This simple circuit is perfect for an alarm. The beeper dont beep all the time but in alternance. You don't need special skills in electronics but is is recomended to know some basic electronic components to understant how it works.
The diagram is at the end of this instructable.
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Step 1: Place Transistor
Place two transistors in your bread board like in the image. One of the transistors is placed on the opposit way.
Step 2: Place Resistors
Place two 1 kiloohm resistors next to the middle pin of each transistor and the other end of the resistors in the outer bread board line (+).
Place two 330 ohm resistors between the 1 kiloohm resistors, and connect them to the collector pins of each transistor and to the first line of the bread board (+).
Step 3: Add Capacitors
Add two capacitors. Each of the caoacitor has one pin connected to the center pin of the transistor (base) and the other pin is connected to the collector of the other transistor. You must also add cables from the outer transistor pin (emitter) to the blue bread board line (-).
Step 4: Build Second Oscillator
Start to build the other oscillator in the same way. Place two transistors, 2 1kilohm and 2 330 ohm resistors next to them.
Step 5: Add Electrolitic Capacitors
Like the first oscillator you need to add capacitors but you need to use bigger capacitance to acheave a lower frequency. Connect the two capacitors like the other two, one pin (negative side) in the middle of the transistor (base) and the other pin to the other transistor (collector). Do this for each of the capacitors. Also connect the last transistor pin (emitter) to the second bread board line (-).
Step 6: Add Beeper and Connect to the Battery
Add the beeper liks showen in the image. Move the white cable on the image from the second bread board line to one of the collector of the thansistors of the second oscillator. The circuit is done, if you connect the power supply it will beep.
Step 7: Part List
For this beeper you need :
- 4x NPN transistors (bc547)
- 4x 1 kiloohm resistors
- 4x 330 ohm resistors
- 2x 10nF capacitors
- 2x 47uF capacitors
- 1x piezo or speaker
- 1x power source (9v)
- Breadboard with jumprers
You can use components with different values it will change the sound and frequencies but it schuld still work.