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31

Because RFID doesn't work based on wave propagation. It's thus not actually a radio system (despite working at "RF"=Radio Frequency). Think of an RFID tag more as the secondary side of an air-core transformer, where information is transmitted by the tag changing the amount of power it draws from the primary side of the transformer, or by charging a energy ...


23

NFC is a type of RFID. Not all RFID devices use NFC. NFC is a bundle of specific technologies and protocols used to communicate with storage devices (often credit cards or passive identifier tags). The NFC specifications cover everything from the radio frequency used (13.56 MHz) and the types of modulation used, to the communications protocol used to read ...


19

They don't. They store a number which is internally represented as binary and transmitted as binary. There is no hexadecimal here. Humans have a hard time grasping numbers with large number of digits. We therefore often represent large binary numbers in hexadecimal when intended for human understanding. We have gone so far as to make the tools we ...


16

They punch holes in RFID cards all the time. Using a hand or desk hole punch. The smarter companies order them with the holes pre punched. A hand hole punch is fine if you are no where near the coil or IC, otherwise you risk breaking the coil. You may also risk opening the inner layers of the rfid card to the elements if you open it in the wrong place. The ...


13

Passive tags are powered from a antenna in the environment. The tag then puts a varying load on the RF field, which the transmitter detects. This varying load is a digital bit stream with the tag's ID, checksum, and sometimes additional information. This system inherently works at close distances. To get enough power to a tag for it to run 5 meters away ...


12

Glass is chosen because of it's chemical composition. Certain glass formulations are very close to the composition of bone, making it very biocompatable, and the composition can be tweaked for various behaviour (mostly regarding the way nearby tissue reacts). Furthermore, you are far, far overestimating the issue of the capsule breaking. Any trauma ...


11

This idea might be patented, so it might not be suitable for a commercial project, but you can actually measure the position and orientation of one electronic device relative to another, with reasonable accuracy, using magnetic fields. This is how Polhemus and Ascension trackers work. They are used in VR motion tracking, and in surgery for tracking the ...


11

A simple radar should give you some idea. If it's inside a small enough cage, possibly a near-field effect-on-a-tuned-circuit type of system would work, instead of needing a pulse-type radar. This may not be a perfect indicator - it could be hard to tell the difference between being in the midst of a number of conductive planes, and being inside a complete ...


11

You're confusing radio communications through the air with coupled inductors. To communicate through the air using a 125 kHz carrier you would need an antenna of around 1/4 lambda so about 600 meter long in order to transmit that 125 kHz effectively. Obviously RFID does not work this way. RFID uses coupled inductors which means there are two coils (...


10

This stripe is a patch antenna, which is nothing else than a wire, printed on a PCB or similar, that radiates like an antenna. The unconnected strip on the right is likely a reflector element, which doesn't receive any current from a direct connection but is electrically coupled with the rest of the patch to improve the radiation properties or the input ...


10

Almost certainly a typo. Note that the s key is right next to the d. But it may also refer to the new "Radio Frequency ISentification" technology, of course :-). edit after your question update The abstract talks about "intelligent guide to help blind people to solve puzzles". It's easily imaginable that RFID could be used to identify the puzzle pieces.


10

Technically it stores a 96 bit binary number, and hex happens to be the most convenient way to express that number to humans. Digital systems see everything in ones and zeros. If the number was in decimal it would have to be represented as binary in the hardware anyway. e: If you're asking why it's 24-digits, I assume it was chosen because that will allow ...


10

The left hand side of the board in the 2nd to last picture contains two PIFAs (Planar inverted F antenna). Looks like one is 2.4 GHz and one is 5 GHz. It appears that the ZBS242 chip is a Samsung SOC with a built in IEEE 802.15.4 ZigBee radio. I can't find much information about it, and the pages I have found are in Korean. Figures. http://eplus.co....


10

An antenna converts a low impedance transmission line (from the chip or also via a coax or stripline) to a high impedance at the end of the antenna. The high impedance is to suit the impedance of free space (377 or 120\$\pi\$ ohms). An antenna does this gently and in doing so creates a standing wave along its length in order to allow the current to gently ...


9

The short answer is "no". The NFC ring will not contain the application-specific cryptographic keys required by Oyster. NFC "rings", like other NFC-capable contactless payment tokens, contain a tamper-resistant microprocessor with cryptographic acceleration and a small amount of secure memory storage. These chips and associated induction antenna coil are ...


