Bonus Lesson -- Entrance counter, single-sided, dual sensor

This lesson presents an improved version of the entrance counter from lesson 15. While that version used a DIY approach using solely parts from the original Grandpa's Gizmos course, it had the disadvantage of needing to run a lot of wire to have the light source on the opposite side of the door from the sensor. This new version presents two different sensors that can be used to keep everything on one side of the door.