Temperature Controled Charcoal Smoker
Use an Arduino MKR1000 to maintain a constant temperature in a charcoal smoker and allow monitoring over Wifi,
Most serious BBQ smokers know that the best flavor comes from using charcoal to heat their smokers. Propane and electric smokers have better temperature control, but lose that charcoal flavor. As a heat source, charcoal can be a pain. You need to constantly monitor the temperature, adjust the vents to try to get the right temperature, and have to play with it a few times to get it just right. Then, you’ve got to keep doing that every half hour as the charcoal level changes in the smoker. Wouldn’t it be great to just sit back on your couch, enjoying your favorite cold beverage and sporting event on the TV while letting the smoker do its thing?
Create a controller that monitors the temperature in the smoker and adjusts the airflow to the charcoal to maintain the correct temperature. Also, provide a way to monitor the temperatures of both the smoker and meat probes remotely. This is based on the soon to be released Arduino MKR1000 with built in Wi-Fi and support for charging a LiPo battery.
The temperature in the smoke is monitored using a 100K NTC Thermistor in a voltage divider connected to one of the analog inputs of the MKR. This thermistor was chosen as it is used for Prusa RepRab hot ends in 3D printers, so they are widely available and inexpensive. The can be bought already soldered to high temperature silicon insulated wire to make the ideal temperature probe. The thermistor is inserted in a length thin (1/4 inch or smaller) stainless steel tube for physical protection with one end crimped off to close it and the wires secured at the other end using heat shrink.
The voltage divider uses a 10K resister as the other half of the voltage divider. This value was chosen as it is close to the resistance of the 100K NTC thermistor at typical smoker temperatures (225 F). This gives a good range for temperature measurement, providing readings from about 50 F to over 300 F with reasonable granularity.
A0 is used to monitor the temperature. It uses a shorter probe that is placed on the grate inside the smoker. The other analog pins can be used to create more thermistor probes and voltage dividers to be inserted into the meat being smoked to monitor the internal temperature of the meat to know when it is cooked.
On the other side, a small blower is attached to the vent on the smoker. A small stainless steel dog food dish is attached over the vent on the smoker and the blower is attached to hole in the bottom of the dish. This serves two functions, first to completely cover the air vent, and secondly to provide some thermal isolation between the body of the smoker and the blower. The blower is controlled using a N channel MOSFET. This could be directly wired, but for ease of construction, a MOSFET model was used. The gate on the MOSFET is connected to the Arduino’s digital pin
For the first implementation, everything is done on a breadboard to keep things simple. The thermistor bridge(s) are easy to wire, the 10K resistor from Vcc (3.3V for the MKR) to one side of the thermistor and the other side goes to ground. Connect a jumper between the center of the bridge and an analog pin on the MKR. Cut a length of tubing to use for the probe, Crimp one end in a vice to seal it. Pliers are then used to fold the corners of the crimped tubing to make a sharper point. slide the thermistor in the tubing till it reaches the end. Slip a piece of shrink wrap over the other end and wires. Apply heat to shrink it down and secure the wires.
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