First steps to BBQ bliss (at least for me)

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.

In the picture, you might notice that the hose barb is plastic – that REALLY didn’t work out so well!  It has since been changed to a metal barb insulated with high temperature rubber tape – works great with plastic hose as the connection between fan and manifold.
I did a bunch of experimenting with the settings of the program, and got everything tuned up so that it keeps the temperature within 5 degrees F or so – more than close enough for my purposes.
Here’s a picture of the test-bed board I ended up with (some parts have been removed and are on the new version):
Image
After that, I decided that I needed it to be a little “classier”.  So I bought a license for one of the entry-level versions of DipTrace and designed a PCB that I had made by OSHPark.  Here’s that board:
pcb
I have since built up the board and it works great!  Next I’ll document the changes I made once I had the couple of mistakes I made on the PCB fixed.  How is it that I spent HOUR AFTER HOUR checking everything on the design, and it still had two mistakes?  They were both easily fixed in a couple of minutes, but still……….
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BBQ and electronics – a match made in heaven?

I’m just going to come out and say it – I LOVE BBQ!

To me, there;s nothing better than pulling that gorgeous pork shoulder from the smoker, shredding it, and creating FABULOUS pulled pork sandwiches with the result.  I have experimented for years and come up with some winners – and a lot of losers – along the way.  The losers are all part of the learning process.

I’ve used a couple of different smokers, and the most difficult thing about it is keeping the temperature where you want it.  It sometimes requires constant attention.

Last winter, I was wandering around the internet and came upon a link from Alton Brown’s blog (he my culinary hero) to the Pitmaster IQ temperature controller. In the Good Eats episode “Right On Q”, Mr. Brown used the temperature controller to keep his smoker at the perfect temperature to cook BBQ.

Here’s the episode on YouTube.  He starts talking about the temperature controller at around 36:48.

My thought on seeing this was: “I can make that!”  I’ve been making microcontroller projects as a hobby for years.

I did some more research (read: Google Searches) and found that there are DOZENS of these things, ranging in price from $150 to $500 units with LCD graphing displays, bluetooth and wireless control, and more!

After looking at features, I decided on the following requirements for my controller:

1) Capable of being powered from a power supply or battery.

2) LCD screen

3) Simple controls (many of the ones out there have lots of buttons and switches)

4) PID process control to maintain the temperature

5) PWM control of fan speed

6) Meat probe to monitor meat temperature

7) Serial (RS-232) port to be used for logging to PC, or communications with modules such as

Bluetooth or Wireless.

I then sat down and started to figure out what I needed to do to accomplish this.  I had never used an LCD display on a project before – so that was first.  Second was reading a thermocouple using an ADC port (never done that either).  Third was PWM control of a motor – I had controlled the brightness of LED’s before, but never a motor. I had also never created a microcontroller serial port before,

My path was set: next time I’ll talk about the experiments that led me to where I am now.