Normal House Wiring Diagram - Basic Electricity Tutorial Primarily About Switches. Single Pole Double Throw Switches. Diagram 3 makes use of the Single Pole Double Throw Switch. The common terminal is the middle terminal in the SPDT Knife Switch or if you are using a household switch, it would be the brass colored terminal.. This LDR circuit diagram shows how you can make a light detector. An LDR or “Light Dependent Resistor” is a resistor where the resistance decreases with the strength of the light..