The Barcode — The Lines on Every Product in Every Store

This patent describes a system for encoding and reading product classification data using printed patterns of lines, dots, or bulls-eye circles that vary in width and spacing. A light source illuminates the printed code; a photoelectric reader detects the varying light reflectance as dark lines absorb light and light spaces reflect it. The resulting electrical signal pattern — a series of wide and narrow pulses — corresponds to digits or letters that identify the product. The patent covers both the printed code itself and the optical scanner that reads it. Woodland and Silver's original concept used concentric circles (a bulls-eye) rather than lines, but the linear barcode proved more practical for manufacturing.

The clever bit

Bernard Silver overheard a Drexel University food chain executive asking a dean to find a system to automatically read product information at checkout. Silver told his graduate school friend Woodland, who became obsessed with the problem. Woodland was sitting on a Miami beach in 1948 when he absentmindedly drew lines in the sand with four fingers — then realized the varying widths of his lines were exactly what he needed. He extended the concept of Morse code (dots and dashes in time) into spatial patterns (wide and narrow lines in space). The patent was filed in 1949 and granted in 1952, but the technology sat dormant for 20 years until lasers and cheap computing made real-time scanning practical.

What it does not cover

• ×The Universal Product Code (UPC) standard — the specific encoding system adopted in 1974 was developed separately by the Uniform Grocery Product Code Council
• ×2D barcodes (QR codes, Data Matrix) — these encode data in two dimensions rather than one and were developed decades later
• ×RFID tags — radio-frequency identification is a different technology that doesn't require line-of-sight optical reading
• ×Laser scanning — the original patent used incandescent light; laser barcode scanners came in the 1970s