The sensor activates upon detecting your hand or rubbish, triggering the stepper motor that then pushes the lid up automatically. The motor closes the lid after 5 seconds. The second sensor inside the bin activates the LED and speaker when the bin is at capacity.
The intention behind this is to force the person who threw the last piece of rubbish to take out the bin.
The image to the right is a photo of the working physical model.
The images below are renders of the 3D CAD.