Hi Russell,
On this little application of mine I will have a TX attached to a
person, transmitting a 250uS pulse every 250mS. This pulse is generated
by a uC(to allow for flexibility, could have used a couple of 555). The
IR TX diodes(I am using two at the moment in parallel) is the SFH 415-U
from Siemens and I am driving them with 1A each to increase IR output.

The receiver, will be mounted on a vehicle,  I am using three BPV11F
from Vishay in parallel to detect the IR. Since connecting the three in
parallel I got about 200mV @ about 2m distance. My idea is, after
conditioning the signal (amplify it and also limiting it), to feed it
into an ADC. 
The micro I am using (HC08) can convert at about 20uS if I divide the
signal received in 20uS slices I can then measure the signal received.
I am not looking for accurate measurement of distance, this is not a
range finder, I am just looking for a sort of level. Maybe this is a bit
ambitious, but it's just an idea in my head that I want to try out.
I will have three to four of these detectors which will also let me know
from which area the IR is coming from by telling me which detector as
the highest level of IR... it all makes sense in my head...
I would prefer to use RF directional detection but the learning curve at
the moment is to high(to many things going on) so IR seamed the next
solution.
Maybe I am wrong...
So the idea is, vehicle will head on the direction of the person by
following IR but will be able to detect if it is close enough and stop,
if person starts moving towards it will detect increased level of IR and
will reverse out of the way.
I am open to other suggestions on how to do this; in essence I need to
detect direction where the TX is and sort of distance from it (low
accuracy).
Best regards
		Luis

P.S- hope you understand what I mean, after reading this even I am
confused :) 

 



-----Original Message-----
From: piclist-bounces@mit.edu [mailto:piclist-bounces@mit.edu] On Behalf
Of Russell McMahon
Sent: 26 June 2006 14:35
To: Microcontroller discussion list - Public.
Subject: Re: [EE] IR photodiode or phototransistor

> ... I need to be able to measure signal magnitude to let me know if
> I am close or far from the TX.

That should probably read "... I intend to measure signal magnitude in 
the hope that it will let me know if  I am close or far from the TX.".

Then either :-) or :-( depending on how Murphy is feeling in your 
application.
In the absence of 'confounding' inputs light level is proportional to 
the inverse square of distance - no problem. In the real world you are 
liable to have 'quite some fun' picking out the signal of interest. 
I'd be extremely interested in how you intend to do this and in what 
sort of result you achieve. It *sounds* simple enough :-). Short range 
range detection by simple techniques is an often sought after 
objective and I don't recall seeing one that successfully used optical 
signal amplitude - which is not to say that it's not achievable. Are 
you able to tell us more about the application?


            Russell


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