freefall detection using MMA7455L accelerometer

Pyro Project Ideas/Requests
raj0757
Newbie Pyro
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Joined: Fri Dec 02, 2011 12:16 am

freefall detection using MMA7455L accelerometer

Postby raj0757 » Fri Dec 02, 2011 12:26 am

MCU used : pic18f4520
Accelerometer : mma7455l ( digital output, 3 axis, spi interface)
Simple program when detect freefall turn led on

Many thanks in advance, hope In this world of genius , someone can help me in initial stage of my work.

ThePyroElectro
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Re: freefall detection using MMA7455L accelerometer

Postby ThePyroElectro » Sat Dec 03, 2011 12:16 am

Hi,

I like this project idea. What is your definition of free fall in terms of time and acceleration?

I know some laptops have similar detection equipment for turning off hard-drives when +/- 1g is detected.

To me, free-fall for any commercial device would be when acceleration > 0.6 G or acceleration > -0.6 G consistently over a period of 0.1 miliseconds

Does that sound like a good basis for determining free fall for a project?

raj0757
Newbie Pyro
Posts: 3
Joined: Fri Dec 02, 2011 12:16 am

Re: freefall detection using MMA7455L accelerometer

Postby raj0757 » Sat Dec 03, 2011 3:13 am

Hi
Thanks for your reply,
Can you send me any sample project with code and schematic
I want this accelerometer to interface with pic18f4520. Initially If I am able to turn LED on when freefall occur, its enough for me.

Setting for Freefall Detection
LDPL bit in Control Register 2 (Address: $19) should be “1” for freefall detection. When the output values of all enabled axes
are below the threshold limit value, logic high level is output to INT1 or INT2 pin and indicates the event was detected.
– If LDPL = 1 and all three axes are enabled for detection
– When the condition below was detected, Logic high level output to INT1 or INT2
– “XOUT ≤Threshold" and “YOUT ≤Threshold" and ”ZOUT≤Threshold"
– Threshold limit value is common for all three axes. Positive/negative and absolute value option is available.
– INT1/INT2 pin assignment for level detection is controlled by Control Register 1 (Address: $18). Detection status is also
able to be monitored by Detection source Register (Address: $0A). Once the event was detected, INT pin or register bit
will not be cleared until clear bit in Interrupt Latch Reset Register (Address: $17) is set.
For a more detailed description of the Threshold Detect please refer to application note AN3571, “Threshold and Pulse Detect
Using the MMA745xL”.

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I find many useful examples from your website. You are doing great work.


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