I’m asking not specifically about smoke detectors but any device that beeps but does not make any other, non-beeping sounds. Examples include microwaves, the timers on ovens, the fare system on a bus when you give it your fare, the little beepy heart monitor things in hospitals and old-school digital watches. These things beep but they seem to only beep; they do not make any other, non-beeping sounds.
So my question is: how do these things beep? It must be a speaker right (?), and if it is a speaker then why do these devices never make any other sounds other than beeping? (Because presumably speakers have a greater range than just a few beeps.) Or do these devices have specialized speakers that can only make a few sounds? If so, how do these speakers work?
I’m not sure if I articulated this very well but hopefully that makes sense.
https://www.labdarna.com/en/understanding-piezo-buzzers-how-they-work-and-how-to-use-them-in-electronics-projects
They use piezo buzzers which work differently to most speakers. I would guess that the units used in smoke alarms and microwaves generally have integrated drivers that only operate at a single frequency. However, it is possible to drive piezo discs at different frequencies. Their ouput will always approximate a
soundsquare wave though, so don’t expect to be able to use them like a normal electrodynamic/ voice coil speaker to play arbitrary sounds.Depending on how briefly they can be triggered i wonder if it could be fired in a controlled enough temporal pattern to create recognizable notes. Human hearing goes down to 40 cycles per second, so if it can fire in burst of less than a 40th of a second then that could work
The link I included in my comment goes over driving one in recognizeable notes to play the nokia tune. It’s worth a read if this concept interests you.
Yeah, you could more easily create a rhythm than a full melody. If you get a few devices, which beep at different frequencies each, you could do a lot more by having them beep in succession and in intervals.
Of course, this requires that they’re roughly in tune, which may not be the case at all. 🥴
Piezo buzzers have a resonant frequency they’re strongest at. Two-pin piezo disks need driving at the desired frequency. Usually only a GPIO pin (PWM-capable if possible) and a resistor is needed. Three-pin disks provide a phase-shifted feedback to the driving transistor to keep oscillating at the resonant frequency. Some include that whole circuit inside their housing so they have just 2 pins but those are for DC power, only the volume can be somewhat adjusted by changing the input voltage.
You can if the buzzer signal is only used to trigger a secondary circuit that does what op is looking for.
That’s what I would do. Hook jumpers from the buzzer to the play button of an mp3 player. That way if the music system fails, the buzzer still wakes you up.