Very Loud Buzzer Circuit

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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?
 
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?
 
ckeays said:
I created a schematic of the actual buzzer circuit on the CO board. I triple checked it.
Click to expand...
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
 
ckeays said:
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?
Click to expand...
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.
 
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.
 
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.
 

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

ak
 
ckeays said:
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!
Click to expand...
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.
 
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