Finally starting my PID controller
I have all of the parts I need and am finally starting my PID temp controller build. My birthday is next month and I want to do a brisket, but don't want to be up all night again. I'll post pics tomorrow, but for now it should work as follows:
Temp control via a Thermaltake smartfan, high/low temp alarm (indoor and outdoor), A/C power fail alarm, meat temp reached alarm (if I can get the voltage divider circuit and OP amp working), lid open fan disconnect, PID shutdown when meat temp is reached.
I should have the whole thing running except for the indoor alarm and possibly the meat temp reached alarm and shutdown. I built an OP amp circuit today to boost the beeper voltage on my thermometer to a high enough voltage to trigger a delay timer relay that will power the alarm, but didn't get to test it yet. It should work, in theory. I also wanted to power the meat thermometer from the 12vdc power supply and avoid the batteries, but haven't got the voltage divider quite right. I need to drop the 12vdc to 3vdc for the thermometer.
If all goes well tomorrow, I should be good to go. If all goes poorly, I will get electrocuted or burn the house down in really spectacular fashion.
In the event of perfectly smoked meat, please post pics.
If the house is a towering inferno, I would like to see that as well.
I'll see what I can do in either event. Kind of hoping for the first option though.
During the build I decided to make this a prototype unit. I discovered a number of changes I want to make, but still wanted to get a functioning unit as soon as possible.
This is a shot of the A/C power fail relay. A/C power holds the relay energized keeping the normally closed contacts in the open position. Those contacts are wired to a 12vdc battery and a loud piezo buzzer. Should the A/C power go out, the contacts will close turning on the buzzer. Since my PID controller is 120vac, I thought this was an important feature:
For the fan housing, I chose a deep 4” weatherproof box. I cut out the lid to expose the blades then sandwiched the back of the project box (also cut out) between the fan box and the lid. The fan has a built in rheostat so I can control fan speed:
In the back of the fan box I drilled a 1” hole to accept a ¾” liquidtight connector. A length of liquidtight tubing will transfer the air to the UDS:
The front panel is started. When finished there will also be a “fan running” LED, the fan rheostat, and another switch or two. The three switches installed are “outdoor alarm disconnect”, “indoor alarm disconnect”, and “A/C power fail” disconnect. Additional switches will be used to manually disable the fan and meat temp alarm disconnect:
Here is the el-cheapo meat thermometer I am currently using. If I can make this work properly, I may invest in a more expensive unit:
I designed a voltage divider circuit to reduce the 12vdc from the power supply to just over 3vdc so I can run the thermometer without batteries. It appears to work:
Here are a couple of shots of the guts so far. The small circuit board in the lower right corner is a delay timer relay. It will be used to activate a much louder alarm than the meat thermometer has. I designed an OP amp circuit to take the very tiny voltage applied to the thermometers built in piezo sounder and boost it to 5vdc which is enough to activate the trigger on the delay relay. The relay will latch and turn on a very loud alarm:
And finally, the front panel powered up. Everything seems to work so far. I’m having a little trouble with the thermometer circuits. For some reason it keeps triggering the delay relay as soon as I connect it. I’ll review the circuits and see what went wrong. I also have not had a chance to experiment with the wireless doorbell I bought. I want to modify it to sound an indoor alarm if the PID set temp swings out of range (like if the UDS runs out of fuel…etc…).
For the rebuilt version, I plan to use a watertight NEMA enclosure with watertight fittings. Since I don’t take this drum anywhere, I want this to be permanent. I am also planning to replace the current 12vdc power supply with a different unit. The current one uses a 16vac power source, which requires the use of a plug-in transformer. I want a 120vac input to free up some space and make the entire unit fit into a single enclosure.
I’m sure there a number of details I have forgotten, but I’ll post everything up as it comes together.
Very cool. What is your budget for this project looking like?
I haven't really been keeping track. I had a lot of the stuff on hand. The PID controller was about $43, the thermocouple was $12 and the SSR $7. I pretty much had the rest of it. So I guess a basic system would run about $80 or so. Designing and building it is half the fun. Being able to customize it any way I want is a plus too.
How was the brisket?
Haven't used it on a brisket yet. The initial runs have revealed a flaw in the air supply. It appears that 3/4" liquidtite is not large enough. I am modifying the air supply to 1-1/2". I'll post back when I have more data.
Cool project bro!! Can't wait to see the final result.
Did this ever get finished? How did it work
Just my 2¢ Mike :thumbup:
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