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how does this circuit produce four sounds ?

hi everyone

my friend is interested in doing this circuit but he need to understand how it's working

this is the circuit diagram 

 http://www.circuiteasy.com/animation/four%20tone%20siren%20circuit.gif

is it need 3 switches ?
and what the benefit of the transistor here ?


waiting for your help ^^


canucksgirl5 years ago
The key is the chip, where all the magic happens. The sounds are selected by the position of the switches. The transistor is a very basic amplifier.
Re-design5 years ago
It uses 4 different states to get the four sounds. You can do this with 2 Spdt switches. I'd use switches with the center off. The transistor is most probably an amp.