We have a bird nest box close to our terrace which has been used by a Great Tit (Parus major) couple during the recent years and we hope to have them back breeding this year. However, the box is in a bad condition and hast to be replaced sooner or later. As a scientist I couldn't resist having a box with a counter measuring the activity of the birds at their nest. Although it is located close to our house, I would not like to have a cable connected to the counter and thus decided on a battery powered device. As I do not want to disturb breeding, the device has to run on a single pack of batteries throughout the season and thus has to be limited in power drain. So it's an ATTiny85 processor instead or a full grown ARDUINO.
I thought of a method to switch the display on and off without going too close to the box - that is where the laser comes into play...
The video shows the box in action. The rightmost LED shows when the lightbarrier was triggerd. The LEDs have different colors with different colors and position representing different digits. When the laser hits the sensor all LEDs blink three times indicating that the actual number of visits will be shown shortly. Each of the first five LEDs represents a digit, so 99999 visits can be counted. In the video you see LED 3 blinking once, LED 4 blinking twice and LED 5 blinking four times - that is 124 visits.
For parts list see Appendix (Step 7)