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MMA845X simultaneous vibration and motion detection

Question asked by Joe Snyder on Dec 19, 2014
Latest reply on Dec 23, 2014 by Joe Snyder

I am working on a project where the intent is to use an MMA8452 to sense 2 separate conditions.  In short, it's a PCB to be mounted in a cell phone case, and LEDs will go on 1: if the phone vibrates and 2: if you physically pick the phone up.

 

I already have the PCB made and reflowed, and it's sending the interrupt to the micro when you pick it up.  All the hardware works just dandy. 

 

My problem is that I have the threshold set up around 1.3 G's (on all axes) so it doesn't trigger with every little movement of the phone - only when you physically pick it up.  With that threshold, it's not enough to trigger on the vibration of the phone.  .    

 

Does anyone have any advice on how I could interrupt on a tiny movement (like vibration), and a larger threshold movement (like picking it up) at the same time?  It's going to be driven on coin cells, so power consumption is critical - I don't want to be constantly switching back and forth with different settings and checking status every few ms.

 

I know, it's asking for 1 device to do 2 things at once, but thanks in advance for your thoughts.

 

Joe

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