PIR sensors, weatherproofing

[AllyCat]

Hi,

You are way above me.

Perhaps, because what you appear to be attempting is probably quite (or even very) "difficult".

However, I don't recall a proper "specification" in this thread, so far. What type of birds*, e.g. size and colour, etc.? At what range do you wish to detect them and with what "field of view", i.e. the required acceptance (or rejection) angles of detection from the sensor?

There are various possible detection methods such as: PIR, Doppler "Radar", Doppler Ultrasonics or Visible (simple "image" recognition), etc.. If the birds have high optical contrast (e.g. against a light sky) then an optical method might be the most successful. Otherwise, I would consider Ultrasonic Doppler, using a reflector (possibly something like a small saucepan lid, but that can be calculated later) to define the detection beam width and range.

If my "back of envelope" calculations are correct, Doppler Ultrasonics and Radar are quite similar, but I think a bird may reflect more sound than electromagnetic energy back to a sensor (and IMHO 40 kHz sound is probably more "understandable" than 10.5 GHz electromagnetic waves). In both cases the wavelength is about 1 inch: 10.5 GHz at the speed of light (300,000 km/sec) gives a wavelength of 2.8 cms, 40 kHz at the speed of sound (~1,000 m/sec) gives 2.5 cms. Thus an object moving at 1 metre/sec (say 2mph, or slow walking pace) will create a doppler shift (frequency) of about 75 Hz (2 x 37.5, because both the "transmit" and "receive" distances are being shortened or extended).

So, if you can identify the speed of a typical bird (and/or its wings), it may be possible to devise a suitable (bandpass) audio filter (or maybe more than one) to allow the PICaxe to discrimate between birds and other (interference) moving objects. Not easy, but an interesting challenge. And even if it fails, the "bleeps" from an ultrasonic transducer might scare the birds away.

*EDIT: Ah, looking back I see it's pidgeons. Wood or Common?

Cheers, Alan.

 

[Dippy]

I'd think that any ultrasonics could be upset by wind up your hole but I'm definitely not saying impossible.
Depending on your repelling method false triggers may not be a real problem.

I have done Doppler microwave (not radar per se) measurements and experimented with FFT on PIC and dsPIC (vehicle speed).
The maths involved for FFT is likely beyond PICAXE if you want real accuracy but I would suggest that an 'any signal' response wouldn't be difficult to process. And ditto for simple analogue gain+filtering methods using op-amps.
FYI I used microwave products made by http://www.microwave-solutions.com
Not cheap but performance was flawless.

The big advantage with microwave is that your shielding (assuming a degree of common sense) doesn't have to be fussy and the angle of dangle can be wide.

If you can't get circuits or precise advice the development time may be considerable.
I would experiment with U/S or PIR ready-made modules before diving into microwave.

PS. Is a 'pidgeon' different from a 'pigeon'?

 

[beb101]

Maybe a simple sound generator and as has been suggested, a shotgun.

Reference:
http://digitalcommons.unl.edu/cgi/viewcontent.cgi?article=1076&context=icwdm_usdanwrc

Summary quotes:
Acoustic frequency
==================
"Pigeons are most sensitive to sound between 1 - 2
kHz, with an absolute upper limit of about 10 kHz
(Goerdel-Leich and Schwartzkopff 1984). None of the
avian species that have been examined has shown
sensitivity to frequencies above 20 kHz (ultrasound)
(Schwartzkopff 1973) and generally the upper threshold
is about 10 kHz (Hamershock 1992, Necker 2000)."

Conclusion:
===========
"By themselves, acoustic devices are ineffective or
effective only for a short time at dispersing birds. To be
useful, acoustic devices must be combined with other
control techniques in an integrated management program.
The most effective use of acoustic signals is when they
are reinforced with activities that produce death or a
painful experience to some members of the population.
Such reinforcement will prevent birds from habituating to
the auditory stimulus."