science

Wiegand interface

Wiegand interface is a science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Wiegand interface rather than just read about it. In short: The Wiegand interface is a de facto wiring standard which arose from the popularity of Wiegand effect card readers in the 1980s. It is commonly used to connect a card swipe mechanism to the rest of an access control system.

Key takeaways

Wiegand interface belongs to science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Wiegand interface to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Wiegand interface from memory before moving on to harder problems.

Reference excerpt

The Wiegand interface is a de facto wiring standard which arose from the popularity of Wiegand effect card readers in the 1980s. It is commonly used to connect a card swipe mechanism to the rest of an access control system. The sensor in such a system is often a "Wiegand wire", based on the Wiegand effect, discovered by John R. Wiegand. A Wiegand-compatible reader is normally connected to a Wiegand-compatible security panel.

Physical layer The Wiegand interface uses three wires, one of which is a common ground and two of which are data transmission wires usually called DATA0 and DATA1, alternatively labeled "D0" and "D1" or "Data Low" and "Data High". When no data is being sent, both DATA0 and DATA1 are pulled up to the "high" voltage level — usually +5 VDC. When a 0 is sent the DATA0 wire is pulled to a low voltage while the DATA1 wire stays at a high voltage. When a 1 is sent the DATA1 wire is pulled to a low voltage while DATA0 stays at a high voltage. The high signaling level of 5 VDC is used to accommodate long cable runs from card readers to the associated access control panel, typically located in a secure closet. Most card reader manufacturers publish a maximum cable run of 500 feet (150 m). An advantage of the Wiegand signalling format is that it allows very long cable runs, far longer than other interface standards of its day allowed.

Protocol The communications protocol used on a Wiegand interface is known as the Wiegand protocol. The original Wiegand format had one parity bit, 8 bits of facility code, 16 bits of ID code, and a trailing parity bit for a total of 26 bits. The first parity bit is calculated from the first 12 bits of the code and the trailing parity bit from the last 12 bits. However, many inconsistent implementations and extensions to the basic format exist. Many access control system manufacturers adopted Wiegand technology, but were unhappy with the limitations of only 8 bits for site codes (0-255) and 16 bits for card numbers (0-65535), so they designed their own formats with varying complexity of field numbers and lengths and parity checking. The physical size limitations of the card dictated that a maximum of 37 Wiegand wire filaments could be placed in a standard credit card, as dictated by CR80 or ISO/IEC 7810 standards, before misreads would affect reliability. Therefore, most Wiegand formats used in physical access control are less than 37 bits in length.

See also Wiegand keycards (Wiegand effect) Access badge Access control Keycard lock Common Access Card Credential Identity document Magnetic stripe card Photo identification Security (physical, engineering) Proximity card Security Smart card

References

External links Open Security Research - Hacking the Wiegand Serial Protocol SIA Standard, AC-01-1996.10 - Access Control - Wiegand Archived 2011-10-08 at the Wayback Machine LayerOne 2007 - Zac Franken - Wiegand Hacked (Video on Youtube) US Patent, System and Method of Extending Communications With the Wiegand Protocol US Patent, Device Authentication Using a Unidirectional Protocol US Patent, Secure Wiegand Communications

Worked examples

Example 1 — a first encounter with Wiegand interface

Start with the simplest possible case. Write down what Wiegand interface claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Wiegand interface before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Wiegand interface ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Wiegand interface

In research: Wiegand interface appears in science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Wiegand interface in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Wiegand interface is common in secondary-school and first-year university syllabi. It links to neighbouring topics Contactless smart cards, Data transmission, so understanding it makes those chapters shorter.
In everyday life: Look for Wiegand interface outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Wiegand interface in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Wiegand interface means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Wiegand interface out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Wiegand interface in simple terms?

Why does Wiegand interface matter?

Because it connects several science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Wiegand interface?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Wiegand interface.