Operation KEG Part 3: Bespoke Kegbot

FormalKegbot

The Venture Café Kegerator Enhancement Group (VC-KEG) has been hard at work fulfilling its lofty mission to transform our kegerator into a technological marvel. As outlined in Operation KEG Part 2: Kegbot 101 the Kegbot open source beer kegerator control system has many virtues—most notably, the ability to measure keg temperature and beer consumption and to authenticate drinkers. Never satisfied to rest on his laurels though, Mr. Kegbot decided to take a trip to Savile Row and get himself a custom-made suit, hence the title of this post. Only the best for Venture Café! [Given that I have the artistic ability of a gnat, I commissioned my friend Ashley Short to render his new look in Photoshop.]

Why bother with the formal wear? For aesthetic reasons, of course. It’s perfectly understandable why the specifications for the Kegbot electronics call for old-school LEDs, resistors, capacitors, temperature sensors, and transistors with long wire leads. This choice of form factor makes self-assembly by hobbyists far easier. However, I just couldn’t get over the shocking resemblance of the Kegbot printed circuit boards (PCBs) to my 8th grade science project. I opted to redesign the PCBs with surface mount components, ensuring end products with sleeker, more sophisticated lines.

kegbot_controller

In a standard Kegbot build, an Arduino Uno acts as the primary controller. Arduino has done a great service to the world by bringing embedded computing to the masses. Arduinos are, for instance, immensely popular with hipsters creating ironic conceptual art installations that involve blinking LEDs. However, an Atmel Atmega328 8-bit microcontroller clocked at 16 MHz with no operating system has its limitations, prematurely thwarting VC-KEG’s Machiavellian scheme to rule the universe (of kegerators).

I considered two replacement options for the Arduino, both equipped with 32-bit ARM processors, the Raspberry Pi and the BeagleBone. Exhaustive feature comparisons live elsewhere on the Internet. The Raspberry Pi and required accessories retail for about ⅔ price of the $89 BeagleBone. The CPUs on both boards are clocked at upwards of 700 MHz, but the BeagleBone’s Texas Instruments AM335x ARM Cortex-A8 processor seriously outguns the Broadcom BCM2835 ARM11 on the Raspberry Pi.

BB-BONE-000beagle-hd-logo

Macho man microprocessor comparisons aside, the 65 externally accessible GPIO (General Purpose Input/Output) pins on the BeagleBone, make the Dog (woof!) the clear winner for the Venture Café Kegbot. The Raspberry Pi has a mere 8 GPIO pins, not enough to meet Kegbot requirements. (Ironically, Texas Instruments is one of my employer’s biggest competitors. But Analog Devices has no skin in this particular game, so as Robin Coxe, Venture Café bartender, I chose TI.)

The GPIO header connectors running along the edges of the BeagleBone enable the Kegbot Controller board to readily interface with the CPU. Mezzanine cards that mate with the BeagleBone to provide supplementary functionality such as the Kegbot Controller are called capes, in homage to the cape-wearing superhero beagle Underdog. Kegbot Controller inputs include temperature and flow readings from the Kegbot Coaster boards inside the kegerator. The processor can, in turn, activate relays, switch the LEDs on and off, and activate the buzzer over output lines. The BeagleBone sources 5V and 3.3 V DC power to the Controller board over the header connectors. Because the end result of my redesign of the Kegbot Controller to make it BeagleBone-compatible makes the entire get-up look like a flying squirrel, the Venture Café Kegboat Controller board shall henceforth be referred to as the BeagleBeer Flying Squirrel Controller.

As a self-respecting, card-carrying member of the Open Source Hardware Association, I forked the kegboard repository and uploaded the Venture Café Kegbot PCB design files and the Bill of Materials (BOM) to Github. I ordered the components on the BOM from Digikey, the mail-order electronics superstore in Thief River Falls, MN [of all places], and Sparkfun Electronics in Boulder, CO. [For those interested in building a standard Kegbot from scratch, click here and here for comprehensive parts lists.] I used Cadsoft Eagle PCB design software, originally developed in Germany, which has become the de facto standard for open source hardware designs. The arcane details of PCB design would probably bore most of you silly, but for those interested in learning more, the helpful engineers at Sparkfun have put together an excellent set of web tutorials on schematic capture, PCB layout , and parts creation using Eagle. The final PCB layouts of the Kegbot Coaster board and the BeagleBeer Flying Squirrel as rendered in the Eagle PCB layout tool:

VC_kegbot_coaster_layout

beaglebeer_controller

I plan to retrieve the hand-assembled PCBs from the contract manufacturer, Proxy Manufacturing in Methuen, MA, by the end of the week. Just like our beer, Venture Café electronics are locally sourced and artisanal. (“Wicked awesome!” as we Massholes liked to say back in the ‘80s.) The PCBs were fabricated in the Oregon, so the bespoke Venture Café Kegbot electronics can wear the “Made in the USA” label with pride. As soon as I have fully populated boards in hand, I’ll port the Kegbot controller code (written in C++) from the Arduino to the BeagleBone, a process that, like most things in life, is easier said than done. Fasten your seatbelts! In Operation KEG Part 4, I’ll document the fascinating saga of commissioning the Kegboard Coaster and the BeagleBeer Controller electronics.

coaster_pcbbeaglebeer_pcb

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