Since spring has almost arrived, I wanted to check how many birds are still coming to my feeder before removing it from the balcony. Good to have a Raspberry Pi for counting our feathered friends!
There are several ways to detect motion with a Raspberry Pi. The best and most popular method is connecting a PIR sensor, which detects the infrared radiation emitted or reflected from an object. Motion can be also detected by image processing of webcam frames with a software called motion. However, image processing requires CPU power, which is limited on a Raspberry Pi. Furthermore, motion detection with a webcam depends on decent light-conditions and may be triggered from inanimate objects, such as trees or leaves moved by the wind.
Here I wanted to test whether it is possible to count bird visits using an infrared light barrier. I had both a photo diode and a high power infrared LED lying around in my tool box (SFH230-FA and SFH4550). Consider this project as a “proof-of-principle” build and be aware that there are more reliable ways for detecting motion!
Since the SFH4550 has a narrow emission angle of 3°, I designed a circuit which allows to sense the light reflected by an obstacle which moves into the IR beam. The setup is very similar to IR range sensors used in robotics. The detection range is about 30 cm, which is decent to monitor the space within the bird feeder. Furthermore, the diodes are about 0.64 € each, which is much cheaper than a ready-to-use IR distance shield.