Electronics notes/RFID and NFC notes

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It's intended to get an intuitive overview for hobbyist needs. It may get you started, but to be able to do anything remotely clever, follow a proper course or read a good book.

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And some more applied stuff:

IO: Input and output pins · wired local IO · wired local-ish IO · · · · Shorter-range wireless (IR, ISM RF) · RFID and NFC · bluetooth · 802.15 (including zigbee) · 802.11 (WiFi) · cell phone

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Audio notes: See avnotes

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Less sorted: device voltage and impedance, audio and otherwise · electricity and humans · power supply considerations · Common terms, useful basics, soldering · PLL · pulse modulation · signal reflection · resource metering · SDR · Project boxes · Unsorted stuff

See also Category:Electronics.

RFID, NFC, contactless smart cards

This article/section is a stub — probably a pile of half-sorted notes, is not well-checked so may have incorrect bits. (Feel free to ignore, fix, or tell me)

RFID (Radio-frequency identification) refers to a radio-frequency communication.

It often refers to a few specific designs, most of which are small and fairly easily hidden, particularly in/on/as small surfaces, relatively hidden devices.

On power

There are:

  • passive tags
which use an external source of power - often the communication itself (the reason for the large coiled antennae?)
can be very small and thin, and therefore almost invisibly embedded in many things.
common, because you don't need to care about power at all
  • active tags
battery-powered (...so limited lifespan and more expensive)
can signal autonomously
can be used over considerably larger distances
can often communicate faster
  • battery assisted passive (BAP)
active tags that take negligible power from their batteries until triggered by communication
cannot signal autonomously

Frequency use

This article/section is a stub — probably a pile of half-sorted notes, is not well-checked so may have incorrect bits. (Feel free to ignore, fix, or tell me)

Sorted approximately by common use:

  • Low-frequency - 120-150kHz range
for many countries often specifically ~125 or ~134.2 kHz
these are more or less interchangeable
You can fairly easily get readers (and writers) for this.

  • High-frequency - 13.56 MHz (worldwide ISM(verify))
Used in access badges, bank cards, library cards, loyalty cards, etc.
Example: Mifare (which is sometimes known for )

  • Ultra-high
    • 433MHz
    • 868MHz (EU unlicensed) and ~915MHz (US unlicensed) (think ISM)

  • Microwave
2.4Hz and 5GHz - expensive tags

In term of 'what's in your wallet', it's probably mostly ~125 / ~134 kHz, and 13.56 MHz (verify)

Security criticism

RFID/NFC blocking wallet

Notes on cards and protocols

This article/section is a stub — probably a pile of half-sorted notes, is not well-checked so may have incorrect bits. (Feel free to ignore, fix, or tell me)

Proximity card

Early proxcards hold about as little as a magnetic stripe card.

Originally and mainly passive cards (typically at 125kHz, and correlated with ISO 7810 ID-1 sized cards), powered by the reader so must be held close.

Active proxcards have a battery (lifetime generally on the order of a few years), and may be contacted at 2 meters or so, and a few more, useful for things like automated toll collection, gate opening, and such.





NFC (Near Field Communication) can be thought of as an extesnsion.

It refers to things conforming to to ISO 14443 (proximity, ~10cm max range) or ISO 15693 (vicinity), and RFID usually refers to quite varied systems mostly described by the older ISO 18000.

In practice, the fact that RFID and NFC are used somewhat fuzzily means that people often use

RFID to mean older simpler identitying (and often 125kHz) implementations,
and NFC to mean mean newer, fancier, communicating (and often 13.56MHz) implementations.

The best way to be sure is to figure out the specific tech being used.


Contactless smart card

This article/section is a stub — probably a pile of half-sorted notes, is not well-checked so may have incorrect bits. (Feel free to ignore, fix, or tell me)

Seems to refer to cards with

a read-only CSN/UID
a read-write IC
some basic security
usually in a ISO 7810 sized card (but also in keyfobs, etc.)

...which makes them a little more complex than classic proxcards.

Typically at 13.56 MHz ('RFID HF')

Protocols vary, but MiFare is one of the largest.


ISO 14443 - proximity cards at 13.56MHz
Type A and Type B, same protocol but varying modulation, coding, init
ISO 15693 - vicinity cards (~1meter) at 13.56MHz
ISO 18000 - varied systems at different frequencies
below 135kHz
at 13.56MHz
at 2.45GHz
within 860MHz .. 960MHz
at 433MHz


Biometric passports


Contactless payment

The acronym originally stood for its creators, "Europay, Mastercard, and Visa" https://en.wikipedia.org/wiki/EMV



NFC tags







EU identity cards


See also