Audible alarm model
Audible alarm model that produces a typical siren sound. When the button is pressed, a sound is heard. When he stops pressing, he changes his tone. Supplied without 4,5 V battery.
The two BC 558/557 and BC 547/548 transistors are mounted to form a simple amplifier. If the amplifier's output signal is redirected to the input, which is done here through the 0,15 mF capacitor, a voltage variation will oscillate the circuit. The characteristic frequency slip of the sirens is caused by an RC circuit by the 10 kOhm resistor and the 100 mF capacitor. The two capacitors parallel to the speaker contribute to the fidelity of your sound by attenuating the high frequencies. The tone is determined by the 27 kOhm resistor, the 0,47 mF capacitor and the 8 Ohm speaker impedance.
|Construction time||3 - 4 h.|
Dos download for free instruction manual.