Which Wireless to Use? RF or BT?

Discussion in 'General Electronics Chat' started by pro86, Aug 6, 2014.

  1. pro86

    Thread Starter New Member

    Aug 6, 2014
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    Howdy from Down Under!

    Trying to design some components and require some help regarding wireless options.

    I'm dealing with a complex physical piece of custom made machinery(not made by me). I have a rotating part with +5V and GND available on it and require a very small circuit(less than 25x25mm) connected to a momentary push button switch on this part - to send a signal wirelessly about 3-5m non line-of-sight, with very low latency. Looking for the receiver to be able to trigger an output within less than approx. 5ms.

    Reason I need wireless is the rotating part has a rotary connection supplying power and ground to other components but no more data/signal pins are available to run back through the rotary/wire device.

    Reason for low latency is once trigger signal is high I have to activate some other components with very specific timings.

    The simpler the better.

    The circuit controlling these timing after the event has been designed, a bunch of 556 timers etc, just the wireless hoop I need to jump through now.

    Your suggestions welcome.

    Thank-you & regards,

    Paul.
     
  2. MrChips

    Moderator

    Oct 2, 2009
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    The 5ms latency is the real challenge.

    Here are two possible solutions that comes to mind:

    1) Find a position (e.g. along the rotational axis) to mount an IR LED.

    2) Use a continuously transmitting RF oscillator and modulate the RF output.
     
  3. djsfantasi

    AAC Fanatic!

    Apr 11, 2010
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  4. alfacliff

    Well-Known Member

    Dec 13, 2013
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    sounds like what renashaw uses for its rf touch probes. used for coordinate measureing systems, it spins the instrument to turn on the on timer, then the switch on the probe turns on when the probe touches a part, allowing the machine to measure the parts.
     
  5. THE_RB

    AAC Fanatic!

    Feb 11, 2008
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    I would be trying to modulate the power through the 2 sliprings, and detect that.

    That could be very fast, and much more reliable than a spinning RF transmitter solution.
     
  6. pro86

    Thread Starter New Member

    Aug 6, 2014
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    Thanks for your feedback fellas!

    My responses as follows:

    Mr Chips:
    The arm for which I need this sensor/circuit attached to is not fixed to one rotational axis, therefore mounting an IR LED etc is not feasible.

    djfantasi:
    The arm I need to attach to is hollow at approx. 40mmDIA x 30 deep.
    Thanks for the link to roman black, it was a very interesting read and these are the initial setups we are looking at implementing.

    alfacliff:
    Thanks for your reply regarding Renishaw products, this looks specifically well suited to our application and upon further investigation looking at one of their units RMP60 they can achieve 10ms responses over a hopping 2.4GHz signal which would probably work with our application.


    Other feedback and inputs welcome.
    Thank-you
     
  7. pro86

    Thread Starter New Member

    Aug 6, 2014
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    Thanks THE_RB! We will look into that.

    Any one have any thoughts on using Bluetooth? Struggling to find any latency related info...
     
  8. MrChips

    Moderator

    Oct 2, 2009
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    I still like the idea of IR transmitters if you are concerned with latency.

    Can you mount four IR emitters? IR detectors have very wide viewing angles. They can even detect reflections off walls.
     
  9. pro86

    Thread Starter New Member

    Aug 6, 2014
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    Appreciate your input MrChips. However I'm not convinced this will be an effective solution for our application as we have many other mechanisms moving around the space so LOS and unwanted IR reflections will become an issue. Thanks for your creative input though!
     
  10. THE_RB

    AAC Fanatic!

    Feb 11, 2008
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    Bluetooth transmitters are larger physiaclly, and need to handle bidirectional protocols etc so are likely to be slower.

    You could try the simple OOK (on-off keyed) RF transmitter like the one in that link, and modulate at a few kHz. Then the receiver only needs maybe 10 good received pulses to trigger, total latency a few mS.

    If you say more about what the thing does we can help better. One of the best ways to beat latency is to transmit before you need it. So transmit earlier during the movement.
     
  11. pro86

    Thread Starter New Member

    Aug 6, 2014
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    So I had a thought today as I pulled my laptop out and decided to use my separate wireless mouse.

    I went and grabbed my old Microsoft wireless mouse & use receiver, ripped the cover off & its a 27MHz version.

    Could the mouse inputs and receiver output(USB) be modified for a simple on-off/hi-lo output???

    Any one have any ideas on how to do this because these devices are generally very low latency?

    Cheers.
     
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