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Home-Grown Temp Controller (pics)

pezking7ppezking7p Posts: 132
edited April 2012 in EggHead Forum
**Disclaimer**
I am not selling anything or trying to make money in any way.  What is below is intended only for my amusement and hopefully to spark some interest in Do-It-Yourself type of projects for others, and let you know that just because you don't know how to do something, doesn't mean you can't learn.
****************


I love my egg, but after my first overnight cook it became clear that if I wanted to keep my sanity while doing these cooks, I needed a better way to control and monitor temps.  Obviously I looked at the bbq guru and the stoker, etc, and promptly choked on my own tongue when I saw the cost.  I'm not unfamiliar with the cost of commercial temperature controllers, but I'm still a cheap skate so I balked.  Being the hobbyist that I am, I decided to make a project of it and build my own controller.  I'll chronicle my mishaps in here, and I encourage anyone else who has done something home grown to share in here as well. 

Cliffs:
-Prices for commercially available temp controllers too expensive
-I decide to take on the hobby of microelectronics and build my own
-If anyone else has done anything similar, please share here


So with that said, I decided to build a simple controller that would only control dome temp.

Design Criteria:
-Must control from 200-300 degF, +/-5 degrees
-Must be buildable for less than $50
-Select components with future upgrades in mind (wireless, multiple probes, etc) where possible.

I don't (didn't) know any circuit design aside from basic college physics and what I have gleaned in the years since then, mostly a basic understanding of what components do.  I also have a very strong background in computer programming, which definitely helps a lot.  I got my parts last Monday and have spent a lot of time working on it since then (not to mention the research I put in leading up to that). 

What I have now is ready for testing, and I hope to post a short video of my testing later tonight. 

If anyone has questions, I'm happy to answer.  Also interested in input from people who already have temp controllers to hear what you like/don't like about your units. 


I spent a LOT of time trying to decide on fan specifications.  I eventually settled on this blower...as soon as I opened the package my heart stopped!  40mm seemed so much larger in my head!  Hope this little fan has some balls.
image


Here is the circuit on my proto board.  I'll eventually have to build this on a real PC Board and put it in an enclosure.  The PIC is the big thing on the left...it's mounted on a programming board so I can connect it to my laptop. 
image
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Comments

  • God bless you engineering types. We would certainly be in trouble without you but this makes my head hurt. To be fair, I feel the same way when I see these awesome tables everyone builds at home. I can't draw a straight line with a ruler so these projects are just going to have to be left to others.


    Keeping it Weird in the ATX
  • tazcrashtazcrash Posts: 1,851
    OK, been toying with this in my head. 
    Gotta read when I'm not waiting for a compile.

    Bx - > NJ ->TX!!! 
    All to get cheaper brisket! 
  • Good thing about actually understanding the science behind things is you don't need gods blessing. ;)
    Good point. Just not in my wheel house.

    Keeping it Weird in the ATX
  • dlk7dlk7 Posts: 1,038
    I'm impressed with your drive and determination.  Here is my input: I've notice quite a bit of condensation in the digiq dx2 adapter at the end of a cook.  Make sure you insulate your fan from any moisture.  I have an XL so I don't use the damper function (leave it wide open) but I'm told that for the large and smaller, you may need the dampening function to keep the temp within + or - 5 degrees.  I was going to trade out my digiq dx2 to the new wifi version but now that I have the Maverick 732 I just use it for my indoor view of whats happening.

    Two XL BGEs - So Happy!!!!

    Waunakee, WI

  • tazcrashtazcrash Posts: 1,851
    -Must be buildable for less than $50
    I spent a LOT of time trying to decide on fan specifications.  I eventually settled on this blower...as soon as I opened the package my heart stopped!  40mm seemed so much larger in my head!  Hope this little fan has some balls.
    LOL, @ the 40 mm fan.

    How will you be monitoring temps? I hope you have a spare probe. Those will add to the cost unfortunately. 

    Bx - > NJ ->TX!!! 
    All to get cheaper brisket! 
  • travisstricktravisstrick Posts: 4,895
    that thing looks like an IED detonator. You scare me, man.
    Be careful, man! I've got a beverage here.
  • that thing looks like an IED detonator. You scare me, man.

