not gate oscillator

[audioguru]

The lowpass filter is only a single capacitor, C6. For it to pass a human whistle then it does not reduce the level from the beeping oscillator enough.
I think it will keep on beeping.

 

[vlad777]

If you have the circuit physicly and it's a piezo please do a little swap
with a small coil speaker and let us know.
The inpedance of the speaker should be high i think.

 

[audioguru]

If you have the circuit physicly and it's a piezo please do a little swap
with a small coil speaker and let us know.
The inpedance of the speaker should be high i think.

The circuit is designed to drive a 10k ohm piezo transducer with a signal of only a couple of mA. Nobody makes a 10k ohm speaker, 64 ohms is the highest I have seen and this circuit will not drive it. Adding a transformer to a speaker will simply reduce its output level.

The project needs a real microphone, a good preamp circuit and a sharp bandpass filter for whistle frequencies.
Maybe the mic preamp can be muted when the output of the project drives a piezo beeper.

 

[BrownOut]

Maybe I am wrong but I calculate 4.8 kHz frquencey for the last stage.

I take back what I said about the HPF preventing feedback from the oscillator. Indeed, the circuit oscillates as long as C7 is charging, the the oscillation is halted, and the circuit awaits another stimuli.