A battery-operated switch offers an easy introduction to circuit-building and DC electricity concepts. A switch is a mechanical device that operates an electrical contact. When the contact is open, no current flows. Closing the contact completes the circuit, allowing current to run a motor, light or other component. The low voltages produced by household batteries make these types of circuits safe for beginning hobbyists. An elementary circuit such as this typically takes less than 15 minutes to build. You can find all the necessary parts at a local electronics store such as Radio Shack.
Plug the soldering iron into an electrical outlet and give it a few minutes to reach operating temperature.
Cut a 5-inch length of 22-gauge stranded wire and strip about 1/2 inch of insulation from both ends. Twist the wire strands at each end so they make a tight, neat bundle.
Test the soldering iron by touching the tip to the end of the solder. If the solder melts quickly, the iron is ready.
Touch the metal end of the wire with the soldering iron. After a few seconds, touch the solder to the wire; it should melt and flow into the wire strands. Use only enough solder to coat the wire; avoid blobs. Do the same for the other end of the wire. Let the wire cool for a moment.
Bend the ends of the wire into hook shapes using your long-nosed pliers. Slip one end through one of the switch's solder lugs. Crimp the wire to the lug with the pliers.
Slip the end of the battery clip's red wire through the other solder lug and crimp it with the pliers. Touch the soldering iron to one lug and melt some solder onto it and the wire, coating both. Solder the other lug in the same manner.
Snap a 9-volt battery into the clip.
Turn on the multimeter and set it to read DC volts. Touch the meter's probe tips to the free end of the prepared wire and the black battery wire. Flip the switch on and off. You should see a voltage reading of zero on the meter when the switch is off and about 9 volts when it's on.
Connect the black battery wire to your device. If your device has negative and positive power terminals, connect the black wire to the negative terminal; otherwise, the polarity doesn't matter. Connect the free end of the prepared wire to the device's other power terminal. Solder both connections. Flip the switch on and off to test the connection.
- If you use your circuit to power a DC motor, keep in mind that the motor's direction of rotation depends on the polarity of its power. If the motor is turning the wrong way, desolder the motor connections and resolder them with the power wires reversed.
- The soldering iron is hot enough to cause minor burns; exercise care in using it. When you're not using it, leave it in its stand while it is plugged in. Always unplug the soldering iron when you are finished working.
- Some types of solder contain lead, a metal known to cause health problems. If the solder you use contains lead, wash your hands after handling the material.
- 22-gauge stranded wire
- Wire strippers
- 15- to 35-watt soldering iron
- Electronics solder
- Long-nose pliers
- Single-pole, single-throw switch
- 9-volt battery clip
- 9-volt battery
- Hand-held digital multimeter
- 9-volt battery-powered motor or light
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