What is Wiegand Communication?

Wiegand refers to the technology used in card readers and sensors. Wiegand technology is a wired communication interface that operates between a reader and a controller. Typically, Wiegand technology is found in cards, fingerprint readers, or any other data-capturing devices. 

The Wiegand Interface has been the most popular technology for connecting card readers to door controllers for years. Although actual Wiegand swipe cards and readers have disappeared from the access control system landscape, the Wiegand Interface for communicating with access control panels (controllers) 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.

A reader or device with a Wiegand output typically has an exit cable or a terminal strip to support the reader functions, usually 5, 6, or 7 wire conductors or terminal points that 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)

1-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 green, it also activates the beeper to indicate the door is unlocked. 

2-Line LED Control

With 2-line LED control, the red and green each have their own control wire, 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.  In addition, with 2-line control, the beeper has its own control line, allowing it to be activated independently of the LED state. 

The Good and Bad of the Wiegand Interface

The Wiegand Interface is a widely used term that is understood by some and thrown about liberally by many.  The good news is that the Wiegand Interface is something that all manufacturers of access control systems support.  There are many reader manufacturers whose products’ data output is via a Wiegand interface, giving customers a wide range 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) which poses a security risk, and customers sometimes misorder cards and/or choose a format that doesn’t really suit their needs. The 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 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, the cable distance between the reader and controller is limited to 300’ with standard #24 AWG wire and 500’ with the more expensive #18 AWG wire.