A Dungeons and Dragons dice tower is designed to randomize the dice more efficiently and decoratively over just hand throwing them on a table or inside a cardboard tray. While you can buy them just about any place where board games are sold, but more creative gamers prefer to build their own, which is what automation software engineer John Anderson did with his "Heathkit" D&D Digital Dice Tower.
Anderson constructed his tower around a 1975 Bell & Howell IMD-202 digital multimeter, which is outfitted with the original Nixie tube display, power supply, and case. To give it new functionality as a D&D dice tower, Anderson had to hand-wire an AVR-based controller board that is integrated into the original PCB. He also added a two-digit thumbwheel switch, an eight-way rotary switch, and a panel mount button. He even included a new D&D graphic to the faceplate to keep with the popular theme of the game.
The D&D Digital Dice Tower works by first selecting the number of dice needed for a roll using two digital thumbwheel switches, then the dice type (2/4/6/8/10/12/20/100-sided) using a rotary switch, and finally, pressing the roll button to display the result. Anderson explains, “The device applies the GNU AVR lib C pseudo random rand() function, calculates the result, and displays it on the nixie tube display. The user can then re-roll by pressing the roll button again, or change the count and/or dice and roll a different set of die. It's that simple to use.”
A complete walkthrough of the D&D Digital Dice Tower is available on Anderson's project page, complete with schematics and source code for those who would like to create their own. His design became popular with his gaming companions, so much so, that he started making updated versions for his friends with different features, which can be found here.