Advice needed for micro IMU to Bluetooth transmission project

Discussion in 'The Projects Forum' started by David Brooker, Mar 11, 2015.

  1. David Brooker

    Thread Starter New Member

    Mar 10, 2015
    3
    0
    Hi all

    I am currently working on a project for an electrical device but my knowledge of circuitry is very limited. I have done some research online and I think I’m on the right lines but would really appreciate some guidance if at all possible please.

    The complete unit needs to be as small as possible. So far I am unsure exactly what I need and how small the components can be, how much power they would require and how much it would then weigh, so I guess any advice to answer these questions would be great.

    Initially I believe I need an IMU that can measure very small movement up to around an inch. The movement would include pitch, roll & yaw. I then need to instantaneously transmit the data via Bluetooth. As far as I can work out I would need a Microprocessor but I may be wrong.

    I am also thinking that the unit would need to have something included that would activate the device or at least the Bluetooth transmission. I was either thinking a hall effect sensor or perhaps activation via a very sensitive pressure switch.

    I've been looking at the Sparkfun 6 degrees of freedom but this seems too big. Also the Arduino Pro Mini, Sparkfun BLU Mate 2 and the Sparkfun US1881 Hall Effect Sensor. Like I mentioned, I'm not sure exactly what components I need and it all needs to be really small. Basically, I'm a bit stuck.

    Any advice would be really appreciated. Thanks in advance.

    David
     
  2. sirch2

    Well-Known Member

    Jan 21, 2013
    1,008
    351
    If you could make your own circuit board then it could be made pretty small (couple of inches?) but if you are plugging together a set of prebuilt modules then it is going to be bigger.

    Why do you need to "activate" the device, why not just leave it running? How frequently do you need updates over bluetooth? A microcontroller can switch on and off the bluetooth if battery life is a concern.

    These IMU's are tiny but would still need a MCU and bluetooth chip. One final question why bluetooth and are you aware of it's range limitations?
     
  3. David Brooker

    Thread Starter New Member

    Mar 10, 2015
    3
    0
    Thanks for the reply Sirch.

    The device will need to trace small movements and send it to an app. The way it is transmitted is not relevant but the range required would only need to be a couple of meters. I would need to have a switch of some kind as it needs to be triggered / activated at a particular time and in short bursts rather than sending irrelevant data. For example, a pen that transmits a letter written upon contact with the paper or writing surface, perhaps with a magnet or pressure switch? A bit like a smart pen but for singular letters or very small words.

    I need to squeeze all that into something about 15mm x 3".

    Cheers
     
  4. sirch2

    Well-Known Member

    Jan 21, 2013
    1,008
    351
    Most modern microcontrollers have inbuilt timers so could trigger transmission at time intervals or it could trigger on a particular IMU change, but if you want a Hall sensor then they are not large so that is the least of your worries.

    The SENtral module I linked to is 22mm by about 10mm and an MCU and a bluetooth chip would fit in the remaining 53mm but how are you powering it? The biggest single thing by far will be the battery, how high can it be?

    As I said, if you make your own board (or get one made, possibly multilayer) it can be pretty small but I would suggest getting it working from modules or on bread board and then miniaturizing it.
     
  5. Reloadron

    Active Member

    Jan 15, 2015
    967
    234
    Keeping this in mind:
    For a sensor you may want to consider a 3 Axis Accelerometer along the lines of those in the link. As to a micro-controller there are plenty to choose from but the Arduino Family are easy to work with and have off the shelf add on modules including Bluetooth Modules for Arduino. So you start with a sensor that will meet your needs, maybe in the 3 axis types linked to, select a micro-controller, and finally a means to connect like Bluetooth.

    I suggest this approach and using modules only because unless you have worked with and done soldering of tiny discreet components modules make things easier. The discreet component approach is a good way to go if you are comfortable with it and is less costly.

    Ron
     
  6. David Brooker

    Thread Starter New Member

    Mar 10, 2015
    3
    0
    Thanks for the advice guys. Seems the PNI sensors will do the job.
     
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