hallway person detector

I need a way to detect a person walking through a hallway. It is for a lighting project and I only have access to one side of the hall for
components. What kind of sensor would be the cheapest to install? The hall is about 3 feet wide and I just need to know when a person is in a 1 or 2 foot section of the hall. I don't want a device that makes any noise or uses visible light. How well would bouncing infrared off the opposite semi gloss painted wall and look for the signal to go away to be the trigger work? Anyone try something like this? Any ideas would be greatly appreciated.
By the way it will be connected to a microcontroller that has an analog input (incase this increases my options).
Alan
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email address abparekh2002 at hotmail.com
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Think "passive infrared detector"
<http://www.google.com/search?hl=en&ie=UTF-8&oe=UTF-8&q=passive+infrared+detector&spell=1
A.P. wrote:

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http://www.mpja.com/productview.asp?productx60+KT
PIR module with only 3 connections. Dual element detector element designed for human body detection. 5-10VDC input power. Active high output with a pulse width of approx. .5 Sec. (remains active as long as there is motion). Detects motion up to 10ft. Add a small relay to interface to higher power loads.
Stock No.: 7860 KT Price: $ 9.95
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I *VERY* much hope you're not the same guy who wants to build an electronically fired pistol, posting under a false name!
;-)
Tom

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hahahaha :-)
Refa

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lol, no I am not but I would love to see a burglar steal anything from his house if he combines the two ideas.

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hall
semi
For a hallway 3 feet wide, a GP2D12 sensor would work pretty well. you can get them fairly cheaply at www.arrow.com for less than $10.
They are 3 wire, 5V devices, have their own regulator, and will put out a voltage between about .3V and 3V which is roughly proportional to the distance. The GP2D12 works up to about 80cm (actually, a bit more), and the GP2D120 works up to 10 cm (again, a bit more). They also have one that will output the distance data as a digital bitstream for the A/D challenged.
I just built a hallway sensor using one for an automatic light. It uses a PIC to keep the light on for 3 minutes.
Regards, Bob Monsen
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2
er, inversely proportional... at 80cm, the output is .3, and at about 2 cm, the outputs is 3V.

the
will
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