How to disable/enable RFID passive card using logic level?

RFID switch off

Hi

Could anybody give an idea about how to disable/enable simple RFID passive card using logic level . Used RFID card is passive card with antenna tuned to 13 MHz and parallel connected to 2 wire rfid chip .

The task is to permanently disable RFID card when it is needed , so , if reader will try to access passive RFID card, it wont be possible .

I have some proposals , but do not know whether they will work properly or not :
- Use analog low resistance switches and put at the place where antenna connected to RFID chip (or n and p channel mosfets ). Switch power have to be more or adjusted if rfid antennas output voltage will go higher than current power .
- relay is not suitable due to low power requirements
- Fuse - not known whether control's low power supply - 2-3 V 10 ma will capabale to burn fuse .

Customer does not want to order new custom rfid chip with control pin and prefers to use existing available one .

Any other ideas ??

Re: RFID switch off

Where do you want to do this "disable"? in reader or tag?

RFID switch off

Disabling is going to be done in tag . It sounds stupid ,
but Customer want to have security device integrated with RFID card and when burglar alarm wil be detected
the RFID card must be passivated . As far as there is
only 2 pins on chip in parrallel to tuned LC I can only cut induction to prevent card from making response TX
to reader .

Re: RFID switch off

I can not understand the situation but am very interesting.
If you want permanently disbling tags, why not throw them away?
If you want disbale the tags at some condition, why not disable the reader? and afterwords enable it. It is always easy to disable the reader from a alarmimg signal or in reverse. A passive card need a interrogate signal and the power from the reader to wake up it.

Re: RFID switch off

Reader send code to tag. Tag decode it. If code is correct tag respond. If not it is silent.

Re: RFID switch off

For passive tag, there is no special code from reader to tag. Only a signal at tuned frequncy to "power" the tag and "powered" tag send the ID to the air.

Re: RFID switch off

HeiFelix said:

I can not understand the situation but am very interesting.
If you want permanently disbling tags, why not throw them away?
If you want disbale the tags at some condition, why not disable the reader? and afterwords enable it. It is always easy to disable the reader from a alarmimg signal or in reverse. A passive card need a interrogate signal and the power from the reader to wake up it.

Click to expand...

The tag is attached to mcu controlled device with alarm sensor . It is battery powered and very small size . There is alarm sensor on device . If it triggers
then RFID must be made nonfucntional - so if reader will attempt to read and write into card it will not be possible . There are differents ways to make the card nonfunctional :
- Burn tag's chip
- electrically controlled cut of tag's antenna via analog switch or fuse burn
- Some other ways - that is what i am asking for .

It was tested that if antenna will be cut the rfid becomes nonfunctional.

The idea is not to giver immediate alarm , because device can be in unattended places , but when device attached to something will pass checkpoint , the reader will attempt to read the card there and if it will not be readable - alarm will be generated .

let say you put device and lock to the baggage . To be able to open baggage device must be mechanically unlocked because its contruction is done in a way that locks baggage key . When unlocking is done the mcu will detect it and switch the RFID off (disable and make nonfunctional ) .

This solution is proposed to use for moveable object supervision , to detect whether there was access to these objects or not .

Re: RFID switch off

Hi:
Now, I understand you application and it is quite interesting.

I think the tag was made by another company and the mcu controlled device was made by you.
You may have two ways to do "disabling"
1. touchless solution. You can made another resonate circuit(a saw resonator cicuit) to send "noise" at the tuned frequncy of tag when you need to disable it. The reader will not able to find the head of the tag's message and ignore it as a noise.
2. Tag chip solution. Add a relay or analog ciucuit to cut the antenna require more space on tag. But, there are maybe some other pins which could be used by you to disable it. For example, you can give Vdd and Vss signal( from you MCU)on MCRF355(just an example) to guide the tag into progamming mode, then no message will be sent unless you cut your signal.

Am i right?
HeiFelix

RFID switch off

The problem is that tag must be disabled permanently even if battery will be fully discharged.
So it is not possible to transfer permanent noise on
Rx freq .

Proposed tag's chip has only 2 pins directly connected to antenna .
Relay is not possible to use because of low power requirements .

Re: RFID switch off

If a tag can send data passively, the noise can also be produced passively.
Use a passive RFID chip which works at the same frequncy as the tag. when it is woke up by a reader, it send the pulse periodic to cover the delay(anti-collition) and TX time of the tag. The periodic pulse can be pre-programmed, I am not quite sure if it can works for such a long time to cover that time.
For some passive chips, you also can controlled the "noise producer" by two pins from MCU to enable/disable it in a very low power consumption.

RFID switch off

The switch off can easely be realized with connecting the high speed diod rectifier bridge to transponder coil and putting bjt transistor in rectifier output . When transistor opened voltage on coil will not be above Vopen + 2*Vd of diodes ~ 1.3 V - that should not be enough to run transponder chip . While transistor is closed its Cce capasitor will be charged and no voltage and coil resonance freq will be influenced and n additional requirements on bjt frequency chars.

The one question is unclear - what is the min voltage on coil to run transponder chip ?

Any opinions ?