How to Make a Burglar Alarm
Presented by Engineer and Inventor Nick Donofrio
Senior Vice President, IBM
During a visit to Sleepy Hollow Middle School in Westchester County, New York, Nick showed seventh- and eighth-graders how to make their own burglar alarms. You can try it too!
9 volt battery, wire, cardboard, aluminum foil, cellophane tape, and a small electric buzzer
- Cut a piece of cardboard about one and a half inches by four inches and fold lightly in half.
- Tape strips of foil around the cardboard.
- Tape a clip wire to each of the pieces of foil.
- Join the wires in a circuit with the battery and the buzzer.
- Set up the burglar alarm near a door so that anyone coming through the door will step on the cardboard and set off the buzzer.
How it works:
When the two pieces of foil are pressed together, the circuit is completed and the electricity can flow. The flow of electricity through the electric buzzer causes it to make noise.
Some ideas to try:
Replace the buzzer with a light emitting diode. Connect the positive (+) side of the diode to the cardboard switch, orÍ Connect a resistor in the circuit between the battery and the buzzer to change the sound.
Electrical engineers keep track of three quantities when they design circuits:
Voltage is electrical pressure or force. Symbolized by "V", it is measure in volts. Current is the flow of electrons passing a given point. Symbolized by the letter "l," it is measured in amperes. Power is the work performed by a current. Symbolized by the letter "P," it is measured in watts.
We generate voltage by using batteries, generators and solar cells. We get current by placing voltages across things such as buzzers, lights, resistors and other interesting devices. Using voltage to make things happen is the purpose of electronics.
Ohms Law is the relationship between voltage, current, resistance and power.
V= l x R and P = l x V.