reading bar codes

reading bar codes elektor may 1981 — 5-43 One bar per bit; eight bits per byte; sixteen bytes per printed line and 64 lines per Kbyte ... that"s more than eight thousand bars spread across several pages, which will all have to be trans- lated into logic ones and zeros without errors. The light pen Since black bars reflect less light than white spaces, it would seem a simple matter to read them by scanning the pattern with a photo transistor. A Ik Simple computer programs are already being printed in bar code form for calculators. Naturally there must be a reliable means of reading them at high speed. This requires two essential items: a good quality light pen and an intelligent measuring system. accuracy of about 0.1 mm! Not so easy to construct after all ... Never mind, there are various suitable types available ready-made on the market. Hewlett- Packard have manufactured the HEDS-1 000 light sensor shown in figure 1. The light source consists of a small LED and the sensor itse...