Processes and devices for reading magnetic access control cards

Registers – Coded record sensors – Readout control

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235474, G06K 700

Patent

active

046788972

ABSTRACT:
For reading a coded sequence of magnetic signals recorded on a card, which sequence is formed of bits of identical duration the reading of which results, for the 0s, in a single change of level of an electric voltage, and for the 1s, in two such changes evenly spaced apart in time, the real duration of each bit read is measured, and the time of identification of each bit is adjusted depending on the real duration t.sub.0 of the preceding bit and on the nature of this preceding bit by giving to the time interval T which separates the end of reading of this preceding bit and the time of identifying the following bit, if the preceding bit is a 1, a value T.sub.1 equal to 5/8 of t.sub.0 or to 11/16 of t.sub.0 and if the preceding bit is a 0, a value t.sub.0 equal to 7/8 of t.sub.0, or else equal to 13/16 of t.sub.0 if the bit preceding the above 0 was again a 0 and to 15/16 of t.sub.0 in the opposite case.

REFERENCES:
patent: 3752963 (1973-08-01), Herrin
patent: 3882301 (1975-05-01), Nassimbene
patent: 3887793 (1975-06-01), Goodfinger et al.
patent: 3959626 (1976-05-01), Vinal
patent: 4096378 (1978-06-01), Vinal
patent: 4158436 (1979-06-01), Vanderheyden
Improved Reader for Magnetically Encoded ID cards; Tech Briefs; Computer Design, Jan. 1981, vol. 20, No. 1, pp. 148, 149.

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