The servo motor turns back and forth. If something comes within 40cm of the beam, then the servo motor stops, the on-board buzzer starts to beep, and the LCD reads “OBJECT DETECTED”.

Making a servo tester using an Attiny85 micro chip, Attiny45 also works for this project. This diy servo tester is as good as ...

To that end, it uses an Arduino Nano armed with an ultrasonic distance sensor to detect when mice have entered a plastic container. The container’s hinged door is is held open with a servo.