Modernizing a Vintage Police Cruiser Data Terminal with a BeagleBone
I’m sure you’re a fine, upstanding citizen who has never had to spend any time in the back of a police cruiser. But, if you had—or if you’re a police officer yourself, or just saw COPS—you would have noticed that most cruisers are outfitted with a computer.
These days, that’ll probably be something like a Panasonic Toughbook. In the ’80s and early ’90s, however, there is a good chance that would have been the Motorolla MDT-9100.
Recently, several MDT-9100 data terminals popped up on eBay, and Trammell Hudson and other members of the NYC Resistor hackerspace were able to snag a few. After experimenting with the terminal as it was—Windows 3.1 greatness and all—Trammell set out to upgrade his MDT with a BeagleBone.
He wanted to retain the original aesthetics, including the monochrome CRT monitor, so the big challenge was reverse-engineering the old hardware connections.
Trammell connected the BeagleBone to the MDT’s 16x2 header with a BBB Prototyping Cape board. But, as you’d expect, that wasn’t exactly plug-and-play. After some probing with an oscilloscope, he was able to deduce that the monitor was using a fairly standard VGA signal of 640 x 480 at 60 Hz with a pixel frequency of 25.175. Getting the Beagle Bone to correctly output that signal took some hacking, but eventually he had working video on the monitor.
The keyboard connection was more straightforward, and used a matrix layout that’s similar to just about every other keyboard ever made. With the keyboard and monitor working, the Beagle Bone could be used to run Linux as expected.
Of course, the monochrome monitor reduces usability, at least by modern standards, but it definitely looks great.