November 2005, Issue 184

Large-Scale Electronic Display

DISPLAY DIGITS

Most amateur cricket games are played in the daytime. To save power, reduce complexity, and keep costs down, I used electromechanical digits instead of LEDs. All the data is numeric. If cost isn’t a factor for you, you could include alphanumeric characters. Just remember that segment control complexity will increase and a typical single character will cost three times as much as a seven-segment digit.

My display’s seven-segment format has been adequate for my needs. The digits require power only when they’re updating. This power-saving feature is one of the system’s best characteristics.

Digits are available in sizes ranging from 2.25" to 18" high. Digit sizes correlate to viewing distances. A 1" digit is recommended if people will be viewing your board from distances closer than 40¢ away.

Digits are available in red, white, and yellow. The latter is at the peak of the visible spectrum. I chose this color because I was planning to use my scoreboard outdoors.

A digit consists of seven separate electromagnetic-operated segments designed to be mechanically bistable. In one position, the segment vane shows no color (black). In the other position, the vane shows color (Saturn yellow). A digit requires a 12-VDC pulse applied to a coil (located behind a vane) to rotate the vane from one color to the other. Coils are center-tapped. The durations of pulses vary with digit sizes. Figure 1 shows a digit vane and coil arrangement together with steering and protection diodes.