    =))

    You got that right.
    Keeping it Weird in the ATX
  • pezking7ppezking7p Posts: 132
    I'm impressed with your drive and determination.  Here is my input: I've notice quite a bit of condensation in the digiq dx2 adapter at the end of a cook.  Make sure you insulate your fan from any moisture.  I have an XL so I don't use the damper function (leave it wide open) but I'm told that for the large and smaller, you may need the dampening function to keep the temp within + or - 5 degrees.  I was going to trade out my digiq dx2 to the new wifi version but now that I have the Maverick 732 I just use it for my indoor view of whats happening.
    Thanks for the input.  I'll have to look in to the condensation on the fan, that's an interesting problem. 

    One of the reasons I picked the style of fan that I did is because it has very little area for air to flow through, but I'm definitely adding a damper just to be safe.

    Wireless is 2nd on the list of upgrades, after adding a meat temp probe and ramp-down function.  So much to do, so little time!
  • pezking7ppezking7p Posts: 132


    LOL, @ the 40 mm fan.
    How will you be monitoring temps? I hope you have a spare probe. Those will add to the cost unfortunately. 
    I went back and forth over and over again on fan requirements.  Is high pressure necessary?  What is the real flow rate required to maintain temps?  I eventually decided to just buy a friggin fan and work out the details later after testing.

    I also spent a long time deciding what temp probes to use.  Right now I'm monitoring temps with a j-type thermocouple because it's cheap and I had one available.  It also has the huge advantage of not breaking if the temp goes over 400F, and isn't nearly as fragile as a thermistor probe, so it should last basically forever.  You can find a j-type probe for $18, so I figured it was as good as anything for dome temp. 

    I've found food-ready thermister probes (meat probes) for $12 or so, but finding them wholesale is tricky.  I'd prefer to save time and use a j-type food probe, but these don't seem to be available affordably. I'll tackle that problem later. 

    If anyone knows a way to get temperature probes for $10 or less, I'd LOVE to hear about it. 
  • pezking7ppezking7p Posts: 132
    that thing looks like an IED detonator. You scare me, man.
    It's an IBD: Improvised Barbecue Device.  When the timer reaches 000, BBQ sauce sprays everywhere. 


    >:D<
  • dlk7dlk7 Posts: 1,038

    My digiq dx2 uses a 10CFM fan and works beautifully for my XL.  It can raise the temp plenty fast for my needs.

    Two XL BGEs - So Happy!!!!

    Waunakee, WI

  • travisstricktravisstrick Posts: 4,895
    that thing looks like an IED detonator. You scare me, man.
    It's an IBD: Improvised Barbecue Device.  When the timer reaches 000, BBQ sauce sprays everywhere. 


    >:D<
    BLAHAHAHAHAHAH I think I just pee'd in my pants. =))
    Be careful, man! I've got a beverage here.
  • fonemanfoneman Posts: 104
    I look forward to seeing the video and knowing more about your setup...

    john
  • stikestike Posts: 15,597
    impressive.  but can't help thinking it's easier (maybe only for me, perhaps) to learn how to dial in temps on the egg than to build one of those things from scratch.

    but if it something you like to do, why not, right?


    ed egli avea del cul fatto trombetta -Dante
  • tgklemantgkleman Posts: 215
    You can buy an Auber Pit controller for $100.  Or you can by their PID controller for around $39, but you will need a power supply, fan, and K type thermo couple. 

    I built my own as well, using Auber and a BBQ guru fan, but it wound up costing about the same as a BBQ guru system.  I designed mine to suit my tastes (dual temp probes, pit probe, set point temp and process temp readouts).  Over engineered, but I like it.
  • Doc_EggertonDoc_Eggerton Posts: 4,993
    that thing looks like an IED detonator. You scare me, man.
    Use the rake from your MRAP for that cook.

    XLBGE X 2, LBGE (gave this one to my daughter), MBGE and lots of toys

  • pezking7ppezking7p Posts: 132
    impressive.  but can't help thinking it's easier (maybe only for me, perhaps) to learn how to dial in temps on the egg than to build one of those things from scratch.

    but if it something you like to do, why not, right?


