Speed trap

Author: Dave
Date: 11.17.12 - 7:54am

So, the other day as I was pulling out of my driveway, just as I got it in gear to go forward, I was passed by some asshat going about 80mph. Seeing how its a 30mph residential neighborhood with plenty of kids and is a no passing zone I was a little pissed off, but couldnt even catch up to try to get his plate.

This got me thinking and doing a little research. Below is some initial thoughts on how to construct a speed camera for home use that should not require any real hardware modifications to commercial components.

  1. Buy a radar gun with lcd readout (85 dollars on amazon)
  2. hard mount a web cam behind lcd screen to process image output and convert to numeric input
  3. custom PC software to process lcd image, if speed is greater than limit,record the date and time to a database along with the speed and raw image and use a second web cam to take a picture of the car and plate.
The only real mod to the radar gun will be a piece of tape to lock the trigger on, and a power adapter so I can plug it into a wall power source instead of using internal batteries. Even I can do that..

The software to convert the lcd image to numeric input should actually be quite easy. You will not need a full blown OCR library for this. The reader camera will be hard mounted to a fixed display and the lcd output is entirely predictable in its limited output variations. basically you can just compare if a specific block of the image is black or not to know if a segment is on or not. This will be very fast and highly accurate with minimal code. I will probably put the gun and camera in a box with its own light source for consistency.

The only concern I can think of right now is will the image capture be able to be triggered fast enough to catch a speeding car in the vision window I will have from the cameras vantage point. And how to best tune the capture angle so it works with traffic going in both directions. I supposed I could continiously buffer 3 seconds of a video stream and extract the whole event from there. Will have to see whats required as I dont have any experience in this area. Should be fun anyway :)

Of course a nice web interface with sms alerts and graphing will follow..

edit 4.3.16 - Just found a post on hackaday for a raspberry pi as speed camera

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