A simpler sous-vide hack

Here are the contronl modules for a sous-vide project over at Nerdkits. [Humberto] and crew continue doing a great job of focusing a project on one goal, then explaining the steps needed to get there. In this case they wanted to build their own sous-vide appliance that was cheap, and didn’t really require the user to deal with mains voltage. We like it because most of the parts can be found at a hardware store and big box store.

He started with a slow cooker, which is pretty standard. Next he needed a way to switch power to the device. Instead of using a solid state relay, he went for a standard dimmer switch. It’s build into a double gang electrical box, and controls an outlet which is occupying the second position in that box. Now current to the slow cooker is limited by the position of the dimmer. The next task was to add a cardboard frame which marries a servo motor to the dimmer’s knob.

With the control scheme in place [Humberto] needed a feedback sensor. He built his own water proof temperature probe by covering an LM34 temperature sensor with shrink tube and sealing the ends. Just one probe in the cooking water isn’t very reliable so he added a second between the slow cooker’s base and ceramic vessel to improve the performace of the PID algorithm. He goes into detail about that in the video after the break.

Comments

  1. monopole says:

    It strikes me as a huge amount of obfuscation to get around dealing with line current and RTD or thermocouple probes. If you are terrified of mains voltage, get one of these : https://www.adafruit.com/products/268

  2. Sobachatina says:

    This is simpler? This is a cool hack but it can’t be called simpler than just using a relay. And what hardware stores sell off the shelf servos?

  3. aztraph says:

    Very Cool, or a hot idea, which ever way you go; but you need to take apart the crock pot because they don’t always have the heater on the bottom. most of the ones I have taken apart (and yes, i have done quite a few) have their elements on the side walls, it heats up a larger surface area and makes for more efficient use of energy. this knowledge will help you place your temperature sensors and even tighten the loop even closer, Commercial sous-vide measure in tenth of degrees.

  4. ColinB says:

    I fail to see how this is simpler than using a relay + temperature sensor.

    However, the thermal modeling using CircuitLab (online SPICE tool) is really interested and there is a lot of good information and analysis in the article.

    I was initially concerned about using a light dimmer switch with a slow cooker for fear of fire (thinking it might have a 1500 W element and overload the 600 W dimmer switch), but after a moment’s research I see that they consume less than 200 watts, so no problem there.

  5. macona says:

    Simpler? More like a rube goldberg device.

    Really, just buy a PID temp control off ebay and use that. About $20 plus shipping.

    And use a solid state relay. It gets annoying to heat the clicking of a regular relay.

  6. Jose.Torres says:

    The video presented is way more in-depth and educational than I expected it to be based on reading HackaDay’s description. This video by Nerdkits takes bachelors level material and puts it within reach of middle and high school students. Good job!

  7. conundrum says:

    You can get LM35 sensors from broken HP printers, they are mounted on a circuit board above the mechanism with a lid switch.

    Never had a bad one yet.

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