Another circuit born from necessity, the story goes like this, the door bell I have is a wireless thing that needs it's battery changing every 2 minutes - it constantly draws 600uA in standby and jumps up to 80mA when the bell is pressed and then there is the transmitter which I haven't bothered measuring.
so because during this week the batteries went flat I missed the post twice, I assumed that the first time it was just because I was playing music too loud and didn't hear the bell but the second day this was not the case so I figured time to make my own with the following specs - less standby power use and loud as fuck.
anyway what happens in the circuit is that pressing the switch discharges the capacitor into the IC which allows it to carry on beeping untill the capacitor drops below a certain voltage I won't go into detail about the fucntionality of a Logic NAND gate because there is a brilliant site that covers it in a simple manner HERE
however I have taken a screen capture of my scope to show you the voltage waveform as it discharges into the circuit. you'll notice at first the waveform has bumpy bits, that's the actual beeper circuit powering the speaker and as you can see the beeping lasts for about 1.5 seconds which is long enough when you hear this thing.
it draws about 150uA in standby and about 30mA when it's making a sound so it beats the stupid piece of crap I currently have.
sorry for the lack of real explanation on this circuit but I've got a bastard of a migraine