# Motion Sensor for moving cars

#### LightAce

Joined Sep 19, 2010
6
My group and I are trying to figure out which motion sensor would be best capable of detecting a passing car moving at least 15-20mph. We were thinking PIR however it usually takes about 1.8 seconds for it to detect movement which is too long for a car moving at that speed.

What would be the best motion sensor for this application?

#### John P

Joined Oct 14, 2008
1,914
Uh oh. Are you on the same side as the people behind this other thread, or are you competitors?

I'm not too happy with a college design course that becomes a contest in who can get the best advice off Internet discussion groups. And I'd bet the prof wouldn't be either!

#### iONic

Joined Nov 16, 2007
1,654
Time for some research. You can still use the internet and arrive at an answer, but you have to use your noggen. Start reading Datasheets!

#### jbord39

Joined Mar 31, 2010
41
Since when is asking knowledgable people about a good direction not research? Anyway I am guessing we are the same group or going to different colleges.

#### LightAce

Joined Sep 19, 2010
6
I don't think we go to the same college. I have been looking at ultrasonic sensors like those used in radar guns but not sure if that's the most straightforward way of going about this. I just need help on moving in the right direction

#### SgtWookie

Joined Jul 17, 2007
22,221
Actually, radar guns were using KU-band pulse doppler radar; 18GHz range. They used to use X-band (9GHz) back in the 70's and 80's.

Now there's LIDAR/LADAR, which makes it more difficult for motorists to detect their use.

Stanley came out with a level that has a built-in laser "tape measure", good to within 1/4" at 100 feet. I can't help but wonder if that could be a candidate for hacking.

#### thatoneguy

Joined Feb 19, 2009
6,359
My group and I are trying to figure out which motion sensor would be best capable of detecting a passing car moving at least 15-20mph. We were thinking PIR however it usually takes about 1.8 seconds for it to detect movement which is too long for a car moving at that speed.

What would be the best motion sensor for this application?
Detecting a passing car, from what perspective? The car being passed, or from a bridge to see if two cars are moving in the same direction, with one moving faster than the other?