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I have a Piezo buzzer that has an internal transducer so is able to take 24VDC and work. This one has a continuous sound. Just a beeeeeeeeeeeeeeeeeeeeeeeee...

I have a 24V output that needs to power an alarm sound (has to be piezo). The alarm has to be On/Off, a beep beep beep. Not particularly concerned about the exact frequency, or sound, or even how long the beep and pause is for. Just has to be a beep, and preferably customizable if required.

I thought of using an ATTiny but then I need a switching regulator to provide 5V to the microcontroller, and then another power transistor to run the buzzer. That makes 3 fairly large components (footprint is important) and the price goes over £10. I thought of 555 but definitely, the footprint is too large because even the 555 won't take 24V.

I cannot for the life of me figure out how to make the buzzer switch on and off, like a slow flip-flop, or PWM maybe, without using a microcontroller.

By the way, THIS and THIS is exactly what I am talking about. I will definitely use these for my application, but I need to figure out how to make a continuous one pulse. Or even better, how to take just a regular Piezo element (without internal transducer) and get any frequency I want out of it, with as few components as possible. I can do it with an ATTiny as mentioned above, but running it 24V introduces two additional components.

I highly appreciate any help I can get.

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closed as unclear what you're asking by Chris Stratton, Sparky256, RoyC, JYelton, Bimpelrekkie Aug 8 at 14:06

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    \$\begingroup\$ You keep telling us that the footprint is important but you never tell us how big it can be. What do you mean by a "continuous one pulse"? What do you really mean by "any frequency I want"? \$\endgroup\$ – Elliot Alderson Jul 13 '18 at 11:10
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Use an LM122 configured as an oscillator. Tie the output as

schematic

simulate this circuit – Schematic created using CircuitLab

If you had a 12 volt supply, you could use a 555, but that won't work at 24 volts.

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  • \$\begingroup\$ Looks good but I cannot find the LM122 to purchase, unfortunately. I think i'll try the astable multivibrator. \$\endgroup\$ – M.. Jul 16 '18 at 12:25
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You could make the classic two-transistor multivibrator and set it to oscillate at the beeper on/off rate. Use a third transistor to then switch the power to the beeper.

Don't forget to put a reverse diode across the beeper. Piezo elements can have kickback similar to what inductors do.

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  • \$\begingroup\$ I think this is it. I initially thought about an astable multivibrator but for some reason dropped that idea because I thought it would be less efficient. I will test this and let you know if it worked or not. Thank you for your help. \$\endgroup\$ – M.. Jul 16 '18 at 12:41

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