Motion Sensor for moving cars

Thread Starter

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?
 

iONic

Joined Nov 16, 2007
1,650
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.
 

Thread Starter

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
22,220
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?

There are some pretty cool designs for driver-less cars out there thanks to DARPAs $1 million reward (detail on wiki).

Could you explain the full project a little more clearly than "detect a passing car 15-20mph", such as location of sensor, 15-20mph relative to what, what is defined as passing, etc?
 

hgmjr

Joined Jan 28, 2005
9,029
I have been quite impressed with the performance of a driveway alarm that I purchased and installed a couple of years back. It uses a magnetic pickup along with interface circuit and a simple battery powered wireless transmitter. It does a darn good job of detecting the vehicle traffic that passes my driveway at 20 to 30 mph even though it is easily 10 feet away from the road.

The device can be seen at www.mightymule.com. It is their driveway alarm product.

hgmjr

FIXED my typo in the URL per Sgtwookie's comment....
 
Last edited:

John P

Joined Oct 14, 2008
1,839
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.
Well well, look what's on the Sparkfun site:
http://www.sparkfun.com/news/726
Title: "Laser Tape Measure Hacking Challenge", dated 2011.11.07
 

SgtWookie

Joined Jul 17, 2007
22,220
Hmm, I had no idea they were having a laser tape hacking challenge.

Anyway, that laser I mentioned is too expensive for a project like this, and the risk factor is just too high.

Hgmjr's post jostled my memory a bit; I'd seen a Vehicle Loop Detector earlier this year and had thrown it in a simulation; here's a link to the project description:
http://www3.telus.net/chemelec/Projects/Loop-Detector/Loop-Detector.htm

And here's the schematic:



As far as the loop, what he's written on the schematic is 4 turns of wire in a 6' diameter loop; that calculates out to roughly 64uH; you'd need just under 76 feet of wire for such a loop. Even if you go to Radio Shack, that much wire will only run you around $7. It doesn't have to be any particular type of wire, either.
 
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