Impact direction detection outside a car

[Gronjus]

Hello,

At first, english is not my mother tongue so forgive me if I make mistakes. For my thesis, I have a project to do. One part of this project is to detect a small hit/shock outside the car. I need to get the direction of the shock to make my camera getting to the position where the shock happened. I have been investigating in the MPU6050 ( Tri Axis Accelerometer and tri axis gyroscope) but I got a lot of noisy results and the data is just unusable to get something correct.

I have been investigating too in vibrations sensor but I need to get 4 for the detection. As I want to make the system the smallest possible, I wanted to use an accelerometer.

At this point , I need some tips. What is more suitable for my appliance ?

Thanks in advance,

Gronjus

[Gavinmc42]

Piezo shock sensors can be small
https://www.murata.com/en-us/products/sensor/shock

By using two Peizo elements at 90 degrees and 4 bipolar transistors you can get 8 directions.
The trick it to detect the first shock and ignore the aftershocks, maybe a latching circuit or GPIO interrupt.
Other types are a gold plated tiny ball bearing and metal contacts.

You can also get shock silicon accelerometer sensor types, basically accelerometers with comparators.
http://www.analog.com/en/products/senso ... rpose.html
This one has peak hold
http://www.analog.com/en/products/mems/ ... t-overview
They are getting smarter too, this one does FFT's in sensor.
http://www.analog.com/en/products/mems/ ... t-overview

Sensors for harddisk drives can detect falling and can park the head before hitting the ground.
Even the accelerometers in smart phones are getting more complex, and can now detect shock, gestures etc.

[Gronjus]

Hi,

I'm more into the piezo one with two piezo at 90 degrés. Just to be sure, you put one on the X axis and Y axis and then play with the gpio interrupt ? I don't understand the fact that you need only two elements to get my 4 directions . Could you explain a bit more ?

Thanks for the first reply btw !

Gronjus

[Gavinmc42]

Piezo's vibrate when hit and generate AC voltages.
If hit one way it will generate a positive first spike, hit from other direction it will be negative.
One sensor can be used to trigger two bipolar transistors if the base voltage gets above 0.6 volts.
By capacitor coupling and rectifying the piezo output you can drive two transistors.
Which one causes the GPIO interrupt first is the direction it was hit.

Not sure exact circuit because extra rectifier diode drops decrease sensitivity.

Resistor bias at 3v3/2 and capacitor couple to PNP and NPN transistors.
If first shock goes low ie 3V3 -0.6V then PNP is triggered first, else positive shock 0V+0.6V then NPN is triggered first.

Old piezo buzzer element can be used too, fix one edge, solder or screw nuts/bolt to other free side.
You can use hall effect sensors too if you suspend a magnet via springs.
I have seen seismic sensors made from speaker cones with weights on them.
The trick it to make them less sensitive to vibration and only shock.
Even optosensors with moving barrier breaking the light....