A decade ago I built a clock. It's a great clock, it uses a Beta Brite LED sign with a Python program running on a laptop with RS-232 interface to provide NTP-synchronized time, outside temperature read from the Internet, and the ability to telnet to a TCP/IP port and display custom messages.

It's been running quite nicely since I put the OS on flash after the last hard drive died. It's running on an ancient Thinkpad (so ancient that it has an on-board RS-232 port :-), and while it works quite well, it seems like a waste to be using all this space and power to run the sign.

Things like those wall-wart Linux systems got me to thinking about replacing the Thinkpad with a smaller, lower-power device. Read on for more information about what solutions I've found.

My first thought was using some small computer like a Gumstix or Beagle Board. However, I'd need something with Ethernet or more ideally WiFi, and these almost certainly have a fairly high learning curve as far as getting Linux loaded (into their tiny 128MB or so of RAM and flash), and getting all the software parts together to do what I need.

Early this morning I came up with the idea of: There's got to be an Ethernet to RS-232 device. And indeed I found some rather nice looking ones that were only $80. They also had a WiFi model, but the pricing on that one started getting up towards $200, and the hardware was fairly large. I found these by searching google for "ethernet serial".

These are basically little boxes that are 1-port serial "terminal servers". They also come in 2, 4, 8, and 16 port models. These might be very nice for use in a server space to connect to serial console ports of equipment, without having to find space for a larger terminal server like a port-master, or running serial cables between cabinets.

Then I wondered if the XBee modules included serial lines. And they do... These are little modules you can get from SparkFun and other places, which can do wireless mesh using a custom protocol and are extremely low power. They're neat board that include several analog and digital I/O lines as well as serial TX and RX. They look extremely neat.

But, the XBee modules serial is TTL level, so you need to put in a circuit to be able to drive a regular computer or Beta Brite serial port. Parts are available to convert these, but then I start needing to experiment to put together all these parts and power and all to make it work.

Having fairly limited time, I am very aware that the more complex the project is, the less likely I am to complete it.

I was getting ready to order a bunch of parts for doing the XBee setup, when I came across the WiFly module by Roving Networks. This is a small circuit board with a WiFi interface, and a TCP/IP stack so that you can send/receive data via either TCP or UDP to it's on-board serial and I/O ports.

The price is marginally higher than the XBee "Pro" modules once you add the parts needed for the "base station", the serial level converters, etc... All in a nearly self-contained module for $70.

Now, for our data-center I'd probably want to use wired Ethernet for reliability and RF noise reasons. But for my house, I think this is going to be a perfect solution.
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