title: how to use accelerometer sensor to detect and match two toy cars' collision
body: <p>I am using Accelerometer Sensor to collect a toy car's acceleration data to tell whether it bumps into something or collide with another toy car. My idea is checking whether there is a sharp change of its acceleration data (for simplicity, just considering its x and y axis acceleration data since it is a toy car running on a smooth ground). But when the car is started from stop, there is also a dramatic change with its acceleration data. So I need to distinguish them. Based on my instinct, bumping will cause a sharp changed acceleration in short time, while engine starting will cause a smooth changed acceleration data. 
  I think this should be a quite common question. But I am a really new hand. So I'd like to know whether there is an algorithm or method to distinguish them. It would be great if there is an implementation in C. 
  Thanks a lot.</p>
  
  <p>[update the bumping situations]<br>
  Let me make my question more specific. My project involves several toy cars, they can bump into each other, or bump to other things(such as walls). What I need to do is to find out which two cars are collided into each other. My idea is to try to compare two cars' acceleration data to see if they are matched with the same pattern. I divided this project into several steps:<br>
  1. detect bumps, so I need to distinguish the car bumping into something from being started or some other situations, such as jolts on the road.<br>
  2. match two cars' bump features to see if they are bumped into each other. What kind of features can I use?<br>
  <br>
  [update] <br>
  <br> I found this url containing very useful information for peak finding.<br>
  <a href="http://terpconnect.umd.edu/~toh/spectrum/PeakFindingandMeasurement.htm" rel="nofollow">http://terpconnect.umd.edu/~toh/spectrum/PeakFindingandMeasurement.htm</a></p>