Thanks everybody for sending me your Monulator thoughts. I've meditated deeply upon them. Here's what I'm thinking now (more comments welcome!):
Many commenters say a case isn't essential. I'm convinced this is biased by many of my commenters being Chronulator customers, which are definitely a DIY breed. :-) I'm certain there's a class of users who would rather design their own case, or mount a bunch of bare Monulators in a rack in a server room. But that's a relatively small group of people. So I'm still investigating a case. Here's a sketch of what I'm thinking, from a mechanical standpoint:
I hope to employ a common manufacturing trick – keeping the cost of injection molding down by creating only one, symmetrical part. Two of these parts would fit together to produce the complete case.
The plastic will be translucent so that the RGB LED lights up the case from within. That should look super-cool…
I read a Wired article about hardware projects on Kickstarter, and how milled aluminum is de rigueur among Kickstarter projects, and isn't much more expensive than injection molding, at least for small volumes. I do dig aluminum. But aluminum doesn't allow for a nice rosy RGB LED glow through the case… So maybe for my next project.
The Monulator must get data from somewhere. The simple and cheap solution is to send data via USB, so that's how I designed it. But USB isn't ideal. You'll need to have a PC running all the time, fetching data from a sensor or the Internet, and passing it to your Monulator. The obvious solution is to support some form of wireless. But cheap wireless (like ZigBee or proprietary wireless chipsets) still needs a computer and compatible wireless dongle at the other end to fetch the data. A Wi-Fi device would be great, but they're expensive and power hungry, and would require a LOT of code on the microcontroller to implement TCP/IP and HTTP and parsing of the data source. But it turns out I was totally wrong about Wi-Fi…
Wishi, who I met via the HackRF project, prodded me to think again about wireless. We Tweeted back and forth about Digi XBees, which I thought only implemented ZigBee or custom wireless protocols. It turns out they also offer Wi-Fi modules, in the same popular XBee footprint, and for the surprisingly reasonable price of $35 US. With a Wi-Fi module, the Monulator could sit anywhere in your house or office and show you fresh data all day and night, regardless of where your PC or laptop is.
Of course, incorporating a $35 Wi-Fi module as a standard feature would dramatically increase the selling price of the Monulator. In fact, I was hoping to sell the Monulator for $35… So instead, I'm redesigning the circuit board to accept an XBee module, and you, the customer can buy the module and solder it in if you want. I might also offer a Kickstarter upgrade where I'd solder the extra Wi-Fi components for you.
A few commenters pointed out Web sites and monitoring software that would be great to interface to a Monulator: Cosm and StatsD / Graphite. I have yet to look into them, but it'd be great to have lots of sources for interesting data.
I bought a few of wireless modules – a few Digi XBees (ZigBee and Wi-Fi), and an XBee-footprint-compatible Wi-Fi module from Roving Networks. Last night, I hacked around a bit with the Roving Networks module (which has some HTTP support) and got it to download the latest Facebook stock price from Yahoo! Finance. I also got it to download the time until the next bus stops outside our house, which should be handy for my wife…
In addition to the wireless modifications I mentioned above, I'm revising the circuit board to work better with a case. I've enlarged the circuit board so that it can rest against flanges in the case, which would provide support for inserting and removing the USB cable. The circuit board might also provide some structure to the case. If I leave the back of the case wide open (exposing the circuit board), the circuit board could act as a light baffle for keeping the LED light from leaking out.
I've switched the USB connector from a mini-B to a full-size type B connector. Yes, that's the same chunky cable you see on the back of printers and most USB hubs. Considering how the circuit board needs to mate with the back of the meter, all other USB connector styles would require the connector to come out the side of the Monulator's case. I don't like that, because it'll look ugly and prevent you from stacking several Monulators side-by-side. So the USB cable will go into the back.
A bunch of my initial prototype work is now posted to a new GitHub repository, so have a look. And if you have new ideas or comments, please share them!