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I look for an RFID tag that gives you the option to 'choose the output'. For example, you want to choose an RFID-output from a list of X possible outputs using a multi-directional switch with X directions.

Does something like that exist? What resolutions of X are there available? How small can it be?

If not, how could you go about designing the thing? Just slide the antenna over the desired Chip from a number of X chips and do some debouncing? Or use just one chip but connect one out of its X inputs with a further circuit and a debounce?! (and what type of circuit?)

Furthermore, how does one tackle higher resolutions for X without making it bulky (as there is just not enough room to make it work with debouncing and different chips and the mechanics and all)?

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    \$\begingroup\$ Sounds like you want to build an RFID emulator: a microcontroller that emulates one (or more) "dumb" RFID tags. Example: dimme.net/rfid-tag-emulation-with-an-avr \$\endgroup\$ – 0x6d64 May 5 '15 at 14:11
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    \$\begingroup\$ It's really unclear what you are asking \$\endgroup\$ – Andy aka May 5 '15 at 14:11
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    \$\begingroup\$ Ox6d64 understood op. I also thought the question was clear. \$\endgroup\$ – Passerby May 5 '15 at 14:46
  • \$\begingroup\$ Would it work to simply have several readers next to each other, and you touch the tag on the reader of interest? This could be emulated by some sort of antenna switch, so you only need one reader... \$\endgroup\$ – tomnexus May 5 '15 at 17:34
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    \$\begingroup\$ @tomnexus no readers are immensely expensive and potentially bulky. I probably actually need some form of ox6d64's emulator. I'm curious what ready-made forms exist. \$\endgroup\$ – helperhelper May 6 '15 at 7:52
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RFID tags are simple. A dedicated microprocessor with an eeprom, and a coil. Passive tags derive their power from the RFID field of the reader, and then respond with their eeprom contents, either a serial number or string. Simple. You can make one with any microcontroller if you follow the standard. If you want a tag that can be selective of the string it outputs, then you use standard microcontroller circuits and programming to get that done. The RFID part can be just the microcontroller, a coil (or inductor), and maybe a capacitor.

A DIP switch and a few input pins:

schematic

Pseudo code:

   SetupRFID()
   While(1){
    ReadInputs()
      If Input1 + Input2 + Input3 + Input4 == 4
      then TagOutput == String4
      else if Input1 + Input2 + Input3 + Input4 == 3
      then TagOutput == String3
      else default TagOutput == String0
      delay for 1 second
    }

Aside from the link that @0x6d64 provided (http://dimme.net/rfid-tag-emulation-with-an-avr/), there is also http://scanlime.org/2008/09/using-an-avr-as-an-rfid-tag/ and http://hackaday.com/2011/09/26/barebones-pic-rfid-tag/

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