Miniature, pleasent-sounding buzzer

Question

I have an Itaki cooking lunch box, which is a tiny Japanese 200W steamer, made to take your lunch to work and heat it.

Its operation is pretty simple: It has a heating element, switch, pilot light, and temperature-controlled switch. You put water it in, and when the water boils off, the temperature rises and turns the heating element off.

The trouble is that there is no audible alert when it is done - you have to set a timer and keep checking the pilot light.

I want to add a buzzer that will make sound when it's done cooking. My plan is to take the voltage that will be across the temperature-controlled switch. I'll have a capacitor in series to drop the voltage, and a full-wave rectifier to make DC to power a 5v or 12v buzzer.

My issue is that I'd like to use a buzzer that sounds pleasant, not annoying. A repeating "ding" would be nice, but I can't find anything to buy that sounds pleasant and will fit in the small space I have.

Do you know where I could buy such a sounder?

shabaz · Answer

Hi Steven, There's quite a few ways, but I don't know of any single off-the-shelf sounder that is pleasing. Mostly they are designed to be unpleasant and to alarm : ) I did a doorbell project a while back, and I concluded that if I wanted a nice chime, then I'd need to do it digitally, so that's what I did, it involves a lot of effort though. If you search aliexpress, you'll find tiny (stamp sized) boards that are intended as chime effects for doorbells. They require a miniature speaker (not piezo disc). It's a low-cost electronically generated chime so it sounds electronic : ) You can even get sound recording boards for custom sounds, but they won't be hi-fi. Below is a circuit for a nice-sounding piezo output generator, it makes just a constant tone, not a ding, but it's a kind of old-fashioned design (i.e. the type that sometimes sounds as if it is drifting slightly as the battery dies : ). I found it pleasing because I like that sort of analog drift, but it is subjective. It requires a small tranformer to be wound though - use very thin enamelled wire (0.15mm approx maybe), the left side has about 100 turns, and the right side has 18 turns (you can wind the right side one on top of the other one. You can replace R1 with two 22k resistors if you like (it's not critical) and the circuit runs from 1.5V to 9V. Alternatively, for an easier analog sound, consider using a 555 chip. If you arrange two 555s in the right way (it is experimental, you'll have to try different values until you finds something pleasing), you can make it do siren-type sounds i.e. slow-changing, or alternatively faster vibrato style effects. See here to learn how to use the 555, with some examples: 50 - 555 Circuits Depending on how far you want to go, you could even consider MP3 boards. That would be high-quality, but possibly excessive (depends how far you wish to go to reach the sound that meets your needs : )

jw0752 · Answer

Hi Steven, Your idea interested me so I breadboarded it on my bench. I used your description of a power circuit as shown in this schematic: I found a small sonalert that sounds a lot like the steam whistle of an old fashion teapot. At 5 volts it drew 20 mA so using the Xc formula I calculated that I would need about 500 nF in series with the bridge rectifier in order to supply a comparable current from my 115 V 60 Hz line voltage. In the schematic above, the label on the capacitor should read 100 nF / 4 mA. You will have to measure the current draw at operational voltage for the sonalert that you choose. It might be best to choose one that has a steady sound as this circuit is designed assuming a pretty constant load and the circuit will attempt to deliver a current of 20 mA by increasing the voltage across the buzzer. If you do decide to use a sonalert that doesn't present a constant load to the line you could put a zener diode across the buzzer to keep the voltage from damaging it. The challenge will be to get all the components into a safe enclosure since you are dealing with line voltages and fatal shock hazards. Here is the result of my test circuit.

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I look forward to seeing your completed build. John

jw0752 · Answer

Hi Steven, You could perhaps salvage a sound module from a greeting card or a cheap toy to get the size and sound that you want. John

clem57 · Answer

And to play it you can use this example from one of our members Audio project: Agony Box . Check out the video... By the way, tonight I found one in Micro center for $25 which is a steal...

Here is a picture to give you the size, approximately. It can also light up. BTW, it can be programmed to respond to external voltages less than 3.3 V or Temperature sensor (thermistor)

BigG · Answer

Yes, I too find many off-the-shelf piezo buzzers to be too high pitched. I remember trying out this one years ago which had a lower pitch (resonates @ 2900Hz) and was also loud enough (90dB). https://ie.farnell.com/moflash-signalling/ae20m-12fa/buzzer-piezo-12v-ac-dc/dp/1649236 EDIT... actually, it well may have been this one (resonant frequency 450 Hz): AE30M-FT-01 AE30M-FT-01 https://ie.farnell.com/moflash-signalling/ae30m-ft-01/audio-signal-indicator-90db-14v/dp/2420433

clem57 · Answer

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Here is a ding you can use. Just repeat as you wish

Miniature, pleasent-sounding buzzer

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