So I had to learn a few things……..
First I started with ProtoBoard and added a microcontroller (PIC 16F886) and a two line by 16 character LCD.
I wrote a program that displayed text on the LCD – step one was complete. I then added an IRF630 MOSFET as a speed controller and learned how to control the speed of a fan – step two.
The next learning step was a little tougher – I had never worked with any analog to digital sampling before. Thermocouples work by generating a voltage in relation to the temperature of the junction. The only problem is that its only 44 microvolts per degree celcius (for the K-type thermocouples I was using). This is a very small voltage to sample, so an OP-Amp is needed to boost the level to something more easily measurable. In addition, the junction that you measure the voltage at causes issues too – its another junction.
The answer? The Analog Devices AD595 – a ready-made thermocouple interface that outputs 10 millivolts per degree celcius, compensates for the measurement junction, and even has an alarm output that signals if a thermocouple fails! Perfect!
Using the AD595’s made my first analog-to-digital attempts easy.
I spent a couple of weeks writing software to read the thermocouple inside the smoker and control to speed of a 12VDC fan to reulate the temperature. I also added alarm points and monitoring of the meat temperature through another thermocouple.
Now that I had a way to control it – I needed a fan. I mounted a computer fan in the side of a Rubbermaid container, put a plate to seal the fan in and mounted a 1 1/4″ hose barb to let the air out. I unbolted the damper from my smoker, and mounted a stainless steel bowl with a hose barb. See the below picture for an idea of what I mean.