Many alarm circuits use a piezoelectric bender for a loud noise.
Piezoelectric transducers, also called buzzers or benders, make inexpensive and handy electronic noisemakers. Thinner, lighter and simpler in design than a speaker, the transducer contains a flat crystal bonded to a thin metal disk. When driven by a signal at the disk's resonant frequency, it makes a loud beeping noise. To drive the bender, you need a simple circuit that generates an audio-frequency signal. You can get this circuit together and working in about an hour.
Instructions
1. Touch your hand to an electrical ground, such as a cold water pipe or metal conduit. This will remove static electricity from your body.
2. Seat the CD4011 integrated circuit on the breadboard so that its pins straddle the channel in the board. Press the IC in firmly, making sure that the pins go in straight.
3. Cut two pieces of wire about 2 inches long, three pieces of wire about 3 inches long, and 2 pieces 12 inches long. Trim about ¼-inch of insulation from both ends of each wire. Solder one 3-inch wire to each of the SPDT switch's three terminals. Insert the free end of the wire soldered to the switch's center terminal so it connects to the IC's pin 2. Connect the wire soldered to the switch's "normally open" contact terminal to pin 14. Connect the remaining switch wire to pin 7.
4. Insert one lead of the 1-megohm resistor so it connects to pin 1. Place its other lead into an unused column on the breadboard. Insert one lead of the 560K-ohm resistor into this column. Connect its other lead to pin 5. Connect pin 5 to 6 with a 2-inch jumper wire. In a similar manner, connect pin 6 to 3.
5. Insert the capacitor so one lead connects to pin 4 and the other lead connects to the column shared by the two resistors. Connect one lead of the 18K resistor to the IC's pin 4. Insert the other lead into a unused column. Place the base lead of the 2N2222 transistor into this column. Connect its emitter lead to pin 7. Connect its collector lead to an unused column. Insert one lead of both the piezo transducer and the 1K-ohm resistor into this column. Connect the other lead of both to pin 14.
6. Insert one end of a 12-inch wire so it connects to the IC's pin 14. Connect its other end to the positive terminal of the DC power supply. Insert one end of the remaining 12-inch wire to pin 7. Connect its other end to the power supply's negative terminal.
7. Switch the power supply on. Press the pushbutton switch. The piezoelectric disk should make a loud beeping sound.
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