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.
Beeps don’t usually come from a speaker, no. You might find this old ELI5 about electronic sound interesting.
Linking to Reddit on Lemmy is blasphemy. (But thanks for the link lol its informative)
Usually it’s not exactly a speaker, but it does involve a controlled moving diaphragm. In a piezoelectric buzzer, a current applied to the diaphragm causes it to oscillate, and the size and shape of the diaphragm determines the tone AFAIK.
It may be theoretically possible to engineer such a device into a rudimentary speaker. I mean, people have done it with Tesla coils and player pianos, so hey, anything is possible?
Interesting. I’ve never heard of a piezoelectric buzzer before. This is the answer I was looking for. Thanks!
You can also make hard drive heads play music. Poor quality music, but music.
Multiple piezoelectric buzzers could probably play a tune if you tune them to individual notes. Not sure how to tune them, but probably cutting them, or putting bluetak on them would alter their note.
You can also make hard drive heads play music.
How does this work?
A basic speaker is functionally a copper coil next to a permanent magnet. A hard drive head (although I guess more specifically read arm?) is also a copper coil next to a permanent magnet. So if you push an audio signal through the coil, it vibrates and makes sound. It’s missing the diaphram/cone part of the speaker, so it’ll be very tinny.
If you want to make one yourself, get a broken hard drive, and an old pair of headphones, and connect the wires to the coil and play some music.
https://www.instructables.com/Hard-Drive-Speaker-More-Instructive-Version/
Don’t forget floppy drives
Never tried floopy drives, good acoustics?
Have you not seen Flopatron?
Apologies for the YouTube link but I don’t think he posts things anywhere else.
Never seen it before, never been so happy getting rickrolled :D
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.Interesting thank you. The integrated drivers thing would make it difficult to hack but I guess its always possible to crack the smoke alarm and replace the drivers, if someone really wanted to get their hands dirty
I would guess that the units used in smoke alarms and microwaves generally have integrated drivers that only operate at a single frequency.
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.
The only ones I’ve ever used myself area is the DC variety. Apply power: beeeeep; stop applying power: <sound stops>
I don’t know which ones are more commonly used in consumer electronics.
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.
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.
I don’t have any answers - but now I wonder if your idea would be easier when working with one of the fancier smoke detectors with voice alerts. Those have pre-recorded voice alerts that “speak” when an alert occurs, rather than beeping. Those pre-recorded messages must be stored somewhere in the smoke detector.
Putting in a request now for the intro noises from Korn’s “Twist.”
