Telepen

Telepen is a name of a Barcode symbology designed in 1972 in the UK to express all 128 ASCII characters without using shift characters for code switching, unlike Code 128 does, while only using two different widths for bars and spaces. Unlike most linear barcodes that specify the encodings for each representable character, Telepen only defines 4 basic bar-space modules:

• narrow bar-narrow space for bit 1
• wide bar-narrow space for bit sequence 00
• wide bar-wide space for bit sequence 010
• narrow bar-wide space for bit sequence 01 or 10 (the meaning alternates, so 01110 is encoded as 01 1 10 where the first and the third module is the same).

The scheme allows to encode all even parity bytes, and can even be used for a continuous bitstream.