long range sensing

Hi, Im trying to sense if there is an object at 100m ? can infrared do it or ultrasound ??

ahmedragia21 said:

Hi, Im trying to sense if there is an object at 100m ? can infrared do it or ultrasound ??

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Whats the object, animal, mineral or vegetable.?

human or animal

How would it be focused?

just like that O -------------------X <-- object
i really wanna do it to detect a human passing near that sensor then do an alarm

A couple of meters maybe, but unless your sensor has a narrow field of view and decent aim 100m is pretty far.

yea im looking for a sensor like that ...

any ideas ?

Well some military have long range IR detection systems that have that kind of range but I'm sure it's not something easy or affordable.

Lefty

hmm, so i wont do it ?

ahmedragia21 said:

hmm, so i wont do it ?

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That's up to you. Me, I would just get a dog.

Lefty

hehe , really a nice soultion , but would you help me to find an electric solution ?

The only solution I've found for something like that (and believe me I've looked long and hard) that isn't more than $5K is the

Opti-Logic RS100 Industrial Laser Range Finder w/ RS232 Serial Computer Data Interface Ports w/ FREE UPS

and it's variations. It still costs $500 though. It's also not terribly accurate...1% of 100m is still 1m which makes it useless up close. It can only see large targets due it's field of view (don't expect to be able to light up a point like with a laser pointer and find out how far it is...that takes one of the $5000+ models).

100m is too far for ultrasonic or infrared. Pretty much only laser and radar will do it.

If you want to make a beam breaker though...that's easy. Just use a laser pointer and a sensor opposite of it. But you need something on both sides.

yea thanks ! i were about to show you the thread , i really wanted to hear your opinion ..
well how about this kit
**broken link removed**
can it does the job ?
but i really dont know how long it can sense the vibrations of feet of a human ?

It's cheap enough to experiment with. I would think cars on the road might interfere with it though. But I doubt it works more than a few meters (definately not 100m). There's just too much noise.

Unfortuantely , the kit you showed me later , is only 0.2 m ...
so its not really possible to do this thing ? im really wondering

The problem with the laser idea , is it can be seen by the thief , so its not really a good idea ...
Would you explain it more ?

ahmedragia21 said:

just like that O -------------------X <-- object
i really wanna do it to detect a human passing near that sensor then do an alarm

Click to expand...

You could try a laser pointer with a remote 2.5cm prism, detect loss of return beam.
That is an interrupted laser pointer beam.

ahmedragia21 said:

Hi, Im trying to sense if there is an object at 100m ? can infrared do it or ultrasound ??

Click to expand...

Consider this:
You have two telescopes of some sort ... maybe spotting scopes .... probably whatever you can afford. Each scope is placed on a line several meters apart, and sighted in on the target .... 100 meters away. When you have sighted and focused each scope on the target, you remove, affix, ... or somehow place ... a phototransistor or some other optically sensitive IC at the focus point of each telescope. .... You might describe this as a 'parallax' method. The final step would be to enable an AND logic gate to alert you when both scopes had sensed the same target at the same time.

The success of this method would depend on whether you could get the target object to create enough of a contrast signal in the phototransistors to switch logic states.....
Some additional improvisation and testing might be necessary... not certain how far apart the two scopes would have to be separated.
You wouldn't want to have a false positive .... if an object nearer than the target was lengthy enough to trigger the alarm.

A Charge Coupled Device type of sensor, as used in cameras or astronomy, might have a better chance of providing a signal indicating that the target is
present. However, a CCD would require a more complicated interface circuit.