rfid activation

Discussion in 'The Projects Forum' started by rfhelp, Mar 23, 2009.

  1. rfhelp

    Thread Starter Active Member

    Mar 23, 2009
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    Hello,

    My project is to use a push button send power to an rfid module (12vdc out) The rfid is a passive 2" prox unit so I need to be able to remove the fob while maintaining a 12vdc output. In a perfect world the rfid unit could power down after it has tripped the relay but not the end of the world if it has to stay powered up.
    When the push button switch is pressed again turning the power off and resetting the system. The system cannot be activated again until the rfid fob is recognized.

    I have the rfid module wired up right now with an automotive relay but it shuts down when the fob is out of prox. There must be a way to use the rfid as the switch instead of the power source?? He says hopefully....

    I have been told by a couple electronics guys locally it can't be done. Are they right?
     
  2. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
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    Do you have the datasheet for the RFID Reader, and the schematic of the circuit you have so far?

    One way would be using Logic ICs, diodes, transistors, or relays (last choice) to make an "AND" gate for the On Switch, so the on would only work if RFID and switch were engaged. The Off wouldn't need the RFID, but you might want a timeout on "off" so the machine isn't left running with somebody else's credentials.
     
  3. rfhelp

    Thread Starter Active Member

    Mar 23, 2009
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    no I don't have the data sheet
     
  4. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
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    Do you have a schematic or wiring diagram of how it is currently hooked up so that it works only when the RFID is present?
     
  5. rfhelp

    Thread Starter Active Member

    Mar 23, 2009
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    sorry for the double posting,

    Here is my crude rendition of what I have
    [​IMG]
     
  6. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
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    Does the RFID reader give a 12V output, or are you using a transistor to drive the relay?

    The way I am reading it, the input from the switch is only switched to the relay if the RFID "fob" is present, or is the entire RFID Reader disabled when the switch isn't turned on?

    You want to have it latch on when the RFID "fob" is present, but allow it to be turned off without the RFID "fob" present?

    Is the switch a momentary pushbutton, or single pole dual throw lever type?
     
  7. rfhelp

    Thread Starter Active Member

    Mar 23, 2009
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    Yes, rfid is 12vdc out
    switch powers the rfid module but no power to relay until fob is present
    need the relay to stay active when fob is not present until power it cut (then reset) without switch on no pwr at all to rfid.
    switch is either or ( I am using a three contact rocker right now and am ashamed to say I don't know if it is spdt or dpst or what. It has three terminals and is a two position on/off latching rocker)
     
  8. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
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    Is there a reason the RFID reader needs to be powered down when the machine isn't running?

    The solution is an SR Latch. With the Set driven by RFID + Switch AND gate - What you already have set up with the switch powering the RFID reader. The Reset would be the other pole of a SPDT switch, not connected through the RFID reader. The output of the SR Latch would then drive the relay.
     
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