Digs for QPID

After many months of thinking about the design, I finally started putting together a housing for QPID. Since it'll be sitting outside all day, it needs to be pretty weather-proof so water resistance and wind resistance are crucial. And the connectors need to be easily accessible but protected from the elements.

I built a basic stand out of black iron pipe. It's cheap, flexible (in terms of design), and it seems to go well with the BBQ smoker aesthetic. And the weight will help to ensure QPID stays put despite wind gusts and rambunctious beagles. The design is also stable when the unit is laid on its back, with makes hooking up the connectors underneath breeze.

The housing itself is made from 1/2" poplar. This part is still a work in progress, and I'll be adding additional panels on the top and side to shield things from the elements. Once everything's done I'll paint/seal it with a textured metallic paint to keep with the overall look.

For the LEDs, I may cover the front with a thin sheet of clear plastic and leave the indicators unpainted or maybe white. The other option is to find some clear plastic plugs or dowels and secure them in the holes with a waterproof sealant.

Arduino Shield Layout

In case anyone out there needs it (you know who you are), here's the basic layout file for ExpressPCB that I created to make the QPID shield. The pins are labeled and positioned to precisely match the Arduino Duemilanove and AsyncLabs' new BlackWidow. Hopefully this will come in handy if you're looking to create a custom shield using the ExpressPCB software.

QPID Shield Hardware Specs

In response to a number of requests I've received during the last few months, I've posted full specs for the QPID Shield. This PDF includes PCB artwork, component locations, and a detailed parts list. The design is provided under the terms of the TAPR Noncommercial Hardware License.

If you print the document, make sure the 'no scaling' option is selected to ensure that the PCB artwork is printed exactly to scale. Everything's been double checked for accuracy and completeness, but please post a comment below if you encounter any discrepancies or have any questions.

With a major winter storm approaching Chicago this evening, it's hard to imagine that we'll be smoking meat again in a few short months...

Enjoy!

QPID Software Is Now Open Source!

I've had several requests for the QPID source code and finally had some time to clean things up a bit and set up a code repository. So in case you're curious how QPID works or could borrow a code snippet for your own Arduino project, you can now access the source code on GitHub. Note that this repository only contains the QPID-specific code; the WiServer code is hosted separately in the Async Labs repo.

Time To Kick Things Up A Notch

Other than the lack of a real enclosure, I'm pretty satisfied with QPID at this point. It does everything I originally wanted it do, and it makes hours and hours of smoking at a precise temperature an easy, hassle free activity. Perhaps it's time to take things to a whole new level...

One of the longest-running debates in the history of food is the correct smoker temperature to use. Some people go with 225 for ribs, others say 250, while some think 200 is best. I think it's time for a little science and technology to turn this debate on its head.

I came across this very interesting (and very technical) article about sous vide cooking, which is French for 'in a vacuum'. The food is sealed in plastic in a vacuum and then slowly cooked in a water bath at a low temperature for a long period of time (sound familiar?). The article does a great job of explaining how heat affects the meat and why holding a lower temperature results in a more tender meat. The key to the whole process is keeping the temperature of the food within a precise temperature range... something that QPID could potentially do!

Sous vide employs water baths to heat the food; the higher specific heat of water allows for rapid heating of the food, and the food temperature will then mirror that of the water bath so maintaining the temperature is quite easy. I'm not about to dunk ribs in a vat of hot water, but I think the way in which the water heats the food can be approximated with some clever software.

Instead of setting the temperature of the smoker, QPID could be configured to quickly reach and hold a specific meat temperature. So perhaps the smoker would start out at 225 initially, but would then scale back to a lower temperature to keep the meat at just the right point. The hardware is already there to do this, all that's required is a little programming.

Log Data

With QPID's control algorithm now running quite nicely, I logged data during a recent rib smoking to see just how good it is. Weather conditions were cool and windy, so it was a good test for the system.

The plot shows that the actual temperature (red) stays within 2 degrees of the target temperature (blue), which is way better than I could ever hope to do adjusting the dampers by hand. The green line shows how the fan speed adjusts to maintain the desired temperature.

The yellow line shows the average fan utilization gradually increasing as the fuel is consumed. The QPID software monitors this value and sends an alert when it exceeds a preset threshold. Since I'd like a little advanced warning, I think 70% would be a good value.

Twitter Kinda Sucks

At first I was thrilled about the prospect of using Twitter to send updates. It's free, it's easy to send updates via an HTTP POST, and it handles all of the configuration for devices and following options. But there's a catch. It's really unreliable. :-(

During the course of my testing, I've noticed that I get SMS messages about 50-60% of the time, and if the message is an urgent alert about the smoker needing attention, that's just not acceptable. So, perhaps I need to add an SMTP feature to WiServer and go straight to my carrier's gateway server instead...

On the plus side, I have greatly improved the control algorithm. It makes better use of temperate changes over time to control the fan, and it also has the capability to sense when the smoker's been opened (thus avoiding false alarms for a low fire).