    For me it's mostly about making the temp controller rather than needing it.  I like learning new stuff and building things. 
  • impressive.  but can't help thinking it's easier (maybe only for me, perhaps) to learn how to dial in temps on the egg than to build one of those things from scratch.

    but if it something you like to do, why not, right?


    For me it's mostly about making the temp controller rather than needing it.  I like learning new stuff and building things. 
    Keep on building my friend. Knuckleheads like me need you people to build our toys (and houses, cars, etc). This is an art that is lost on me but I have full appreciation for those that it isn't. 


    Keeping it Weird in the ATX
  • JerkChickenJerkChicken Posts: 551
    Cool project...

    Hope you nail it!


    B-)
    LBGE, Weber OTG w/ Rotisserie, Weber Genesis S-330, Chargriller Duo, AR-15, AK-47
  • pezking7ppezking7p Posts: 132
    You can buy an Auber Pit controller for $100.  Or you can by their PID controller for around $39, but you will need a power supply, fan, and K type thermo couple. 

    I built my own as well, using Auber and a BBQ guru fan, but it wound up costing about the same as a BBQ guru system.  I designed mine to suit my tastes (dual temp probes, pit probe, set point temp and process temp readouts).  Over engineered, but I like it.
    Never heard of auberins before but I know I will be going back to their website to buy cheap thermocouple probes!!!! 

    If you add up everything I have in the actual circuit right now, it's about $30 (excluding development board, extra parts, programming board, etc).  I will be hard pressed to get everything else finished for under $50, though under $60 should be doable easily.  I hope those guys at auberins are making some money because it looks like they have a very good product. 
  • @pezking7p I'd like to see your program for PID control. http://en.wikipedia.org/wiki/PID_controller I'm planning to make a grill controller with an Arduino. Deciding how to anticipate the temp change resulting from an airflow change it the bigest challenge. A close second is connecting a thermocouple and accounting for the bi-metal intersection in the connection.

    I talk about components and price here:
    I finally took the plunge and bought my large Big Green Easter Egg from Roswell Hardware in Roswell, GA 03/31/2012
  • pezking7ppezking7p Posts: 132
    @pezking7p I'd like to see your program for PID control. http://en.wikipedia.org/wiki/PID_controller I'm planning to make a grill controller with an Arduino. Deciding how to anticipate the temp change resulting from an airflow change it the bigest challenge. A close second is connecting a thermocouple and accounting for the bi-metal intersection in the connection.
    I talk about components and price here:http://eggheadforum.com/discussion/comment/1177091#Comment_1177091
    Hey Richard!  I just saw your post in the other thread earlier today. 

    I'm actually not using a PID control technique...because I know very little about it, except that if your P-I-D settings aren't correct, you may not ever hit your temp, or even get close.  The other problem is that the P the I, and the D might have to change depending on temperature set point, slide/baffle position, shifting of coal bed, plate setter position, etc etc etc.  Because of this, I took a different approach.

    I'm assuming that the amount of air flow is proportional to how long my fan is on.  I'm also assuming that the increase in temperature is proportional to air flow.  So, what I do is monitor over a period of time, say 5 minutes, the total amount of time my fan has been on, and the total change in temperature.  I divide the two out and say that, for this moment in time, that is the relationship between airflow and temperature change.  I then use that number to adjust my current duty cycle to theoretically "zero change in temp" setting. 

    Additionally, I say that if there is a drastic temperature excursion at any time, the duty cycle is set to 100 (for low temp) or 0 (for high temp). 

    Now, I tested all this tonight and suffice to say, I didn't set my cycle times correctly, I need to make my logic a bit smarter and smoother.  I have a suspicion that I'm unintentionally designing a PID controller, but for now I'll start simple and get more complicated as necessary. 
  • pezking7ppezking7p Posts: 132
    Also, accounting for the connection in thermocouple measurements is called "cold junction compensation".  There are ICs that do this automatically, but they are very pricy ($15).  What I've done is use an IC that connects to V+ and V-, and has a single output pin with 10 mV/degC.  I assume the junction and the IC are at the same temp, as they are next to each other on my board.../shrug.  I could get more involved than that but it seems to work.  http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&itemSeq=112508189&uq=634683782363467494
  • tgklemantgkleman Posts: 215
    @pezking7p I'd like to see your program for PID control. http://en.wikipedia.org/wiki/PID_controller I'm planning to make a grill controller with an Arduino. Deciding how to anticipate the temp change resulting from an airflow change it the bigest challenge. A close second is connecting a thermocouple and accounting for the bi-metal intersection in the connection.
    I talk about components and price here:http://eggheadforum.com/discussion/comment/1177091#Comment_1177091
    Hey Richard!  I just saw your post in the other thread earlier today. 

