TRIANGLE WAVE ASTABLE:
Adjust the warble rate using VR1. Start with PR1 set at minimum, fully anti-clockwise.
Set Range 2 - (31Hz-850Hz) and use potentiometer to change frequency.
Or Range 3 - (700Hz-18KHz, can also produce some very piercing sounds)
Set Range 3 - 2 seconds or more sounding the siren, use potentiometer to change duration.
The PIR sensor output goes low when a presence is detected.
The PIR connects to the trigger input of the monostable. When triggered low, the monostabl starts its timing by sending its output high.
The output from the monostable connects to the Reset input on the AStable. When the input is high, the astable starts to oscillate.
The Triangle Wave astable connects to the FM (Frequency Modulation) input of the Astable which causes the output frequency to vary in proportion with the voltage. The more voltage, the more deviation from the original frequency creating a rapidly rising and falling tone.
The output from the Astable is connected to the Darlington Driver which boosts current for the speaker.
By turning VR1 on the Triangle Wave Astable gradully clockwise, the speed of the warbling will increase to a point where it matches the frequency of the second astable. This can produce some very unusual sounds. For a standard siren, turn VR1 fully anti-clockwise