simplest way to create an activatable alarm on a speaker?

Question

I have made a circuit that produces a 3.3V high when its active and 0V when it is off.

Now I would like to extend it with a speaker that plays some sort of alarm (although it shouldn't be too intrusive, but clearly understandable) that I wan't to activate with said circuit. So it plays some sort of tune or alarm for as long as the signal is high.

So what would be a simple way to create a triggerable alarm/tune without the need for a computer?

Ideal would be some sort of chip with preprogrammed music or something on it that I could just hook up to a speaker and that could simply connect to the output of the circuit.

I have looked for something like that but it doesn't seam to exist, they always require a computer or a raspberry pi to set the samples.

And just connecting a speaker to the signal outright just creates an irritating tone.

Answer 1

Sonalerts (trade name) are piezoelectric sounders that can make a wide variety of noises when power is applied, with no other components. You may hear one version as the audible signals on some pedestrian crosswalks. They should be available from most major distributors.

Answer 2

A relatively simple circuit that might get the job done is an oscillator based on a NOT gate (also happens to be my choice for Stack Exchange icon).

This will create a single frequency square wave tone where the frequency can be adjusted by the capacitance value C. The value of C will need to be relatively high to bring frequency down to audio range. Without any amplifier, you are relying only on the output current of the transistor(s) within the NOT gate to drive the speaker which may or may not be sufficient for your application.

Answer 3

In the last century I could buy a chip which produced a (rather distorted) 3-tone descending major chord chime with decay. Used for door chimes. As I still hear the sound in the bake-off section in Lidl, I guess it or similar chips are available.

Answer 4

just connecting a speaker to the signal outright just creates an irritating tone

Actually, it should only create a click, unless you have poorly filtered 3.3V power.

A mechanical device that operates at 3.3V with sonic output could be a doorbell-style mechanism. The basic principle of these is a delayed turn-off switch, where, after the clapper swings to hit the bell, an electrical contact opens which turns off the power to the electromagnet that swung the clapper over...

Another option might be a low-voltage DC motor, either with an eccentric weight (like some old phone/pager vibrators) or a moving part that (a) rotates a music-box drum mechanism, (b) drops a marble from a feed hopper every time it rotates or (c) draws a bow across a violin or (d, e, f...)

Few options are as energy efficient, though, as the resonant-plate beeper in an alarm watch. That requires modulation, not just voltage, applied, but you can tune it for sound frequencies that are very easy to hear.