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I2C query

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  1. Jun 28, 2017 #1
    Hi,

    I have an internet of things project and I am wondering how you would cheaply go about connecting a sensor to an RFD chip? I am a mechanical engineer by training so this is a bit of a learning curve, apologies if it is a really basic and obvious question. I have found this chip:

    http://uk.farnell.com/nxp/sl3s4011f...2?MER=bn_level5_5NP_EngagementRecSingleItem_3

    It makes reference to something called I2C. A quick googling give me the gist that it is for I/O.

    Basically what I am trying to achieve is this:

    1. The reader transmits a signal
    2. The RFID chip receives this signal to provide power (this project requires a passive tag)
    3. The sensor value at that point in time (which will actually just be the voltage value of a variable resistor) is logged
    4. The ID of the RFID chip and data value that was just saved is sent back to the reader

    Have I understood correctly that this I2C pin will allow me to do this? From what I read in the technical documentation I think so. If so would I have to build extra circuitry or could I connect it straight up? I want to use power that is transmitted from the reader. If I am totally wrong would you be able to point me in the right direction. Much appreciated for your help :)
     
  2. jcsd
  3. Jun 28, 2017 #2

    berkeman

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    Staff: Mentor

    Can you Upload a schematic of your uC I2C connections, and a drawing of the overall system please? It's not clear if the I2C connection is in your head-end Master system device, or you slave passive RFID device to the sensor. At least it's not clear to me yet.
     
  4. Jun 30, 2017 #3

    jim hardy

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    2016 Award

    No takers yet ?

    I wouldn't have believed it before looking at that datasheet , but it looks to me like you're right - it just might work....

    To read the value of that resistor will require an analog interface to digitize it.
    and i dont know how you'll power that. If i read right you might get a few microamps from the VDD pin but i'm at a loss what they mean by "I2C on VDD pin". Seems unnatural to use same pin for power and communication.
    Here's a snip from the datasheet http://www.farnell.com/datasheets/1996754.pdf section 13

    upload_2017-6-30_21-8-6.png



    Must be somebody here more current than i am on these things.
    I've only used I2C once twenty years ago with a traditionally powered 5 volt microprocessor. Used a Maxim DAC to produce analog voltage from a digital value i handed it via I2C from my microprocessor.
    You need to go the other way, digitize with an ADC then hand the value to RFID processor via I2C.

    I never tinkered with RFID so can't help, sadly - looks like fun..
    maybe this will prime the pump, though.


    Request a sample and try it out ?

    old jim

    LATE EDIT i'm out of my depth here
    but food for thought....
    micropower ADC
    http://www.ti.com/lit/ds/symlink/ads7924.pdf
    upload_2017-6-30_21-56-30.png
     
    Last edited: Jun 30, 2017
  5. Jul 2, 2017 #4
    Thanks very much for your reply. I decided to go down the route of using an ATtiny10. From what I have read if you connect it up to an inductor you can mimic an RFID tag. I will be experimenting to see if I could also connect up the sensor.
     
  6. Jul 2, 2017 #5

    jim hardy

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    I'm continually amazed at what powerful devices you young folks have available, and how quickly you become adept at using them.


    old jim.
     
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