People detecting

[Bern]

I need a way to detect people approaching. Thinking about using ultra-sonics, something similar to the way Polaroid used to do their camera focusing. Need to detect them at about twenty-five feet, and less. Any suggestions on transducers that can do the job, at the best price? (Need lots of them) IR sensors will sort of work, but they do not tell me the difference between coming and going. Any suggestions on where might be a better place to look? I did some digging around in some robot forums, but did not come up with anything usable. Thanks for all help!!!

[dyarker]

Two IR beams 2 to 5 inches apart can tell direction, and probably still cheaper than ultrasonic. (which ever beam is broken first is the from direction)

[jwax]

A $20 motion detector from HomeDepot will do the detecting. Now if you want to detect "coming vs. going", that's something altogether different!
Ultrasonics may be the best for that, as in a sonar ranger to determine an increasing distance vs. a decreasing distance.

[Bern]

The targets (people) will be approaching the sensing units. They will not be crossing a beam or beams. That is the catch. -- Jwax you have the idea. I don’t see any problem in processing the data, once I have it, but getting cheap sensors that provide the inputs is where my questions lie.

[Sambuchi]

Hey bern

i read your problem...

this is not hard to do if all you want is something that will tell you that...

You have a "thing" infront of you and want to know if that thing is moving closer or farther away.

ultra-sonics is one answer but can be expensive.

dyarker mentioned a way with IR but there is another way using IR that could work... you could build your own IR Proximity sensor.

I'll let you look at this example to save some time explaining..


http://users.skynet.be/peter.smolders/l ... sensor.htm

Good luck

[Appalacious]

these ultrasonic sensors have a range of 3cm-4m (1in.-13ft) and they're $25.00.

http://www.acroname.com/robotics/parts/R271-SRF05.html

[Ken10]

Hi Bern,
I've used these ultrasonic sensors. They have a range from 0 to 254 inches, with a 1 inch resolution. Pulse width, analog, and serial outputs in a small package. This guy did a really nice job on the design.
Hope this helps.
Regards,
Ken
http://www.maxbotix.com/

[JohnDay]

Backin the 70's I designed some ultrasonic motion detectors for the security industry. They are probably still the most reliable way of detecting people- particularly as you can (if you want) readily remove the effects of things like curtains blowing and pets running around.

The 40kHz sensors used by Devantech (and sold by Acroname) are pretty easy tog et. Last ones I got cost me 11c each for a batch of 1000 of each of transmitter and receiver on eBay about 3 months ago.

John