Siren sounds with 555 timer and 5v Buzzer
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I'm looking to have my Homini Complete Room Module be able to sound an alarm when it detects either smoke or carbon monoxide through means of just a 5V buzzer. My initial thoughts were to have a PWM pin pulse the buzzer in various speeds to create this sound, but then I started to think of the workload it would require to have this be done in software while allowing readings from the various other sensors on board to still be read. While doable i thought that if i could create this in hardware it would allow it to be less software dependent.
Due to these requirements of mine, I was thinking about having 2 555 timers generate the pulsing sound on the buzzer. Am I correct in thinking that the trigger pin of a 555 timer is a active low pin meaning that to start the 555 timer we just drop the trigger pin to <1/3 of the supply voltage, which in this case is 5v. So if i take the pin to 5v (HIGH) it would turn the 555 timer off, then soon as i drop the pin to 0v (LOW) it would then turn the 555 timer on and produce a sound?
The question i'm asking here is, To enable/disable the siren, could i just make pin 2 on both 555 timers 0v to make the siren start to sound? Or would it be a much 'better' solution to use a npn transistor as a switch on the 5v line of the 555 timer circuits and have their trigger pins (pin 2) permanently connected to GND?
What is the best route to take here?