Control the giant ex-British Rail platform clock 7-segment displays that are now available on the surplus market.

Recently, Dave Fisher of Display Electronics told EPE that he had acquired several thousand electro-mechanical "big digits". These had previously graced the platforms of British Rail as 6-digit 7-segment clocks. Yes, they were the familiar "click... click..." digits that surely any would-be passenger has watched mesmerized while waiting for that (where IS it?) train to arrive.

In the course of conversation, the question of EPE designing a suitable electronic interface for these digits came up. Would Tech Ed be interested? Certainly, was the author's timely response to a novel design idea. The resulting basic design is capable of driving from one to eight digits, with expansion up to 64 digits possible. They can be controlled via a standard 4 × 4 data entry keypad, or via a PC-compatible computer running under MS-DOS or Win95/98/ME. A PIC16F84 microcontroller is the controlling device between the PC or keypad and the multiplexed digits. The PC software is written in QBasic/QuickBASIC, but can be run as a standalone program without the need for QB to be installed.

These digits are ideal for use in any situation that requires a large electronically controlled display, where the data is to be input intermittently. Applications that come to mind are sporting scoreboards, ticket draw results, display of the outdoor temperature in public arenas - well, you've seen where large digits can be used, think up your own applications!