Nest Box Technology

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electronic prototype boardThat's how it looks like under the roof behind the plexiglass of my Great Tit Nest Box: a little b&w camera and an electronic prototype board are fixed here. You can see the infrared light emitting diodes (IR-LEDs) around the camera lens, that's why the box is always as bright as daylight. Besides, that's the reason why I didn't use a color camera, I would have been forced to use normal light, visible for the birds. IR light doesn't disturb them. I made sure in asking that in a science radio magazin where the ornithologist Prof. Peter Berthold from Vogelwarte Radolfzell stated, that birds do not notice the IR light and so it is first choice for bird watching.
Recorded radio interview from 1997:  

view from nest box bottomview from nest box frontThe pictures on the left side show how the electronics are attached to the box which is opened on the front and bottom. Behind the acrylic glass an electret microfon catches the sound through a little hole. Hidden in the wooden pieces on the front side are the receiver and the transmitter for one of the two infrared light barriers. On the same height in the inside is the second one, so can detect the flight direction of the bird. The IR transmitter diodes are pulsed with approx. 40 kHz, the receiver locks on this frequency - you get a high "signal-to-noise ratio" against sunlight or other light sources.
Plug in the side wallNow you know some of the electronic parts, the others are for voltage regulation, microphone amplifier and sensor buffers. And I added a temperature sensor which can be easily evaluated by a 3-wire protocol.
From the double-row plug all signals get to the 10-pin plug in the side wall and finally a long wire leads into the house for evaluation of the signals. For this fun one has to drill one or three long holes...

Electronic Circuit

electronic circuitThe IR transmitter diodes are pulsed with about 40 kHz, driven by the NE555, connected as astable multivibrator. To conserve power, the duty cycle is approx. 1:5. The receivers are very sensitiv, so the high resitor value in series with the IR diodes is fully sufficient. These are ready IR receivers tuned to this frequency with filtered outputs. This provides least sensitivity otherwise the sunlight could interfer the signal. The outputs are buffered with LS gates so the signals will make the 10m distance without errors - OK, one could do this better...
Around the Double Op-Amp NE5532 I've built two sensitive microphone amplifiers to catch the sound in and in front of the nest box. The wanted signal becomes gets line level to ensure optimum sound on the distant TV or VCR.
The power supply is trivial: three integrated voltage regulators provide 12V for the b&w camera and the IR illumination, 10V for the amplifier (value can differ) and 5V for the logic part.
At last I mounted a temperature sensor DS1620 into the nest box, a little apart off the elektronics. The evaluation of temperature and both light barriers is done by a little microcomputer: this offers you unlimited options...
nest box Now you see how the nest box is hanging in the birch-tree, the flight hole looks to the eastern direction and is waiting for the Great Tits...
The cable climbs hand over hand through the trees and suvrived some winters without damage.
nest box in the tree

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updated: 2020-11-08