Talk:Wiegand effect

Wiegand keycards Besides sensors, the Wiegand effect is used for security keycard door locks.[2] The plastic keycard has a series of short lengths of Wiegand wire embedded in it, which encodes the key by the positioning the wires in two rows. Wires that represent zero (0) bits are placed in one row while wires that represent one (1) bits are placed in the other row. The wires are evenly spaced so as to create consistent timing between bits without the need for any clocking. The card is read by pulling it through a slot in a reader device, which has a fixed magnetic field and a sensor coil. As each length of wire passes through the magnetic field, its magnetic state flips which indicates the sense of the data bit. The resulting Wiegand protocol digital code is then sent to a host (system) controller to determine whether to electrically unlock the door. Wiegand cards are more durable (and difficult to counterfeit)1 than barcode or magnetic stripe cards. Since the keycode is permanently set into the card at manufacture by the positions of the wires, Wiegand cards can't be erased by magnetic fields or reprogrammed as magnetic stripe cards can.

1 The relative difficulty in counterfeiting Wiegand cards is due solely to the limited availability of the wire. Really not that difficult as wire can be scavenged from other cards.

Wiegand keycard readers Original version Weigand readers read the data encoded in the swiped card by using a fixed magnet to set the polarity of each wire as it is passed into the reader. A magnet of the opposite polarity positioned near a sensing coil causes the wire polarity to flip generating the characteristic Wiegand pulse in the coil. The generated pulse has sufficient energy to drive the connected data line low without amplification or conditioning. Later version Weigand readers added signal conditioning the could discriminate valid pulses, eliminate oscillation that sometimes occurred in the coil. The pulse width and inter-pulse timing is now controlled to guarantee the parameters to the pulse received at the access control system panel. Wiegand Man (talk) 04:04, 29 September 2011 (UTC)