1. iknaite

    Thread Starter New Member

    May 23, 2012
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    I m using ADXL362 accelarometer as a motion sensor with microcontroller.
    how to use accelerometer as a motion switch to give power to the microcontroller when motion is detected. Otherwise, no power is given to the microcontroller.
     
  2. ErnieM

    AAC Fanatic!

    Apr 24, 2011
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    If the micro is given no power then what other component will read the ADXL362 digital output and then control the power?
     
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  3. spinnaker

    AAC Fanatic!

    Oct 29, 2009
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    AND how is an accelerometer supposed to generate power when it is a sensor that actually consumes power itself?


    Sounds to me like the OP did not think this project through.
     
    Last edited: Jan 13, 2013
  4. MrChips

    Moderator

    Oct 2, 2009
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    Sounds like an over unity or perpetual motion project to me...

    ... unless there is an outside chance that the OP means to switch ON the power to the microcontroller.
     
  5. THE_RB

    AAC Fanatic!

    Feb 11, 2008
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    It's not an unreasonable request. From memory, some of the new accelerometer chips are designed for micro power standby mode, and have a special output pin that is activated when movement is detected.

    Normally that would be used to shake the uC out of sleep mode, so it wakes up and then gets new data from the accelerometer. It may be possible to have that same signal actually power up the uC with a FET etc, but I doubt it would save that much power as many of the new micros have nA sleep modes anyway.
     
  6. ErnieM

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    Apr 24, 2011
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    Ah ha, and this device does have a Wake-up mode where it partially runs using a low current, and when shaken awake (literally) will change the state of an interrupt pin.

    That interrupt pin could control the power to the rest of the circuit. I've done this using a low dropout regulator (LDO) as many have an enable pin: if you can match the interrupt pin level to an enable (enables I've seen typically work when they go high) then this could work together nice.

    Depending on the micro controller it may be capable of doing a wake on pin change, but that leaves the power to other components an open question.
     
  7. ErnieM

    AAC Fanatic!

    Apr 24, 2011
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    I saw your other thread was closed... to make that interrupt pin work you need to understand the data sheet for your device to see those settings.

    There will also be some other circuitry involved as you also want some other signal (PIC pin?) to enable power so you can control it going on and off. There's also a "chicken and the egg" problem here: how does this thing turn on the very first time? Without *any* power applied I would expect the accelerometer forget it's state information so an alternate way to turn it on when power is first applied is needed.

    A button would work but is very very crude. A discrete flip flop could work: power applied sets or resets that, which enables power, allows the state info to be programmed, and then can power down things leaving the accelerometer control.
     
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