DIY temp controller


 
Originally posted by RobM (YankeeRob):
You have to trust the first therm for the real temp. Cheap kitchen and wireless temps will work for this. I can control a WSM or BGE with just a single pit therm that is accurate and manually adjusting the vents. Same thing but a tad bit smarter with auto drafting.

-rob
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Not to over simplify what you are trying to accomplish, and this is by means not the most efficient way to burn burn fuel, but have you explored the possibility of just using a thermostat style of control. Set a high and low. When the high is hit, shut off the fan. When the low is hit, turn the fan on. If you charted the temperatures, it would seesaw all night long. Again, not very efficient, but good enough for almost all household ovens, and very easy to setup.

My control system has 2 options for control. PID (with some fuzzy modifications) as explained above for very accurate control. But I also have, what I call, "bang bang" control, used mainly to control large electric smokers that tend to burn up rheostats due to the high wattage (and the cheap components that I use to regulate them)
 
Originally posted by Josh Greer:
Not to over simplify what you are trying to accomplish, and this is by means not the most efficient way to burn burn fuel, but have you explored the possibility of just using a thermostat style of control. Set a high and low. When the high is hit, shut off the fan. When the low is hit, turn the fan on. If you charted the temperatures, it would seesaw all night long. Again, not very efficient, but good enough for almost all household ovens, and very easy to setup.
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What you describe is the most common technique for filtering the feedback loop as to avoid oscillations.
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We call these set points "high watermark" and "low watermark" if you can follow the analogy. Same technique is used in buffer management in many applications and opperating systems.
 
http://www.circuitcellar.com/library/print/0503/moyer154/

Here is a circuit that does what you guys are talking about. I posted it a couple months ago on here and did not get as much discussion as this thread has.

It uses a cheap microprocessor that is programmed with the "curve" for the thermocouple response to determine the temperature. The target temperature is set via a variable resistor that basically just gives a variable voltage into the IC that gets compared to the voltage produced by the thermocouples.

The write up on the web site does a pretty good job of explaining how it all works.

Instead of using pulse width modulation for controlling the fan speed, he chose just to have the fan cycle on and off as needed to maintain the target temperature.

It also has provisions for sending a serial output for data logging or remote monitoring via a network.
 
Thanks Ken,

I did see this discussion while researching what other people have done. My idea though is to make a dummed down version without a uP. I know the problem can be easily solved with code but that brings up the expense. I'm thinking ~ $40 not including the fan. This is just a play project. I already have a Stoker and a Guru.

-rob
 
Originally posted by RobM (YankeeRob):
Thanks Ken,

I did see this discussion while researching what other people have done. My idea though is to make a dummed down version without a uP. I know the problem can be easily solved with code but that brings up the expense. I'm thinking ~ $40 not including the fan. This is just a play project. I already have a Stoker and a Guru.

-rob
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Already have 2 ATC systems and looking to build one?

Tell you what, I'll pitch in a send you some resistors and such in exchanage for one of your "old" systems.
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The new hack unit is just for backup. I got and built the $25 PWM linear circuit and attached the Guru fan. It runs normally at 18 and 12 volts. I still need to spec out the diff amp but that should be simple.


-rpb
 
The one thing I will add is that the frequency the fan runs at is most annoying as it is audible. Pretty sure though after a few beers I could ignore it.

-rob
 
And that is the downside of PWM controllers. They tend to make some motors noisy. This noise btw, is different than the mechanical noise the fan makes.
 
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