Building a better PID smoker controller

[Matt] wanted to have more control over his meat smoker so he built this advanced PID smoker controller. It uses the solid state relay seen in the bottom-right of this image to switch the smoker’s heating element. But all of the other goodies that are included add several features not usually found in these builds.

This is a replacement for the commercial PID unit he used on the original build. That monitored the temperature in the smoker, using predictive algorithms to maintain just the right heat level. But this time around [Matt] is looking for extra feedback with a second sensor to monitor meat temperature. Using an Arduino with an SD shield he is able to data log the smoking sessions, and his custom code allows him to specify temperature profiles for resting the meat after it has hit the target temperature. It kind of reminds us of a reflow oven controller… but for food.

Comments

  1. d hamilton says:

    Where did you get the thermocouple cables ??

  2. wulfman says:
  3. d hamilton says:

    wow, lots to choose from.

    Please the model number.

  4. Matt K says:

    I just used overpriced amazon k-type thermocouples that I already had lying around. This isn’t a particularly precision-necessary application, so pretty much anything that will cover the intended temp range will work fine.

  5. Cheeng says:

    Anyone have a tech document or something similar detailing the basics of an embedded PID program? The P is easy. The I and the D I think would be approximated by using known time steps. I have been curious about this for a while. Could not think of a better time than now to ask. :D How did you set your constants for your smoker?

  6. purdue says:

    I am actually doing something like this for a school project. Mine uses a triac with a look-up table for linear phase angle firing correction, zero-cross, a VB GUI for remote control/monitoring, LCD and buttons for local control/monitoring, wireless transceiver, PID… meat and smoker temp via DS18S20 one-wire, all on a MSP430G2553 with the Anaren CC1101L radio. It holds the temp easily within a degree right now in prototype stage (I’m integrating this coming week). There are profiles to start smoldering the wood chips and for once the meat is done as well. I’ll think about posting something once this semester is done and I graduate. Perhaps my formal report as well as some more interesting (aka: non purely academic) information.

  7. Matt K says:

    Autotuning, wild guessing, and a system that has a fairly slow and damped response. In short, I really have no idea if my values are set up “correctly”, but they work. Or at least I think they do. The datalogging capability should help me see how good it actually is.

  8. josh says:
  9. Hackneyed says:

    As a BBQer, these projects are always welcome.

    I’m playing with gas at the moment. Unfortunately it is far more tricky to do cheaply or simply because bad stuff happens if your fire goes out and propane collects in the smoker, etc.

  10. Hackneyed says:

    Instead of buying a relay, how about using a cheap servo from the parts box to flip a switch, or power strip?

    Ultimately a relay would be better, but a switch flipping servo would allow fast prototyping with less investment.

    Bonus points if the switch is mounted on a little wooden smoker control box, with a hand that comes out of a trap door to flip it.

  11. tempinator says:

    Given the low temps in this application, why use thermocouples?

    Why not just use any of the cheap solid state sensors? You can buy them pre-packaged really cheap.

    If you need to monitor a firebox, etc, then you may need a real therocouple.

  12. Matt K says:

    the temps are low, but the environment is fairly nasty, with a lot of humidity and (obviously) smoke, as well as meat juices. The stainless steel thermocouples handle that stuff very well. But yes, you could do it a bit cheaper with a solid state sensor.

  13. Matt K says:

    actually, I am not sure how cheap a solid state sensor that can handle 400+*F is either. I usually smoke down around 220 or so, but occasionally I do something hotter.

  14. cbob says:

    VERY cool.
    Low temp alarms & maybe a auto-shutoff for a propane based system. (servo connected to a lever shutoff?)

    Lots of heat, humidity, grease, ashes & salt from any saline injections or rubs. Citrus based marinades would add acids into to mix as well.

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