Science Buddies: "Ask an Expert"

Materials:
1 shoe box
2 cardboard "room" dividers
4 min holiday lights
12-16 brad fasteners
5-6 paper clips
2 D-Cell batteries
Enough wire to go around box two times (CAT3 phone cable)

Directions:
Slit the two cardboard room dividers half way through in the middle and slide them together to make a + that fits inside the box and divides the box into four room.s Wire the four rooms in parallel. Each room should have a working light with a switch inside the room. ONe of the rooms must have 2 three-way switches enabling the light to be turned on and off from opposite sides of the room. All lights should be powered by the d-cell batteries. Switches are made up of the paper clips and brass brads.

I have done the following BUT i need to work on the 2 three way switches!

HELP!

Mmadison - Looks like the novelty of the project is how the 3-way or 2-way switches control of the light in one room. When you say the rooms are wired in parallel, it is partially true (at least from a voltage standpoint) with the three rooms each having a single pole, single throw (SPST) switch. The fourth room must have two single pole, double throw (SPDT) switches wired so that either switch turns the light off or on. See the attached diagram for the basic circuit. Two 1.5V 'D' Cells in series is about right (a little high for standard Holiday lights usually on a string of 100). Do you know why the string of lights works on 120 Volts AC in the string but on about 2.4 volts DC when using the battery? You might be able to explain the series versus parallel wiring in your demonstration.

Rick Marz

Hi mmadison,

Additional resources are at http://www.wiringhelp.com/electrical/el ... witch.html

This page has two videos on how to install 3-way switches, in addition to wiring diagrams.