(This post is entirely on the hardware side of things so if you only care about my software ramblings, these are not the droids you are looking for.)
Since physical computing is an area I really have no deep background in, as with most of my projects that involve it, I owe quite a bit of credit to others. Here are most if not all of the sources I used:
- Adafruit (support them, they rock! and they accept bitcoin!)
- General Stuff
- Xively Stuff
The build started like any self respecting build would…. as a prototype in a fishing tackle box!
Surprisingly enough, once the kinks were worked out this worked pretty darn well. Believe it or not, I cooked about 5 meals like this. A fire extinguisher was near by.
The prototype consisted of:
- Very awesome cheap tackle box
- Raspberry Pi rev B
- Pi Cobbler
- GFCI receptacle (standard 120v)
- Solid State Relay (SSR)
- 1Wire Temperature Sensor DS18B20
Now that I’m writing this ex post facto, the high voltage bits are WAY FREAKING overkill for this implementation with my current slow cooker. (25A SSR?!? I think the later bits I added are bout 10A capable…) See the last post on electricity usage for more on that. What’s good is, assuming I didn’t make any huge errors (which may be a leap) I’ll be able to use this with much more powerful heating elements like a heat stick to brew beer…. we’ll see…..
*I’ll post a wiring diagram here* from EAGLE once I figure it out. It’s not the most intuitive application.
Now this prototype worked great, but I wanted some bling. I’ve never built anything with much bling to date so this was quite the learning experience. Via the Awesomeness that is Adafruit, I found the 7 Segment display. I’m in love:
I scrapped my first idea of just using a LCD text display, and went with two of these days. Partly this decision was because I was having stability issues with the LCD i first tested with gibberish eventually always showing up, but also because I don’t need to display much text at all. I wanted to keep this build purpose built and not add bells and whistles (like speakers and pandora functions like I originally spec’ed!). So target temp, current temp and some sort of status indicators is all I need. I wanted to include some timer displays to help with the cooking process but the lack of a real time clock in the rPi gave me some headache so I scrapped that idea. Maybe i’ll revisit with either the add on board or a beagle bone.
I ordered a number of bits up from Adafruit and Digikey. Found a case at the hardware store (which probably was a mistake….need to do more research on cases next time…). And dove in… Slowly I started adding bits. First a 7segment LCD:
I read somewhere it really helps when cutting cases to use painters tape on top to draw your lines and keep the edges clean. Yeah i doubt that helped my absolute hack job:
Progress was made pretty quickly, as I started getting time pressure to move on to other projects.
And started cutting the ports for the power in & out:
And there she is. Fully working and how she looks today (with a slightly corrected label that someone on Facebook wouldn’t let go). Notice all the empty space on the bottom half which may some day be used for some timer displays.
And on her maiden voyage, she cooked us up quite possibly the most tasty meal yet. Tenderloin Steaks with Morel Cream. As Ferris Bueller said, “If you have the means, I highly recommend picking one up.”
And here she is, mostly finished (TM).
Parts added for the final build:
- Some silly case from Lowe’s
- 2 x 7 Segment LCD, Adafruit
- Panel Mount USB Cable – B Female to Micro-B Male, Adafruit (not shown in photos)
- 5mm LED Holder, Sparkfun
- 5mm Green and Red LED, Sparkfun
- Power in port, Digikey (not shown in photos)
- Power out receptacle, Digikey (not shown in photos)
- Terminal blocks for 120v (25A!!)
If I was to continue development on this, the items on my list are:
- Add timers
- Add audible alerts
- Add on/off switch
- Add detachable temperature probe
- Better case
- Currently the rPI uses power from an external USB source due to lack of space for the transformer within the case. This should be wired in.
There you have it. Now I don’t really need feedback on everything I did wrong here. No I don’t have a fuse wired into the box, I’m relying on the GCFI that I plug into, etc.. This is more or less a proof of concept that is sticking a round a while. If I keep using it, as it seems like I am, I really am considering going legit with one of these store bought monsters.