jow voltage battery beeper

hello guys
please do help me to develop theory on the circuit below i need to explain for a semnar

the circuit lies in the below url

please telll me wat theory is needed to explain the ic's 555 timer n the transistor working there
how is the duty cycle changed


Battery Low Voltage Beeper

my maill id iskishoretvk9@gmail.com

**broken link removed**

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k

i got most of tat but can i know the operation of the diode there in the circuit
please n thanx for ur sujestion

You want us to do your homework for you?

This looks like an over complicated way of doing it.

This simplest is to use an LM311 and a pulsed piezo buzzer.

If you must build your own oscillator, then I'd opt for a quad LM339, configure one as a low frequency oscillator, the second as an audio frequency oscillator and the third as a comparator.

I don't see any reason why this should require more than one IC plus a voltage reference.