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.