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Thread: Connect to sensor on rotaing wheel

  1. #1

    Default Connect to sensor on rotaing wheel

    Hi, i am doing a project in which i have to place an accelerometer sensor on a rotating disc or wheel.
    The problem is, it is difficult to connect the +ve,-ve and data pins while the disc is rotating.

    Please tell me how this can be done.

    The only idea i have till now is use rings and contacts for each and every input output, is there any better way to do it?

    Thank you.

  2. #2
    Administrator T-1000 vikas's Avatar
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    Use slip rings , its the simplest and cheapest way

    http://www.homebuiltrovs.com/slipringreel.html

    3 line slip rings for power and single tx serial line

    Possibility -
    Maybe use inductive coupling for power and then rf ic to transmit data
    Vikas Patial

  3. #3
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    Slips fail very often, especially in small dimensions and if hand made. Put a huge cap in between the power lines. Also, Hope your accel do not have a digital interface. You will get junk if you use slips. Use very low power and at least rated voltage.

    Apart from the slip, i would recommend a tiny rechargeable battery, accel and a small RF module to be bundled as a package and kept at the wheel. This is reliable. Use SMDs if possible. We had made a similar module with a PIC 12F, MMA1260 and the cc2500 along with a small 3.6V nicad, but for a different application. The total size came close to 20mmx14mmx20mm. The size can be further reduced if a smaller battery or a smaller accel (say- LQFP - but i have no idea how to solder them at a hobbyist place) was used. MMA1260 was a bit bulky. Also choose your 'g' rating wisely. That matters a lot, in fact.

    The operating voltage of MMA1260 was 4.5-5.5 V as per datasheet, but it did work at 3.6V, giving proportional acceleration values. Our application did not require a precision reading. If yours need one, do operate at rated voltage.
    .... I didnt do it ! ....

  4. #4

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    Hi Vikas,

    Inductive coupling sounds like a great idea. I haven't worked on this before.
    Doesn't the inductive coupling cause interference in the radio channel and other circuits placed on the wheel?

    Thank you.

    PS: Change of plan, for now i am placing a servo motor to test how it is going to work, instead of the accelerometer. So three wires to the wheel
    1) 5v power supply
    2) Ground
    3) PWM signal

  5. #5

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    for slip rings try using a 3.5 mm audio jack? Its can work well for intermitent use

  6. #6
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    Just cant understand how a servo can replace an accel in any kind of testing.

    And yes.. with servos, I will never recommend slip if the servo will be taking at least 1Kgcm torque.
    .... I didnt do it ! ....

  7. #7
    Senior Member Cyborg
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    Quote Originally Posted by asimov_18 View Post
    for slip rings try using a 3.5 mm audio jack? Its can work well for intermitent use
    You make my day, maybe this will solve long pending designs. Not sure this has already been use somewhere, atleast not to me. Just has to work on friction part and structure stablitiy.
    Nikhil Chandra | Bangalore

    Imagination is more important than knowledge.

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