MMA8451 Accelerometer algorithm for accident detection

[pawan kumar]

Greetings,

I have interfaced MMA8451 I2C based accelerometer with microcontroller. I can continuously receive some X,Y,Z values and display them in the hyperterminal. In my project, I have to detect an

accident and raise an interrupt to the controller using this chip. Any ideas would be a great help to me.

Thanks in advance,

Pawan

 

[klystron]

What is your definition or specification for an accident?

 

[pawan kumar]

Hi klystron,

I want the mechanism through which the airbag of a car gets activated. In this event, I mean that severe an accident.

Pawan

 

[klystron]

Specify the acceleration ( negative) level, direction, the jerk, the required reaction time to deploy the bag and how will you filter false sources like somebody bumping the console, closing the bonnet ... Specifications are measurable. Without detail specifications you do not understand the problem and your solution will most likely fail

 

[pawan kumar]

Hi klystron,

My complete project is integrating LPC2148 with GSM and GPS module to track the location and send a msg in case the user needs to track the vehicle. It also reports in case there has been an accident.I purchased an accelerometer to serve this purpose. I have just a week left for the final submission. In case I did not do anything with the accelerometer, I plan to use a switch interrupt. In short, I demonstrate it with a toy car. So, pls suggest me a solution which rises an interrupt when the car hits the wall.

Thanks,

Pawan

 

[klystron]

The research of crash acceleration specifications should have been research at the start of your project. That is the main purpose of the project. Take a look at www.accidentreconstruction.com/newsletter/jan08/velocity_pulse.pdf

 

[pawan kumar]

Thanks klystron,

I could observe from the article that when an accident occurs, there is a sudden change in g from 0-.1g to upto 15g within a short interval of .02s . I need to program the accelerometer such that it alerts the interrupt whenever a threshold is reached.

Pawan

 

[DatsAbk]

Hi Pawan,I've decided to use the same accelerometer for tilt sensing application.Could you please post the schematic of the connection in the following thread or mail them at abk.edu@gmail.com....my mail id.

I am confused about connection of mma8451qt vddio pin with my 5V controller.Since it runs on 5V and its logic output levels are 5V,could you help me out with this?

- - - Updated - - -

Hi Pawan,I've decided to use the same accelerometer for tilt sensing application.Could you please post the schematic of the connection in the following thread or mail them at abk.edu@gmail.com....my mail id.

I am confused about connection of mma8451qt vddio pin with my 5V controller.Since it runs on 5V and its logic output levels are 5V,could you help me out with this?

 

[pawan kumar]

Hi DatsAbk ,

You can neglect the VDDIO pin. I had used only the VDD(pin-14) , Gnd(pin 12,10 ), SDA(pin 6),SCL(pin4) [both pulled up to 3.3v] ,SA0(pin 7) and INT1(pin11) for the interface. I had purchased the IC with an in built voltage regulator and pins expanded from nex robotics ( **broken link removed** )
Hope this helps.

Pawan

 

[DatsAbk]

Thanks bro....Will need help ahead in case the same doesn't work.

Could you Private message me ur mail address

 

[pawan kumar]

All the best and yeah.. I ll PM you.

 

[Twisted_transistor]

Hey Pawan.. at d moment I'm tryin to interface my MEMS MMA8451 with LPC2148.. I just want it to detect a demo accident and indicated by turnin an led ON.. But I've never worked with I2C before so could u pls help me by mailin me d code for the above task? My review is on d 24th..

Thanks in advance

 

[Jigar 4 Electronics]

@ pawan kumar, Well according to me you do not need to have 3 axis accelerometer for this project.
Just use a single axis (less sensitive accelerometer will also suit to your project, in short sensitivity should not be an issue)
then put the accelerometer perpendicular to the earth.
set the threshold value for a noticeable jerk.
and do the program for it.

but as you've buy the 3 axis accelerometer then you can take a benefit of all of 3 axis.
set their threshold in a best possible way according to the orientation of placement.

- - - Updated - - -

@twisted transistor,
check the link, https://www.nex-robotics.com/produc...tal-accelerometer-with-voltage-regulator.html
scroll down & you will find the tutorial of it with LPC2148

 

[pawan kumar]

@twisted transistor,

as Jigar 4 Electronics says, I followed the same code samples from nex robotics.

I configured all three axes to a small threshold level . It raises an interrupt when the threshold exceeds.

You may download the full source code of my project HERE

Regards,

Pawan

 

[Twisted_transistor]

ok.. Thanks alot.. both of u.. Pawan & Jigar
But pawan ur code is soo big.. Is it possible for u to only send me d portion reqd only for d mems? like without d gsm portion n all.. I would like it to be a single prog.. I know its asking too much.. can u help me?

 

[Twisted_transistor]

Hi Pawan, in your code i.e. "i2c.c", there are a lot of registers used like I2C0CONSET, I2C0CONCLR, etc. I have been checkin online for the description of these registers but could not find it anywhere. Could u pls tell me wer I can find the configuration of these registers?

Thanks in advance

 

[Jigar 4 Electronics]

@pawan kumar, Which frequency have you used ? 100kHz or 2.25MHz ?? I am using the same sensor from nex... I am not able to have proper reading.
the same code is working perfectly with my other sensor which is also uses I2C intefacing.
I am using ARM Cortex - M4F based LM4F120H5QR controller.

when I've scan the I2C bus it gives the acknowledgement at every addresses!!! I mean starting from 0x00 to 0x7E ...
I think the sensor has damaged.

Can you please share your experience?

 

[pawan kumar]

@Jigar 4 Electronics :

I had used the standard clock rate (100Khz). You say that the same code works for another sensor. Is it the same component? also, try interfacing the (damaged) sensor with another mcu too. That would eliminate your variable of doubt on damage in sensor.

Regards,

Pawan

 

[Jigar 4 Electronics]

Thanks for your response Pawan,

Can you tell me about pull up resistor value?
Have you used the breakout board as it is or have you changed the value of pull up resistor?