In search of a perfectly-cooked brisket, [Aaron] recently completed this DIY PID-controlled sous-vide slow cooker. Sous-vide (French for “under vacuum”) is a cooking technique in which foods are typically vacuum-sealed and then cooked in a relatively low temperature water bath for an extended period of time. This is done to minimize temperature gradients throughout the food to ensure even cooking. Precise regulation of the water temperature is the key to ensuring that the results are exactly as desired – when cooking for many hours or days, even a few degrees discrepancy can greatly influence the final product.
A few months ago we featured a similar hack that utilized a simple switching temperature controller spliced into an extension cord. Although probably sufficient for most aspiring “hacker-chefs”, the temperature was not as stable as it could be. The problem is that it takes time for the heat generated in the slow cooker’s heating element to reach the temperature probe (and food) suspended in the water bath. By the time the probe reads the elevated temperature, the element is already too hot and the temperature overshoots the target. One way to mitigate this effect is to circulate the water to minimize temperature gradients, as is done in many of the expensive commercial units. In order to achieve similar results, [Aaron] instead created a PID controller that uses temperature feedback over time to precisely maintain the desired temperature and reduce any deviations resulting from outside disturbances.
The build is covered in detail and looks great in a custom acrylic enclosure. All of the board schematics, enclosure layout files, and source code are available under Creative Commons licensing at the bottom of his blog page. A good deal of time is also spent addressing the actual PID programming and tuning – something that could be useful for many different hacks requiring precise feedback control.
The end result is a professional looking control box and a slow cooker that is able to maintain temperature within 1°F even while using a DS1820 temperature sensor that is only rated as accurate to 0.5°C (0.9°F). From the pictures it looks like [Aaron] has finally achieved brisket bliss! Now the only question remaining is: what is the best setting for reheating left-over pizza?