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Wiegand-For Dummies

deer in the headlights

Recently, our CEO, David Carta, called me into his office and asked me, “Mark, what is Wiegand?” He was instructing a new Telaeris employee about XPressFreedom, our Wiegand to Ethernet converter which we use to enable mobile access control with existing system. He thought that I, as our sales lead, should be able to give an appropriate explanation. Like a deer in the headlights I froze, knowing that I did not have a solid, technically sound answer. Feeling the gaze of our newest employee upon me, I threw a panicked cookie-cutter answer against the wall, hoping that it would be satisfactory. It wasn’t and I knew it. Worse, I knew Dave knew it. Fortunately, he didn’t lambaste me in front of our new co-worker, but as I left the room, my tail was hanging between my legs.

Later that day, Dave called me into his office to address the encounter from earlier in the day. Part of Telaeris’ culture is to deliver the very best support and knowledge to our clients, in our efforts to be the worldwide leader in mobile access control solutions. As our primary salesperson, he wanted to be sure that I could provide top notch technical knowledge, in order for me to provide the very best service possible to our customers. Dave’s instruction to me came in the form of a challenge, “Mark, I want you to write our next blog article about Wiegand.”

digging_deeper
Dig deeper to get to what’s important

Simple enough right? With Google and the entirety of the World Wide Web at my fingertips, I did some light research and quickly threw together a rough draft and presented it to Dave. “Mark, this isn’t technically accurate. Go back and dig deeper.” I buckled down and continued to research the history of Wiegand and how it works. I discovered that while the technology started with magnetized wires, today Wiegand refers to an entire interface upon which the access control industry is based. Even more, I learned that I wasn’t alone in my confusion. Many others shared my question, “What is Wiegand?”

John R. Wiegand moved from Germany to the United States in the 1930’s, in order to study piano and choral conducting at New York’s world famous Julliard School of Music. He later became an engineer, but  it was his perfect pitch that allowed him to hear changes that occurred as his wires were magnetized that led to his discovery of the Wiegand Effect in the early 1970’s.

Wiegand wire, patented by Wiegand in 1974, is composed of a magnetic iron-alloy that is designed to form a hard outer casing around a softer inner core. When passed through a magnetized field, the outer shell magnetizes quickly until it reaches full capacity. Once this occurs, the inner core begins to magnetize, and then surprisingly, the core and shell switch polarity. This creates a significant voltage pulse until the wire reaches full magnetization, then it reverts back to its original polarity. These voltage changes are easily detectable.

John Wiegand at his lab bench
John Wiegand at his lab bench

In the late 1970’s, Wiegand and his business partner, Milton Velinsky, developed a card using Wiegand wires for access control purposes. They positioned two separate rows of wires in the card, which when passed over a magnetic field, created varying voltage outputs which are treated as a signal. The Wiegand interface is for readers that could detect these cards output data over two signal lines called D0 (Data Zero) and D1 (Data One). This sequence of 1’s and 0’s mapped to a binary number. Wiegand’s card was seen as an improvement over existing mag-stripe cards which could be re-written easily. Not only could Wiegand cards not be re-written, they were difficult to manufacture, which meant they were difficult to counterfeit.

Card with Embedded Wiegand Wires
Access Card with Embedded Wiegand Wires, the upper row is D0 and lower row D1

This D1/DO interface along with Clock/Data (used for mag-stripe) have persisted since the 1970s as the de-facto interfaces for access control card readers. When most people today talk about a Wiegand card, they are not thinking about a card with wires. Most often they are talking about an RFID enabled card (i.e. Prox, Mifare, iClass, etc.) that outputs card data using Wiegand’s D0/D1 interface.

A Wiegand format is simply a defined series of binary data transmitted over the two output wires. The industry standard for the first decade was a 26-bit format, using 8 bits for the facility code, 16 bits for the user ID. Today, there are many different and custom formats, with the largest being a 200 bit PIV standard used by the US government. The figure below illustrates the use of 26-bit Wiegand.

wiegand26
Standard 26-Bit Wiegand Format

While the Wiegand card is still in production, in the modern access control industry this technology has been largely replaced by newer, cheaper and more secure forms of access cards (i.e. Mifare, iClass, Proximity). The Wiegand interface, however, remains the standard convention for the transmission of data for any device (card, biometric, or PIN reader) to an access control panel.

In conclusion, what began as a simple challenge to learn more about Wiegand, quickly became a fascinating learning experience about the roots of the access control industry. Utilized across a broad scope of access control manufacturers, the Wiegand interface is still the beast of the industry, and it refuses to die off. The use of the Wiegand interface technology isn’t going anywhere in the near future, as the depth of its use far exceeds any up and coming technologies. Nearly fifty years ago, John R Wiegand discovered a cool way to manipulate the magnetic polarity of his custom wires; little did he realize that it would redefine an entire industry.

Two great sources of information, both written by Michael Davis on Wiegand are below:

  1. DefCon 17 Presentation
  2. Machine Design Article

Comments

  1. mike says:

    This is awesome post ……

  2. Good article on the history of Wiegand. I appreciate you taking the time to share.

  3. Giorgio says:

    Good article and explanation couldn’t be clearer.
    I Googled a lot but no explanation is clear as yours.
    I really appreciate.
    Many thanks.
    Giorgio.

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