Hot answers tagged

24

Digikey sources their parts from the manufacturers and adds a retail mark up. The alibaba seller takes remnants from someone's production run (or possibly salvaged parts, or if you're unlucky counterfeit or reject parts) they don't pay full price. Usually it's remnants, someone makes 10000 products and has 500 parts on the last 3500 part roll left over and ...


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 ...


13

First idea: RFID. One tag (very cheap) underneath each piece. Each tag should identify which type of piece it is (out of {6 white}+{6 black}=12 different types). One transceiver circuit and a 1-to-64 multiplexer for the whole board. Also, 64 little antennae, each one underneath each board position. The transceiver operates at a very low RF power (you should ...


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 ...


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

The frequency is low enough for measurements with oscilloscope. Add a small few ohms resistor in series with your antenna. Be sure that the resistor is not a coil. It must be resistive at the operating frequency. Feed with a signal generator a sinewave into the antenna at the right operating frequency. Measure at the same time the voltage and the current ...


9

I would say that they are probably counterfeit,this is a well known problem when buying from china, you cant be sure that they are original unless you are buying from a trusted chinese supplier. Most of the time they work alright if you are not pushing them to the spec limits,here are some links that can help you through this problem of chinese counterfeit ...


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

@DoxyLover and the others are right: the master was pulling up, causing driver contention. My mistakes were: Assuming that configuring the I2C peripheral (alternate function in STM jargon) would automatically set SDA as open drain. In my bit-banging code, configuring the wrong port for open drain (leaving SDA still push-pull and leading me to believe that ...


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

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 ...


7

To open up my answer I will use information from the Android developer page, first sentence from sub heading Tag dispatch system: Android-powered devices are usually looking for NFC tags when the screen is unlocked, unless NFC is disabled in the device's Settings menu. This indicates that the device is using current to power the antenna continuously, ...


6

How about this document about antenna design for the PN512? The rectangular antenna on page 47 looks like it will meet your needs. Texas instruments also makes some fairly decent HF antenna design guides. I've fabricated some of these rectangular antennas for 13.56MHz NFC before (the ones specified by TI), they're fairly simple and work well as can be ...


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/


5

You may consider to do this application with Bluetooth. The market is more the driving factor than the technology. Allow me to explain: BT will be cheaper and easier to implement Wireless is better in this app than the others (sound, light etc. variations) since child movement will not impact wireless' performance, all others are susceptible to motion of ...


5

The answer is yes. The reader (phone) has to scan continuously to see if it is there. Even if this does not happen at the hardware level, it would be possible to continuously "ping" the reader coil via firmware, so again the answer is "yes" - this will continuously drain the battery.


5

Self latching power-up circuit: You seem to be overly concerned with the risks involved with a device holding itself on. This is essentially how just about any device with only push-button normally-off switches works - extremely common and standard. eg any push-on push-off LED torch with a non latching switch, and those with multiple functions with ...


5

Your friend is talking through his hat, they're related but not the same. If you read the wikipedia page about NFC you can read there that: NFC is a set of short-range wireless technologies, typically requiring a separation of 10 cm or less. NFC operates at 13.56 MHz Remember that value of 13.56 MHz Then read the wikipedia page about RFID and scroll ...


4

I've seen many electronic chessboards that have a hole drilled in the center of each of the 64 squares, with a simple photodetector under each hole, which gives only 1 bit -- "nothing here", or "a piece of some kind is covering the detector". This requires (a) some memory and code to remember the old configuration of the board, and to track which piece moved ...


4

How about a plastic plate on each car with large, clearly readable numbers and letters? Say, one on the front, and one on the back. Let's call these 'number plates'. Then have a camera at the entrance of the garage which contains some kind of computer which can read the numbers, and pass them along to another computer for processing. Then you can record ...


4

I'm no expert on 13MHz-carrier data-transmission but i do come from a background of transmitting power magnetically to rotating circuit boards and receiving modulated data back at 80MHz so if I've misunderstood anything please let me know. •Could it be acceptable to put the components (NFC controller, LED > driver) on the same PCB as the NFC antenna? Yes ...


4

Yes, it is quite possible to make passive tags secure, but the tag must have some local processing power, not just a static read-only memory that it reads out. The general algorithm is called "challenge-response". The reader and the tag share some secret piece of data, but this data is never transmitted over the air. Instead, the reader chooses some random ...


4

Adafruit's PN532 board has been meticulously designed in order to get the maximum range out of it: PN532 - Breakout Board. That being said it is possible to increase the range by using a powered(active) tag instead of an unpowered (passive) tag. For your problem it sounds like it needs to remain passive, but so long as you get the antenna to be as close to ...


4

Zero unless the phone is transmitting, which it isn't most of the time. Note that the circuit in the link you posted only works 1. shortly after the phone is turned on, 2. while talking on a call, 3. while sending a text. So for any given 5 second period, your harvester is almost certainly not going to get any energy from the phone at all. Now, when your ...


4

Some people told me I can replace it if the hz was a multiple. The fact it don't work as expect. Is it normal ? Next time, better take a look at the data-sheet. The PN532 wants to see a 27.12MHZ xtal or external clock of the same frequency. You can't just pick a different clock-frequency. You shouldn't have any problem finding the correct xtal online. ...


4

These antennas are from NXP evaluation boards. These metal parts lower the field-strength output because of the induced eddy currents. They also detune the antenna and the matching network quite a bit. Without doubt the antenna would perform better without these metal squares, but NXP put them in to show that their NFC solution will work in a real-world ...


3

NFC/RFID Tags based on operation frequency are divided to many sections. 13.56 MHz and 125 kHz tags are the most popular. It is obvious 125 kHz reader/writer can detect only 125 kHz tags and the same is true about the 13.56 MHz ones. 125 kHz tags usually are memory-less devices with a unique ID and middle distance detection range. These are used in many ...


3

Look for RFID tags, and RFID sensors. This RFID reader from SparkFun has a built-in antenna and a range of 200 mm and works with inexpensive 125 KHz RFID tags. Also, SparkFun has this USB RFID adapter to connect to a reader such as above, and provide USB data read off the tags directly to your computer or other device. If you need to span a large area such ...


3

It's a good idea. In fact I think the first time I heard it was 25 years ago :-) and it probably existed before. Very broadly I can think of two approaches to distance measurement (between two points, so ignoring triangulation). Measuring trip time and deriving distance by knowing the velocity or measuring power drop and deriving distance by knowing the ...


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