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32

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 ...


14

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

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 (...


11

Stop doing 'as many turns as I can allocate' and start doing 'the right number of turns'. As the loop gets larger, the self capacitance and the inductance increase quicker than you think, and you don't need as many turns. Start with one or just a few turns of your target size, and see what capacitor is needed to resonate it down to 125 kHz, or see what the ...


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 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 ...


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

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.


9

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 ...


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

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 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

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

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

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 ...


6

The magnetic field from a magnet is static. In order to induce a current and/or voltage you need a changing electro/magnetic field. Typically the field that RFID uses for operation has a frequency of at least 120 kHz but typically 13.56 MHz. That's much faster than you can practically generate by physically moving the RFID card around a magnet. So near a ...


5

If you are looking for a semiconductor fabrication house, this begs the question: Approximately how many million units per year would you be paying for? The IC manufacture business does not generally do one-off designs, nor one-off fabrication runs. There are supposedly "boutique" semiconductor fab houses that do short runs, but if they really exist any ...


5

It's all about power. Passive RFID tags work by transmitting power from the transmitter to the tag (typically three orders of magnitude more than the data signal), and then communicating with the tag at various frequencies (13.56 MHz, 433 MHz, and 900 MHz band being the most common). The transceivers on these chips operate in the hundreds of µW range (...


5

My personal feeling is that direct WiFi is not the best solution given that you need extended battery life and you are only transmitting minor amounts of data. Another aspect is that your system only appears to be transmitter ---> receiver. No bidirectional comms are needed (from what I can tell) and this will push-down the battery usage. Given the range ...


5

Wifi is probably hopeless for this application. You should use a sub-1GHz ISM band radio instead. The Texas CC1101 and Nordic nRF905 are both quite good. The CC1101 has an edge on power consumption I think. Texas also have some newer parts, such as the CC1120, that are on-air compatible but a bit more sensitive. In any case using sub-1GHz bands will give ...


5

Many tags use 125KHz and 13.56MHz. Your likley in these 2 bands. Other UHF and 2.4GHz If your is a passive tag (most low cost tags, designed to work within a few inches, are passive), for sure and definite answer, I have used Radio Frequency spectrum analyzer with tracking signal generator and 1 to 2 inch diameter, self make loop antenna, Scan freq range ...


5

No. RFID is very much a master-slave relationship, in which the master (the RFID reader) supplies both power and timing to the slave (the RFID chip). There's simply no way for two masters or two slaves to communicate directly with each other. For such a short distance, optical communication would make the most sense. IR transceivers are commonly available ...


5

The easiest way would be with the nRF24L01. These modules cost on ebay 1€. with these you can exchange data in higher speed and lower cost. You connect them via SPI, like with the RFID Module. This is one of the most known designs out there. There are also many other designs with a PCB antenna or with an external one. Range with the Black one is about 60 ...


5

By and large, RF (particularly RFID) simply won't work underwater, particularly at the depths associated with crab pots. RF attenuation of seawater is just too great. Note figure 7 of the paper. At 1 MHz, attenuation is ~40dB/m, and pots at 100 meters down simply aren't going to hear a transmitter of any reasonable power, much less retransmit their IDs. ...


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