I am not so sure what objects are you detecting and 
what is the requirement. The property of the object
and the background can affect the design by a lot.

What do you mean by "20-100ft with 1ft accuracy"? 
Do you mean that you want to detect objects between 
20-100ft and maybe 19 to 101ft are okay? Or do you 
mean that you want to detect an object in adjustable
x +/-1 foot with 20<=x<=100? The 2nd explanation may
be harder to achieve.  

There are some optics sensors called convergent beam 
sensors or fixed focus background suppression sensors 
which only detect certain ranges. They have "cross eyes" 
between the emitter and receiver light path so that only 
the crossed region will be detected. Most convergent beam 
sensors use a lens system that focuses the emitted light 
to an exact point in front of the sensor, and focuses the 
receiver element at the same point. This design produces 
a small, intense, and well-defined sensing area at a fixed 
distance from the sensor lens.

However normally the sensing distance is much lower. A 
laser emitter based convergent beam sensor might be possible 
to achieve the sensing distance. 

Regards,
Xiaofan

-----Original Message-----
From: Jake Brownson [mailto:jbrownson@gmail.com]
Sent: Friday, September 30, 2005 3:19 PM
To: piclist@mit.edu
Subject: [EE] Long distance range finder


I'm researching a project, and am having difficulty finding one major
component required. I need to be able to find distances between
20-100ft or so with maybe 1ft accuracy. Is there anything out there
that comes anything close to this? I've seen laser range finder
products available, but I haven't found any sensor modules. I suppose
getting a complete system and pulling it apart would be an option, but
I thought I'd ask the list.

Thanks for any suggestions,

~Jake B

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