Alarm Sound

Alarm

I describe the experiment that will be a noise like a small siren. It will be used as an alarm. For this project,

I will be using a programmable unijunction transistor or PUT.

The PUT blocks current until its internal resistance drops to allow flow from the “anode” to the “cathode.”

It is depended choosing a voltage to the gate. At first I will make the Slow-Speed Oscillation circuit.

It will show how works the PUT with LED. At second I will add a speaker with the npn transistor.

What we will need:

• AC adapter(You can use arduino for power.), breadboard, wire, and meter.

• LED. Quantity: 1.

• Resistors, various.

• Capacitors, various.

• Transistor, 2N2222 or similar.

• 2N6027 programmable unijunction transistor (PUT). Quantity: 2.

• Miniature 8Ω loudspeaker. You can take it from an old radio.

At first we need to make first scheme. The 15K resistor and 27K resistor establish the voltage at the gate. The 470K

Resistor supplies the anode of the PUT, but the PUT begins in its “off” condition,

Blocking the voltage. So the voltage starts to charge the 2.2 μF capacitor.

You can add the capacity to scheme. If you substitute a much smaller capacitor, it will charge much more quickly,

And the LED will flash faster. Suppose you use a capacitor of 0.0047 μF(fourty seven nanofarads) (which

Can also be expressed as 47 nanofarads, or 47 NF). The human ear can hear high frequency, that will make by the speaker.

For loudspeaker make more noise, you can add a transistor. Yon can set it like a scheme.

In addition, you can modify the scheme like a picture. That's all.