|Home-brew Ethernet to RS-232 converter
For a recent party, I was looking for a better solution to my current audio setup and happened across a reconditioned Apple Airport Express on the web. While it has many features, I primarily wanted it for streaming music via iTunes on the ol laptop to my stereo receiver over the home network. With WiFi enabled I can locate the computer anywhere in the house I want. And I can control the playlist with the remote app on my iPhone. Got it, hooked it up, and everything worked great... but something was missing.
For the same party, I was planning to set up my Betabrite scrolling LED sign to display a few generic messages such as the contents of the kegerator and a couple birthday wishes. I quickly realized how boring the repetition would be. You really must have continual content updates to keep the public's attention. Hmmm, maybe I should heed my own advice with this blog ;) I've seen other people scroll twitter updates and directed text messages to their betabrites but I don't currently have their programming chops so I opted to gobble up some local data.
I thought I would be neat to combo the new sound system with the display and scroll the currently playing song title and artist on the betabrite. I had two weeks before the party, plenty of time right? There were challenges.
Challenge number one, hardware. In a nutshell, I needed an Ethernet to serial (RS-232) converter so I could connect the Betabrite directly to my router. You can buy a quality unit for around a hundred dollars but a quick trip to the spare parts bin yielded a bounty that would get me most of the way there. The heavy lifting is done with a Lantronix XPORT Embedded Ethernet Device Server. I'm a big fan of these little guys. It has many features but for this project I only utilized its UART (serial) output. On the PC side, you can use vendor provided software to create a virtual com port eliminating the need to fool with setting up a socket connection. The XPORT outputs TTL level signals but the betabrite sign requires +/-15V (RS-232) so I needed to gin up a proto board with a level shifter on it. As luck would have it, I made such a board for a previous project. After tossing in a 3.3V linear regulator to power the XPORT, the hardware was complete.
Challenge number two, software. This was by no means trivial, I dabble in the medium at best. From a past project I already had a little C++ code that talks to the serial port so I decided to start there. The next logical steps were to gather up relevant information from iTunes, format said info, and write it out to the Betabrite. On a Mac, interacting with iTunes is native but Windows plays with iTunes a little differently. It uses the COM object interface to handle the data exchange. Thank goodness for Google and online example code. The only real trick was setting up the Visual C++ dependencies correctly and getting all the various updates and whatnot working. Looking through forums for semi-useful and somewhat relevant information is tedious. I'll provide the code and environment setup instructions upon request. Writing to the Betabrite also proved to be a bit tricky. I had the programming guide along with some sample scripts but I still had to snoop the serial data from the vendor software to figure out the ins and outs of the protocol. You can never underestimate the importance of a good technical writer.
Having the Betabrite display update with the currently playing song turned out to be a hit with the party goers. I'll have to make it permanent fixture for future gatherings. Maybe I can even get some tweets up there next time.