9

Simply put, the antenna does not radiate - it operates more as a coupled inductor. The coupling drops with \$r^3\$ rather than \$r^2\$ (if I remember right). You have calculated the wavelength, so you can see how small the antenna is as a fraction of the wavelength. With larger antennas, maybe a few meters, and higher transmit powers, its possible to get ...


8

I will add to Clabacchio's "maybes". As he says, the stripe at right is probably a resonant element of some sort that couples to the main loop and modifies its properties in a way that they hope will be advantageous. The loop in the bottom left corner (shown below) will be a coupling loop that provides transformer action between the main loop and the load. ...


8

I found a nice answer to my question here: http://www.secureidnews.com/news-item/is-the-debate-still-relevant-an-in-depth-look-at-iso-14443-and-its-competing-interface-types/ Short summary of the article: The first interface was type A, supported by Mikron and their Mifare technology, later bought by Philips (NXP). Some limitations quickly occurred: the ...


8

This is a surface-mount RF module, so you need to make a PCB to solder it on, unless you do some freestyle wire soldering. You also need an antenna, a GPS module, a microcontroller, voltage regulator and battery. For the device to run from a reasonable battery for a month, will take a strategy on when to power on the RF module and the GPS, and even to take ...


7

I think the radio part is the least of your problems. To my best knowledge most car openers use a cryoptographic system called "rolling keys", which means that recording what the keyfob sent and replaying it won't work. Microchip has extensive libraries to go with thier chips intende for this purpose, but you need to sign a non-disclosure to get it. Here is ...


7

You cannot read a passive 125 KHz Tag with a NFC reader, because as you have already guessed, they operate on different frequencies. There are passive RFID cards operating on 13.56 MHz, however, and these will read just fine on a NFC-enabled phone.


7

I can only relate my experiences: - If you want to detect a normally-not-powered passive type tag at extreme distances you have to power to that tag from a significantly bigger magnetic field. Making your magnetic field stronger is the only way I can know (and can recommend). Making your tag more efficient in recovering a fraction of this power is also part ...


7

In summary, When using a NFC standard loop coil antenna, sized about 4x4 cm, the theoretical maximum working distance is 20 cm. In practice, the range for reliable communication is much smaller, usually about 5 cm (4 times smaller). How could you improve the range without tweaking the power level and sensitivity of the NFC devices (master/transponder and ...


6

Scrabble Flash, or Boggle Flash, as it's called here, uses infra-red to communicate between tiles. I took mine apart and took some photos: http://www.flickr.com/photos/54388270@N04/sets/72157625390551633/


6

VOLTAGES USED IN THIS CONCEPT ARE LETHAL. ZAPPERS CAN KILL THE EXPERIMENTER. EVEN A SMALL CAMERA FLASH CAN KILL AND ADDING LARGER CAPACITORS AND/OR HIGHER VOLTAGES CAN KILL YOU EVEN MORE! (Being dead once is more than enough) It's doubtful whether this query well matched to the aims of this forum. The schema shown shows the general principle but ...


6

You are using a sledgehammer to swat a fly. Bike frames have serial numbers already, usually underneath the main crank. When you first get your bike, record the serial number. If you can provide that to the police, they can easily check it and verify it's your bike. Even better, when you buy the bike, make sure the serial number is written on the receipt,...


6

Generally RFID operates on near-field interactions. This is language that make something simple sound much fancier then it is. When you are in the near field of an antenna any coupling is due to capacitive and inductive coupling. Most antennas for such a system are actually just large loops of wire and the tag often has a similar construction. The ...


6

I'd use a colpitts oscillator. In fact i've just been designing one at 250MHz. Here's the general design: - The diagram shows a 50MHz oscillator but if you use a high-speed transistor that has an Ft of 5GHz or above you'll get decent results at 500MHz. If you want it to work at 3V3 make R3 = 2k2 and R1 = 1k. I'm trying to remember the transistor I used - it ...


6

It's not that the plane will block transmission in one direction, but that it will absorb much of the power you put into the antenna, and also greatly change the antenna characteristics. The plane is in the near field, which means the antenna can "see" it. It will cause the electrical properties of the antenna to be quite different than when there is no ...


6

Yes, it can be done with a rack of discrete transistors, resistors, capacitors, and other components. After all, that's what's in the chips you don't want to use. While it can be done, it would be very tedious, expensive, difficult to get running, and large. Even if the reason is to avoid learning about chips and microcontrollers, this still doesn't make ...


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