Very Loud Buzzer Circuit

[Beau Schwabe]

Many years ago (17) I posted on this in the Parallax Forum. What it boils down to is voltage you are sending to the piezo, and if you are driving it in non resonant mode or resonant mode.

See the third post on this thread .... https://forums.parallax.com/discussion/62310/amplifying-piezo-speaker

 

[ckeays]

Most of those parts just make up a switch. The oscillator part only uses a single transistor. Here it is without the unneeded parts:
View attachment 133804
The circuit is similar to the two I posted, above. You can make your own 3-legged inductor by winding a bunch of turns around a 2-legged inductor (you want 10mH or above). Alternately, just use the circuit that doesn't need the 3-legged inductor.

Thanks for your response. I hope to try it in the morning. I am curious to know what the inductor is on my board. Is there any way of measuring to find the Value of the inductor?

 

[ckeays]

Many years ago (17) I posted on this in the Parallax Forum. What it boils down to is voltage you are sending to the piezo, and if you are driving it in non resonant mode or resonant mode.

See the third post on this thread .... https://forums.parallax.com/discussion/62310/amplifying-piezo-speaker

Very interesting! The horn circuit I have operates by a momentary switch to GND. In the circuit you posted, I would somehow have to toggle the pin going to the piezo?
How can I accomplish this without a 555 timer or mcu?

 

[AnalogKid]

I created a schematic of the actual buzzer circuit on the CO board. I triple checked it.

I don't think it is entirely correct. However, it is so similar to the first one in post #11 that they are functionally identical. The tapped inductor is acting as an autotransformer. The original circuit is louder because Q2 can sink a lot more current than 3 B-series CMOS gates in parallel, and the inductor boosts this to a peak signal voltage that is greater than 9 V at the element.

ak

 

[dougy83]

Thanks for your response. I hope to try it in the morning. I am curious to know what the inductor is on my board. Is there any way of measuring to find the Value of the inductor?

There are many ways to measure the inductance, and it depends on what test equipment you have available.

1. If you have access to an inductance meter, use it.
2. If you have access to an oscilloscope, measure the oscillation frequency of the inductor in parallel with a known capacitor, after applying a short pulse from a 1.5V battery. L = sqrt(1/(2*pi*f))/C
3. If you have a signal generator and an oscilloscope (or a multimeter), measure the AC voltage across the inductor in series with a known resistor, when driven by the signal generator.
4. If you have a transformer, use it instead of the signal generator mentioned in option 3 above.

 

[ckeays]

Thanks dougy83. Some valuable info.

I have this meter.

Don't know how accurate it is. It does work though.
Not sure on how to test 3 pin inductors.
It shows inductance on only two pins of the three pin inductor.

I tested the simplified circuit but cannot get it to work.

 

[dougy83]

That meter is accurate enough to do the job.
Just measure the inductance between pairs of 2 pins (not all 3 at once). If you can't get a measurement, either the inductance value is too high or too low for the meter.

The simplified circuit is based on your drawing of the real thing, so it should work, if your drawing and recreation is accurate. You may have the inductor pins in the wrong position.

 

[Nigel Goodwin]

With a 9V supply, the 4049 circuit can drive the piezo with 9V one direction, and 9V in the other; this is 18V peak-to-peak (maximum; limited by 4049 output current). The circuit with an inductor will drive it 9V in one direction, and spikes of perhaps up to 50V (wild guess), in the other direction. You'd expect this to make it louder.

A fair few years ago now the magazine EPE published a PIC based freezer (or fridge) alarm, that used a 12C508 OTP PIC, a small thermistor, and a piezo 'speaker' - I built one, just as a matter of interest more than anything else, and I didn't think it was very loud (for an alarm).

While the 12C508 is only 8 pin, it still had one spare, so I connected the bottom end of the piezo to that instead of ground, and added a few extra bytes of assembler to drive the piezo in bridge mode - which made it a LOT louder (obviously).

I then sent the modifications off to EPE, and they printed it in the following months issues as a suggested update

 

[ckeays]

I ordered some inductors today. I am hoping to build the loudest circuit out of all of these posted.
Thank you to everyone who participated in this thread!

 

[ChrisP58]

I don't suppose that you have an oscilloscope?

If so, look at the voltage waveform on the driven pin of the transducer on the different circuits. That will show you the frequency, voltage, waveshape and duty cycle that produces the loudest sound. Probing other pins of the circuit will also be informative.

 

[ckeays]

I don't suppose that you have an oscilloscope?

Yes I do. I will try it, Thanks,

It would help a great deal if I had a datasheet for the inductor.
Because the part is not marked and is unidentifiable, it is difficult for me.

 

[AnalogKid]

The tapped inductor in the original alarm circuit almost certainly is a custom part.

ak

 

[ckeays]

I got these:

Inductors

I will have them in 2 -3 weeks.

 

[Nigel Goodwin]

I ordered some inductors today. I am hoping to build the loudest circuit out of all of these posted.
Thank you to everyone who participated in this thread!

Bear in mind, piezo's have quite a sharp resonance, you need to be hitting that if you want it loud - this will make it MUCH louder than otherwise.