Both a touch and a contact switch are built onto one PC board so that the builder can see how each works. A battery can power the contact switch but youÆll need an AC power supply for the touch switch to work well (use No. 80-040) for reasons explained with the kit. (The circuit is triggered by AC "hum" ; so use a wall wart power supply for best result.) The circuit switches a relay with a 3 amp; 110 volt rating. Use to switch lamps; other appliances.