Break-Beam IR Detector?

Jaggermax

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Just interested to know if any of you have ever tried to use a break-beam type of triggering device instead of a PIR.  Years ago in collage, I designed a IR beam transmitter and receiver that would work over 200 feet away.  For the tranmsitter, I used a small maglite, replaced the bulb with an IR diode and added a simple 555 timer based pulse width oscillator to pulse the output to save power and eliminate false alarms such as birds and falling leaves.  The receiver had an LED that would turn off when the receiver detected the IR pulse from the emitter.  The IR receiver was also 555 timer based and was tuned to the same 44kHz pulse frequency of the emitter.  I had a pot. which adjusted how long the beam had to be broken to trigger the counter.  To set it up, you simply place the emitter box on a strudy tree and aimed the maglite at a parabolic dish on the reciever in which the IR transistor was located.  It worked great, the only problem was that it went through the 9 volt batteries to quickly.  I am going to build another trail cam for using this same circuit and higher amp/hour batteries and will let you all know how it goes.  The benifit of the break-beam design is that you can set it to whatever height you want to detect such as deer eliminate the smaller animals like rabbits, squirrels, etc... .  It also can have much longer range.  
 



Archilochus

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Hi Jaggermax,
I've been fiddling around with some very similar circuits.  Thinking of trying to make a "hummingbird detector" (swiches or PIRs didn't work).  I did build an active IR "break-beam" detector with a range of about 90 feet, but found that to be way too much for photography purposes since something breaking the beam at 90 feet away would be almost invisible in the pic. It also ate up the batts fast!  I ended up reducing this circuits range to about 15 feet and using it as a visitor counter at a Nature Conservancy preserve.  Still eats up the batts!

To reduce average power consumption, I've been thinking of using "tone-bursts" of modulated IR - Say around 50 cycles at 36KHz, 2 "bursts" per second with a 10% or less duty cycle - rather than contiuously emitting the 36 KHz "tone".   The transmitter side is fairly simple, but the receiver / demodulator presents some headaches.  I'll post any reliable circuits that I might come up with.

I used some Trail-Master active IR "break-beam" detectors several years back.  While they did allow for very accurate detection areas and discrimination of smaller animals, they also had a few negatives.  Battery life was high on the "negative" side, as was the difficulty of set up - they had a VERY narrow field of view and had to be carefully aligned.  Any animal rubbing against, climbing over or otherwise touhing the emitter or detector would throw it out of alignment.  This was made worse by the really cheap straps and brackets that Trail-Master uses to fasten the units to trees.  Also, if an item like a leaf or branch fell in the "beam", it would disable the system, preventing more pics from being taken - not a problem with passive IR detectors.  If you did want to capture small animals on film, the powerful IR beam (capable of a 90 foot+ detection distance) would sometimes reflect around the animal if IR reflective surfaces were nearby.

Archilochus
 

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