nearest Home Depot, or equivalent building supply center. Some of the electrical interface components can be found at Radio Shack, or any electronic supply.
I took advantage of some old electronic components I had around the house. As it is unlikely that others have these exact items, I cannot provide a 'turnkey' kit, or even exact design. If you want to develop your own controller, you will almost certainly need to adapt RIBS. If you don't have a Big Green Egg, but still want to have control over your smoker, this design should be capable of that, provided your smoker has the following:
1. Good control over the air supply. The controller is designed to regulate temperature by opening and closing the air draft for the fire. Extended temperature control requires an excess of fuel with the air supply the limiting element of the fire. If you have an inexpensive offset smoker, New Braunfels, or Brinkman, you will need to improve the seals on the doors to the firebox.
2. An easily adjustable single control for the air supply. You need to be able to push/pull the control to open and close it.
RIBS has three main components: the actuator mechanism, electrical interface, and control software. Each of these is described below. Click on any image for a full size view.
The actuator, shown in the figure below, consists of a swing arm moved by a modified cordless drill. The swing arm is shown as the vertical member in the center of the figure and the screwdriver shown at the right side angled toward the bottom of the swing arm. Connecting the screwdriver to the swing arm is a length of all-thread rod which goes through a nut glued to a small piece of right angle metal which is itself secured to the swing arm so that it can pivot.
Here's another view:
When the screwdriver is activated, it turns the threaded rod which pushes or pulls the nut causing the swing arm to move. Attached to the other end of the swing arm is a second length of all-thread which also pivots. the end of this connecting rod is attached to a small hinge which is clamped to the tab on the BGE draft door.
The horizontal member, which acts as a base for mounting all the components together as well as the swing arm are made from perforated angle iron. This gives me plenty of pre-drilled mounting holes to choose from.
Note that everything must be permitted to pivot. The includes the screwdriver, swing arm, and all attachment points for the control rods. This is a very non-linear movement and if you don't allow things to pivot, something will get jammed up.
Not shown is a potentiometer mounted to a bracket underneath the pivot point of the swing arm. The potentiometer shaft is connected to the bolt which is tightly fastened to the swing arm. As the swing arm moves, it turns the pot which provide the position feedback to the controller.
Here are some close-ups of the mechanism:
This photo shows the screwdriver interface to the swing arm. I put a rod coupler on the end of the threaded rod, wrapped it with a few turns of duct tape to match the diameter of the shaft on the screwdriver. I slipped the threads of the rod into the hexagonal hole in the screwdriver shaft (1/4 inch rod fits nicely) then used a piece of vinyl tubing slit along its length around the duct tape and the screwdriver shaft. A couple of hose clamps hold it all together.
The nut on the angle is glue on. I probably should have soldered it or braised it to the angle, but it is working for now.
This picture shows the end of the coupling rod connected to the draft door on the BGE. As can be seen, I secured the rod to a small brass hinge. The other side of the hinge is simply clamped to the finger tab on the BGE. This avoids drilling a hole in the tab and makes for quick removal of the mechanism.
This is a picture of the feedback resistor mounted to the swing arm pivot. At the top of the photo is the swing arm. I mounted a bolt through the swing arm and used the top nut to keep the swing arm from turning on the bolt. The lower two nuts are locked together on the bolt such that the bolt will easily turn through the angle iron frame. The bolt is long enough so that it extends below the two nuts. Another piece of vinyl tubing, a little more duct tape, and a couple hose clamps allow the variable resistor to turn with the swing arm.
As I mentioned, I use a modified cordless screwdriver. I purchased a cheap ($13.00) Skil screwdriver from Home Depot. When I took the unit apart, I was delighted to find that the whole thing is modular. You simply remove the five screws holding the case together, then remove the battery and switch mechanism. Everything just pops out. You are left with the motor and gearcase. I soldered wires to the motor terminals and ran them out the hole no longer occupied by the switch.
In order to activate the screwdriver, you need a means to switch 3-4 volts DC to the screwdriver. You switch polarities to reverse the drive. I used a couple relays which were activated by a +- 12 Volt output from an old antenna rotator controller. The feedback resistor was also wired to the antenna rotator and provided the same feedback as the original rotator. The controller was modified to replace the original control resistor with a connection to the output of a digital to analog converter card in my personal computer.
Software was written to implement a 'Proportional - Integral - Derivative' control algorithm. This technique adjusts the draft door opening based on the current temperature and how fast that temperature is changing. A screen view of the software is shown below.
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