It’s the middle of the night, when suddenly you’re jarred awake by your ringing phone. It must be urgent, so you can’t waste time—or worse, miss the call—fumbling around trying to find the receiver. Instead, simply touch your hand to the top of your bedside table to answer the speakerphone. The secret is a stud finder (stuffed into the drawer of the nightstand). With a few modifications, it can sense when your hand is near it and activate a switch connected to your landline. You can use versions of the system to connect other appliances like lamps and air conditioners and control them by touch as well. It’s the next best thing to having night vision.
Time: 2 hours
1. Open the stud finder’s [A] battery compartment and remove the door and guide. Solder the power-supply wires to the battery tabs.
2. Wrap a wire to one of the relay’s [B] coil terminals. Wrap wires to both sides of a photoresistor, and connect one of them to the other coil terminal on the relay.
3. Solder the unattached ends of the wires from the relay and the photoresistor to the stud finder.
4. Solder wires to the contact terminals of the relay. Attach the photoresistor to the upper red LED.
5. To enable the phone to receive info from the stud finder, solder wires to the phone’s speaker-button pins. Drill a hole in the phone, insert the wires through it, and crimp them into the battery-pack connector.
6. Drill a hole in the back of your night table, and stick the stud finder in the drawer. Attach the phone to the stud finder’s battery-pack connector terminals.
Five amazing, clean technologies that will set us free, in this month's energy-focused issue. Also: how to build a better bomb detector, the robotic toys that are raising your children, a human catapult, the world's smallest arcade, and much more.