The “Wiegand Interface”
The “Wiegand Interface” has been the most popular technology for connecting card readers to door controllers for years. Though the interface is widely used and somewhat understood by many security system professionals, many of the finer details may be a mystery to some. We will review the history, take a deeper look into the technology, and examine some future card reader trends and alternatives that hopefully will broaden the reader’s knowledge.
History of the Wiegand Interface
Wiegand card readers came about after a scientist named John Wiegand applied a principle called the Barkhausen Jump to discover the “Wiegand Effect”, where specially treated wires produce magnetic fields. These wires, when built into a plastic security card, are spaced apart in a pattern and arranged in two rows corresponding to 0’s and 1’s. They produce a data stream when passed or “swiped” through a slotted card reader containing a magnet.
The data stream is then transmitted over two wires, DATA 0 and DATA 1 (typically green and white) to a door controller that was designed to receive such an output from the reader. Note that only one bit is transmitted at a time, nominally with a pulse width of 100 micro seconds and a pulse interval of 1 msec.
Wiegand cards and readers were manufactured by two companies, primarily Sensor Engineering in the U.S. and on a smaller scale by Doduco in Germany (the cards and readers from the two companies were not cross-compatible). Since the manufacturing of the cards was so specialized, requiring custom machines to pull and twist the wire in a precise manner such that it would gain the properties to produce the Wiegand Effect, cards were virtually impossible to duplicate and hence considered extremely secure, especially when compared against magnetic stripe cards.
Although actual Wiegand swipe cards and readers have disappeared from the access control system landscape, the Wiegand Interface for communicating with an access control panel (controller) survived because virtually every controller made worldwide already supported the interface. Thus, the vast majority of proximity and smart card readers, biometric readers, push button transmitter/receivers, keypads, and other similar devices continue to be designed and built with a Wiegand Output.
The Wiegand Hardware Interface
A reader or device with a Wiegand Output typically has an exit cable or a terminal strip to support the reader functions, typically 5, 6, or 7 conductors or points. The wires or terminal points correspond to the following functions:
Red – Power, typically +5 or +12 VDC
Black – Ground
Green – Data 0
White – Data 1
Brown – LED Control (allows red, green and amber, no “off” state) and sometimes beeper control in the case of 1-line LED control, or Red LED in the case of 2-line control
Orange – Green LED in the case of 2-line LED control
Blue – Beeper Control, in the case of 2-line LED control
With 1-line LED control where a 5 conductor cable is typically used, and the LED control line (brown wire) is held high by the controller, the LED is red. When pulled low it turns green. When toggled at a specified rate it appears amber. The beeper control may be tied to the LED control; when pulled low for a green, it also activates the beeper to indicate the door is unlocked.
With 2-line LED control, the red and green each have their own control wire or terminal, and either is pulled low to display the appropriate color. When both lines are low, the LED is amber. When both are high, the LED is not illuminated (off); a state not provided with 1-line control. Also with 2-line control, the beeper has its own control line, allowing it to be activated independently of the LED state. Customers will choose 1-line vs 2-line control based on what their manufacturer’s controller supports – not all support the superior 2-line control.
The Wiegand Software Interface
Originally, most Wiegand swipe cards contained 26 Wiegand wires corresponding to 26 bits of data. The bits were broken up into Facility Code (FC) and ID Number fields, with Bit 1 and Bit 26 being reserved to calculate parity for error checking. Two 26 bit formats existed, 8/16 (8 bit FC, 16 bit ID) and 12/12. 8/16 allows for 256 unique facility codes (0-255) and 65,536 unique IDs (0-65,535) within each facility code, while 12/12 allows for 4096 of each (8/16 eventually became the predominant format). Access control system manufacturers designed their software to be able to support 26 bit Wiegand format, which is still widely used today. An 8/16 “format sheet” as used to describe the data used by the manufacturers would look contain something like the following information:
A problem arose however because 24 data bits doesn’t really allow for enough unique numbers to ensure non-duplication of cards. Initially, Sensor Engineering would provide 26 bit cards by spreading different facility codes in each geographic area to minimize the chance of duplicate cards ending up near each other and causing a potential security problem. Soon however Sensor, in conjunction with OEM access system manufacturers, developed custom card format with larger bit counts to allow for greater number ranges, OEM control of the programming sequences as well as acceptance by the controller and their software, and minimal to zero chance of card duplication. Custom Wiegand formats usually ranged from 32 to 37 bits, but with advancements in proximity and smart card technology, bit counts can now go much higher.
The Good and the Bad of the Wiegand Interface
The Wiegand Interface is a widely used term that is understood by some and thrown about liberally by many, and by some who don’t really understand its ins and out, and its pros and cons. The good news is that the Wiegand Interface is something that virtually all manufacturers of access control systems support. For instance, with Keri’s Doors.NET software, customers can either choose an existing format from the Credential Types library or create their own data format to match that of the card and then save it to the library. There are a plethora of reader manufacturers of all types whose products’ data output is via a Wiegand interface, giving customers a wide range of choice of solutions that best meet their needs.
The bad news is that it is easily misused by customers who don’t manage their card sequences properly. Cards are often duplicated (especially 26 bit) posing a security risk, and customers sometimes misorder cards and/or choose a format that doesn’t really suit their needs. As stated earlier, 26 bit Wiegand format still constitutes a large share of the market and is used on many “high end” projects, yet it should only be used in the lowest security applications.
The Wiegand Interface allows for only one way communication, that from the reader to the controller. There is no back and forth communication to provide the system operator with otherwise critical information about the reader, or to update the reader’s firmware. Additionally, cable distance between reader and controller is limited to 300’ (90m) with standard #24 AWG wire (0.6mm) reader cable and 500’ (150m) with the more expensive #18 AWG wire (1.2mm) wire.
Alternatives to the Wiegand Interface
Readers that allow for two-way communication such as those that communicate via RS-485 provide a number of advantages. Keri’s NXT Series Readers are one alternative, and a soon-to-be-growing trend toward OSDP (Open Supervised Device Protocol), another RS-485 interface technology.
- Readers can report their status to indicate if they have a problem, as opposed to a Wiegand-type reader, where one doesn’t know about a problem until someone tries to access the door and reports that the reader isn’t working
- Readers can report their firmware revision and receive a new revision via download when necessary
- RS-485 based readers allow for much longer cable runs, up to 1000’ (300m) or more, and require only a 4 conductor cable
- Keri’s NXT cards are never duplicated, so security is high
The Wiegand Interface is here to stay, at least for the foreseeable future. Customers should be armed with the best information they can about it, as well as its alternatives.
Dennis Geiszler is a 30+ year veteran of the access control industry, serving in various sales and marketing executive positions for both Indala Corporation and Keri Systems.