    I'm actually not using a PID control technique...because I know very little about it, except that if your P-I-D settings aren't correct, you may not ever hit your temp, or even get close.  The other problem is that the P the I, and the D might have to change depending on temperature set point, slide/baffle position, shifting of coal bed, plate setter position, etc etc etc.  Because of this, I took a different approach.

    I'm assuming that the amount of air flow is proportional to how long my fan is on.  I'm also assuming that the increase in temperature is proportional to air flow.  So, what I do is monitor over a period of time, say 5 minutes, the total amount of time my fan has been on, and the total change in temperature.  I divide the two out and say that, for this moment in time, that is the relationship between airflow and temperature change.  I then use that number to adjust my current duty cycle to theoretically "zero change in temp" setting. 

    Additionally, I say that if there is a drastic temperature excursion at any time, the duty cycle is set to 100 (for low temp) or 0 (for high temp). 

    Now, I tested all this tonight and suffice to say, I didn't set my cycle times correctly, I need to make my logic a bit smarter and smoother.  I have a suspicion that I'm unintentionally designing a PID controller, but for now I'll start simple and get more complicated as necessary. 
    Auber has an example schematic wiring schematic in the user guide that gives you P / I / D settings as well as the duty cycle setting for their PID controllers for a smoker.  I have been using the settings in my system, and it will lock the temperature to within 1 degree.  I have cooked at 225, 250 and 350 with the sytem, and it is amazing how close it can hold the temperature.  You may want to check it out before you make your own algorithm.
  • pezking7ppezking7p Posts: 132


    Auber has an example schematic wiring schematic in the user guide that gives you P / I / D settings as well as the duty cycle setting for their PID controllers for a smoker.  I have been using the settings in my system, and it will lock the temperature to within 1 degree.  I have cooked at 225, 250 and 350 with the sytem, and it is amazing how close it can hold the temperature.  You may want to check it out before you make your own algorithm.
    Thanks for that info Mr. tgkle. 

    I did some reading/thinking last night, and some more just now on Auber's website.  I've decided to change my temp control strategy and use a simple P control (the P from PID), because the response of the egg is so slow.  More like a glorified thermostat. 

    I'm also changing the time scales over which I make changes.  Last night I was using 10s and 1 minute intervals.  I'll go to more like 10 minutes and 2 minutes I think.  10 minutes to determine what the set point *should* be, and 2 minutes to determine what is the current error. 
  • Here is my inspiration:



    The schematic is pretty simple

    image



    The logic is pretty easy to follow:

    I finally took the plunge and bought my large Big Green Easter Egg from Roswell Hardware in Roswell, GA 03/31/2012
  • pezking7ppezking7p Posts: 132
    The circuitry is certainly very simple when you use thermistor probes.  It's also very simple when you use a serial LCD instead of an LED set up like I've done.  I'd like to upgrade to the LCD eventually for better display, but they're pretty pricy and I'm cheap :)

    Looking at the PID code they used....I'm going to review that some more later, and I'll probably just implement it.  Because I want to move on to other parts of this project.  Thanks a lot for posting this. 
  • pezking7ppezking7p Posts: 132
    edited April 2012
    OK, here are vids as promised from last night and tonight.  The vids are boring and uncut (sorry).  Basically, the thing works after much finagling, holds temp for at least 2 hours.  I still need to add buttons, a second temp probe, and put it in a box.  Thoughts for other features to add? 

    Ready for a leg of lamb this weekend!

  • ChubbsChubbs Posts: 6,692
    Impressive.
    Columbia, SC --- LBGE 2011 -- MINI BGE 2013
  • spotco2spotco2 Posts: 61
    That's awesome!
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