Hacking LED Signs ----------------- (Spring, 1997) By Bernie S. We've all seen them - those annoying, attention-getting LED signs with moving, flashing messages. They're in airports, train stations, bus terminals, vending machines, retail establishments, banks, and even government offices. Almost without exception, they're in high-traffic areas where lots of people are subjected to their not-sointeresting messages. This article provides a brief overview of most types of displays out there, how they're programmed, and how you can use them to get your message out to the people. In no way should this article be misconstrued as encouraging unauthorized programming of such signs, for that would be in violation of State and Federal laws and punishable by up to 10 years in prison. No matter how harmless the method may seem, expressing yourself in ways our government doesn't approve of can be hazardous to your health. (Maybe all electronic hardware and software should have government warning labels similar to cigarettes and alcohol.) In any case, be forewarned. Most LED signs out there are self-contained, microprocessor-based units that are field-programmable by a variety of methods depending on the manufacturer, model, and configuration. These methods include direct RS-232 connection, telephone modem, proprietary or PC keyboard connection, wireless telemetry (via cellular modem, packet radio, ARDIS or RAM radio data networks, FM broadcast via SCA or RDS, or Motorola paging data receiver), and wireless infrared keyboard programming. Older "dumb" LED signs require constant connection to a proprietary or PC-based data source, which stores messaging data in addition to controlling the LED display. All use multiplexed Light Emitting Diode arrays, from tiny one-line units only a few inches long to massive 16x40 foot models. Large dynamic text displays using arrays of incandescent bulbs or electromechanical flippers painted fluorescent green and illuminated by black light are often placed alongside highways or on overpasses to inform automobile travelers of road and traffic conditions. Portable programmable road signs are often mounted on wheels atop a small trailer (complete with gasoline generator and a dedicated PC or proprietary controller or cellular modem) and towed to road construction sites as needed. Surprisingly, the metal cabinet containing the programming electronics is seldom (or insecurely) locked. Large LED array signs are often used on factory floors to display production run data to assembly-line workers, or in call centers to indicate call volume, ANI data, or other information to operators. These units are usually hardwired via RS-232 interface to a company computer. If you come across a programmable sign (say, at a garage sale but there is no manual or programming device with it) get the manufacturer's name off the unit and contact them for an operations and programming manual for that model. Often, you can get it free if the company believes you're a previous customer. Also request a catalog of accessories for that model; it will be helpful in determining specifically what additional hardware you'll need to program and power it. There are so many manufacturers, models, and programming interfaces out there that it's not always obvious how to go about it without proper documentation or social-engineering one of the manufacturer's technicians. Once you have the sign plugged in and operating (they're usually powered by an AC adapter, which is filtered and regulated on the sign's main circuit board), you can experiment with programming various messages. Some models are fairly intelligent and allow for multiple and scheduled messages, and special effects like rotation, scrolling, zooming, bitmapped graphics, and multiple colors (using rapidly switched red and green diodes at various duty cycles). Blue LEDs are still too expensive to use in volume, which is why you don't see any blue or truecolor LED signs yet. When blue LEDs are cheap, all primary color requirements will be met and any color in the spectrum will be easy to generate, like the color cathoderay tubes in TVs and computer monitors do. Eventually, giant full-color LED video billboards will be commonplace. The author has heard of several humorous situations involving LED signs programmed by unauthorized parties. In one case, a state-owned lottery ticket vending machine with an LED sign mounted on it was located in a drugstore. It had apparently been reprogrammed from the street through the drugstore's main window using an infrared keypad to say, "This machine sells only losing tickets - don't waste your money on another government scam!" When this was called to the store manager's attention, he panicked and began wildly pushing all the vending machine's buttons in a futile effort to delete the message, eventually unplugging the entire machine (preventing it from vending tickets altogether). In another case, an LED sign on a prepaidphone-card vending machine in a major train station had been reprogrammed to say, "These phone cards are a total rip-off at 50 cents a minute!" The machine didn't indicate the true cost of the cards; a call to the vending company confirmed they were indeed 50 cents a minute, so some hacker arguably provided a valuable consumer advisory service. A bank's LED sign in their main window soliciting homeowner loans had been reprogrammed to say it was offering a special one-day sale on new hundred-dollar bills for only fifty dollars each (one per customer). There were some rather excited people lining up until a chagrined bank manager unplugged the sign. An observant reader wrote in to this issue's letters section to say he'd noticed a large LED sign by the escalators at New York's 53rd and Lexington subway station (by Citicorp Center where monthly 2600 hacker gatherings are held) had been reprogrammed to announce the time and dates of the hacker gatherings, inviting everyone to come. Previously, the sign merely advised people to watch their step on the escalator. Tens of thousands of people a day got to read that sign; that's real power. There must be thousands more LED signs out there just begging to be programmed with more interesting messages. Do any come to mind?