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Magnetic Induction — Parallax Forums

Magnetic Induction

HumanoidoHumanoido Posts: 5,770
edited 2010-03-12 05:57 in Propeller 1
The plan is to set up a couple prop chips to serially communicate
using a simple magnetic induction circuit.

Can anyone recommend a design to accomplish this?

humanoido

Comments

  • LeonLeon Posts: 7,620
    edited 2010-03-11 11:30
    en.wikipedia.org/wiki/Near_Field_Communication

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    Leon Heller
    Amateur radio callsign: G1HSM
  • HumanoidoHumanoido Posts: 5,770
    edited 2010-03-11 13:16
    Leon: I'm looking for the low frequency inductor version that has greater range to 1.5 meters.
    The site does not show any circuits. The small range described is established with wired
    air cores. I think we need longer range with magnetic core wiring.

    humanoido
  • kwinnkwinn Posts: 8,697
    edited 2010-03-11 13:41
    @humanido, I may be wrong but isn't the purpose of the core to concentrate the magnetic field inside the core. Perhaps it might work if you use a reasonably long ferrite rod to wind your inductor on, but most of the other core shapes are designed to confine the field.

    You might start here: http://en.wikipedia.org/wiki/Very_low_frequency
  • localrogerlocalroger Posts: 3,452
    edited 2010-03-11 13:44
    humanoido, how big can the comm coils be? Induction falls off by an inverse-cube instead of inverse-square law so it's really a very short range phenomenon.

    You could really use any scheme for low-frequency radio, just using the final tuning coils as antennas instead of a wire. Make both ends tuned circuits at the same frequency, excite one at the right frequency with the prop when you want to send a 1, and rectify what the other receives. You will still probably need amplification to detect what you receive.
  • LeonLeon Posts: 7,620
    edited 2010-03-11 15:17
    You'd be much better off using ordinary 2.4 GHz wireless chips, like the Nordic nRF24L01+. They are used in wireless mice and keyboards, and are very cheap.

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    Leon Heller
    Amateur radio callsign: G1HSM
  • PhilldapillPhilldapill Posts: 1,283
    edited 2010-03-11 19:39
    The nordic chips seem like they might be what you're looking for, humanoido. I haven't gotten around to using it, but I've been wanting to for a good bit of time now. Leon, don't you have some Propeller or PIC code for it?
  • LeonLeon Posts: 7,620
    edited 2010-03-11 19:47
    I've got some PIC18 C18 test code:

    www.leonheller.com/MiRF%20V2/

    It's a rewrite (with improvements) of the code on the SparkFun site. Interfacing their modules to Propellers should be quite easy, I've provided a schematic for the PIC18F45K20. I don't think I've actually tried that board, earlier boards using the PIC18F4520 work OK. I only get a range of a couple of metres indoors, with the old MiRF V2. SFE messed up the PCB and put a ground pad underneath the ceramic antenna. They fixed the problem on the current modules.

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    Leon Heller
    Amateur radio callsign: G1HSM

    Post Edited (Leon) : 3/11/2010 7:59:38 PM GMT
  • HumanoidoHumanoido Posts: 5,770
    edited 2010-03-12 03:11
    Thanks for the information - every comment is very helpful and I appreciate the input.
    Core-less inductors will work if the range is not too little or too great.
    Ideal range is about the size of a small children's swimming pool, or 1.5 meters is minimum.

    Sparkfun has a transceiver.
    www.sparkfun.com/commerce/product_info.php?products_id=691
    but the price is $20. That's still more than a Parallax IR emitter receiver pair.
    (I'm comparing the inductor communications with infrared.)
    It doesn't seem like much cost for one unit but eventually multiple props will multiply
    this and it will be too expensive.

    I looked for the price of the single chip. There are many news announcements and
    references to "low cost" but I never found the actual cost of the chip.
    www.nordicsemi.com/index.cfm?obj=product&act=display&pro=101

    The first idea was to use a common small inductor with a supporting resistor
    /capacitor with the driver (modulator and serial data stream) in prop software. The receiver
    would be a small antenna. That's because the design must be very simple, draw ultra low
    power, and be very small in physical size (no larger than a prop chip).

    Do you think either inductive or 2.4Ghz transceivers can beat out infrared in cost,
    power consumed, size, and simplicity?

    humanoido
  • LeonLeon Posts: 7,620
    edited 2010-03-12 03:38
    That's the wrong part. This is the correct page:

    www.nordicsemi.com/index.cfm?obj=product&act=display&pro=94

    I'll ask my distributor for current pricing. I bought some but it was a long time ago.

    TI/Chipcon makes a similar chip, but it's much harder to use.

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    Leon Heller
    Amateur radio callsign: G1HSM

    Post Edited (Leon) : 3/12/2010 3:53:43 AM GMT
  • HumanoidoHumanoido Posts: 5,770
    edited 2010-03-12 04:29
    Leon: Thanks, that link led to a page with a data sheet download
    which provides a sample circuit. It requires some supporting components
    including a 16Mhz crystal, decoupling capacitors, bias resistors, and several
    nH inductors with 50 ohm single ended output (for RF) and no obvious info
    about how to use it for transmit or receive, frequency, modulation, etc.

    humanoido
  • LeonLeon Posts: 7,620
    edited 2010-03-12 05:57
    It's all in the data sheet. For instance, page 8 tells you that it uses 2.4 GHz and GFSK modulation. It's controlled via SPI.

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    Leon Heller
    Amateur radio callsign: G1HSM

    Post Edited (Leon) : 3/12/2010 6:05:51 AM GMT
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