Magnetic keys for coffee machines

[Rostfrei]

pcf7931as

I really don't know if this part of the forum is the right place for the question, but I don't know where else to fit it.
Does anybody know how this magnetic keys (I think so as there are no metal connections on it) work?

**broken link removed**

This keys are used in our office for the big coffee machine. When I insert it to the machine I can fill it up with money and the machine writes the value on the key. Every time get for cup of coffee the value decreases according to the price.

Anybody knows the theory behind this keys? How they work?

Regards,
Rostfrei

 

[TekUT]

magnetic coffee key

Usually there is a wireless link trough one oscillator into the coffee machine and one antenna on the key side (this system is also know as transponder) the coffee machine generate a high-freq signal that is linked to the key, this signal is used to supply the key and also modulated in order to transfer information from the coffee machine to the key and back from the key to the main coffe machine. To store credit usually is used a simple EEPROM.

Bye
Powermos

 

[FvM]

nxp pcf7931as

A common RFID standard, e. g. 125 kHz may be used for the system.

 

[RF-OM]

philips pcf7931as

It is probably not RFID but rather NFC device. NFC is stands for Near Field Communications. It already widely used for security devices e.g. access card. Soon such devices will be integrated into cell phones and then phone became your ID and credit card and much more. Plastic credit card will be obsolete soon. The idea is to use inductive coupling between transmitting and receiving parts for communications and to provide some electrical power for card or key.

 

[FvM]

coffe machine nfc

Usually NFC would be regarded as RFID technique.

For small tags and proximity access, low frequency techniques may be better suited to my opinion, but 13.56MHz proximity standards (ISO14443/Mifare/NFC) could be used as well.

 

[RF-OM]

coffee key rfid

Yes, these two technologies are close but there are differences too. NFC used for very small distance and usually do not require separation of signals as for RFID systems in warehouse. Couple of years ago I work a little bit for NFC project and nobody called it RFID, I believe it is separate technology.

 

[FvM]

machine magnet key

NFC specification is describing different operation modes, single passive device detection is one of them. An anticollision protocol as found with any other RFID technique is included in the specification as well and there are many references to targets and similar. So it's not far-fetched to my opinion to regard it as RFID technlogy.

The other point is, that single chip memory tags (that have to be supplemented by an "antenna" coil only) are available for all common RFID standards from various manufacturers(I'm not sure regarding NFC). So it's obvious to design a product as the said "magnetic key" around an existing RFID tag chip.

 

[Rostfrei]

rfid coffee key

I opened the yellow key you can see on the photo and found out that there is a Philips chip marked PCF7931AS in there. I couldn't find the data sheet for it, but I found some links about what it is

**broken link removed**
https://www.bicotech.com/?page=prod_tu&lg=en

I also found some memory organization document which I appended here. Does anybody have datasheet for this chip?

Regards,
Rostfrei

 

[Rostfrei]

chip card for coffee machine

I also found this link

https://www.nxp.com/#/pip/pip=[pfp=53457]|pp=[t=pfp,i=53457]

 

[Rostfrei]

www.bicotech.com

Immobilization page from NXP

https://www.nxp.com/#/aip/aip=[aip=149]|pp=[t=aip,i=149]