My roommate is a very considerate person, yet he has a habit of leaving our room door open when he goes to the common room. To be frank, I don’t mind open doors in the daytime. But since I am a light sleeper and get awaken by the slightest rise in light or sound intensity, my roommate’s trips to the common area in the nighttime disrupt my sleep. This is why my first class assignment for Intro to IM features a switch that turns on the LED when the door gets open.
The switch I made is normally closed and connected in parallel to the LED.
When the door is closed, electricity flows through the closed switch (following the path of least resistance). When the door is open, however, the switch is open as well and electricity now passes through the only other route available – through the LED. The lit up LED then serves as a reminder to my roommate to close the door behind him.
To make the switch, I first got two wooden sticks and taped some copper tape on each of them. I then took a wire, soldered its one end onto the copper tape and connected the other end to the breadboard. Once both contacts of the switch were connected to the breadboard, I taped the two wooden sticks on the room door so that the two pieces of copper tape were in contact with each other.
When the door gets open the sticks move apart and the LED lights up. Upon seeing that, my roommate closes the door and I get a good night’s rest.