You may be aware of our fondness for sous vide cooking here at PopSci. We've tested the Sous Vide Supreme, an off-the-shelf water bath cooker, and shown you how to convert your rice or slow cooker into a sous vide rig on the cheap. Now the good people at Make magazine have featured a nice-looking, built-from-scratch immersion circulator that, if you have the electronics expertise, can rival the expensive scientific equipment used by top chefs for a fraction of the cost.
Like most devices designed to keep a water bath locked at a precise temperature of your choosing, Make's rig uses a PID controller--a simple processor that turns the heat on or off to minimize the deviation between the actual measured temperature of the water bath and your desired setting. As always, Make goes the extra mile and gives you instructions on how to fashion a nice acrylic housing for the whole rig, which can be clamped to a water basin of any shape or size (an advantage over modding your pressure cooker).
That said, the project might be a bit over your head if, like me, you're not accustomed to reading wiring diagrams and slinging a soldering iron. And do keep in mind the finished product will be used in close proximity to lots of water--so you should be confident in the safety of your wiring. But the base price of just over $70 for all the components might be enough to entice the adventurous home cook into giving this a shot.
I built the controller and used it with an electric roaster for the water bath. It worked wonderfully! But it heated up the house and was too big for the kitchen counter. I got to thinking, air behaves like a liquid. I hooked up the controller to a large toaster/oven. It works just as well as the water bath, as long as the meat is sealed in a evacuated bag. Cooked steaks, beef roast, and pork roast to perfection. The oven sits on our counter top and does not heat up the house. It also works beautifully!!, without the water bath hassle. The controller keeps the temp within 1 degree f. and it just sits there for as long as we want to cook the meat. I thought of including a pic, but decided not.