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Recently, I have ordered smt-0440-t-r buzzer from Mouser.

Circuit is as shown in figure.

enter image description here

Microcontroller pin transmits square wave of 4kHz as mentioned in the datasheet. However, the sound isn't audible. When I am at a distance of 1-2cm from the buzzer, I am hearing very low intensity sound. Any fixes?

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  • \$\begingroup\$ Do you have a oscilloscope to check the waveform on the collector of Q4? Also, you could replace R109 with a 0 Ohm link, and remove the capacitor C103. \$\endgroup\$
    – Steve G
    Apr 29, 2016 at 12:00
  • \$\begingroup\$ I have got a square wave at the collector of Q4. Here's what I have done till now: a) I have replaced R109 with 0 ohm and also removed C103, the intensity of sound has slightly improved (2-4 cm range). Not close to audible range though. b) Removed R111 too, even this isn't working. \$\endgroup\$
    – NareshR
    Apr 29, 2016 at 12:30
  • \$\begingroup\$ Do you have D14 the correct way round? \$\endgroup\$
    – Steve G
    Apr 29, 2016 at 12:36
  • \$\begingroup\$ Now, I have removed the diode too. Still not audible. I have checked the current consumption of this circuit, it is 90 mA. I am attaching the datasheet of the buzzzer link . Can it be the buzzer parameters like wrong spl level etc? \$\endgroup\$
    – NareshR
    Apr 29, 2016 at 12:51
  • \$\begingroup\$ 1. You wouldn't normally run a transistor with no current limit into the base. Usually, a transistor switch is run with a beta of 10, so if your collector current is 90mA, your base current needs to be 9mA or so, which would make the base resistor about 240 ohms if your base drive is 3.3 volts. 2. Do you have the + side of the buzzer connected to the supply? 3. Do you have the transistor connected backwards? That is, with the collector and the emitter swapped? 4. How square is your square wave? \$\endgroup\$
    – EM Fields
    Apr 29, 2016 at 13:05

5 Answers 5

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How is your hearing and what is your age? If you are 45 years old then your normal hearing loss at 4kHz is -23dB so you will barely hear it. Hearing aids like mine (I am 73 soon) will fix the loss.enter image description here

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I've had and solved this exact problem that you're having. What Steve said is the key, a piezo buzzer appears electrically as a capacitor.

Now with that in mind, look at your circuit. You're just going to charge the capacitor once, and then it's going to more or less stay charged and produce no more sound.

The loudest way to drive this circuit is using a full H bridge, this will provide a VPP of 2x your input voltage.

Another method that will work is to use a totem pole driver, or an op-amp so that you can drive one side of the piezo high and low. This is simpler, but it will produce half the amplitude.

What I ended up doing in my application is just driving both sides of the piezo directly using 2 microcontroller outputs. This will work fine with an appropriate current limiting resistor, and it may be loud enough for your application.

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  • \$\begingroup\$ can you give a more detailed illustration with a figure? \$\endgroup\$
    – lukeluck
    Oct 12, 2019 at 1:32
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You have checked almost everything and nothing gave a definite improvement. I'm having a guess here that you don't have exactly the same buzzer as in the datasheet. With a specified coil resistance of 17 Ohm this should be a fixed coil / moving diaphragm buzzer, which will work OK with your original circuit.

However if you actually have a piezo buzzer you need a slightly different drive circuit to get a good sound level out of it. A piezo buzzer acts very similar to a capacitor and needs a push-pull driver circuit to charge and then discharge the capacitance of the piezo. However a piezo will work quite well with a small modification to your original circuit, with a 1k Ohm resistor placed across the piezo buzzer to discharge its capacitance.

schematic

simulate this circuit – Schematic created using CircuitLab

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  • \$\begingroup\$ I tried the above circuit, it isn't working though. I have contacted other manufacturer, CUI, waiting for the response. \$\endgroup\$
    – NareshR
    May 10, 2016 at 18:48
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  1. Look at your transducer. If it has a sticker over the sound hole remove it.
  2. The resonant frequency is 4K +/- 500Hz. Try changing the frequency through several other settings to see if resonance is the problem.
  3. Check the drive waveform from the MCU pin. Does it allow the NPN transistor to turn full on and off? Use an oscilloscope to check this.
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  • \$\begingroup\$ I have got a square wave at the collector of Q4. Here's what I have done till now: a) I have replaced R109 with 0 ohm and also removed C103, the intensity of sound has slightly improved (2-4 cm range). Not close to audible range though. b) Removed R111 too, even this isn't working. c) i have also played with frequency from 500 Hz-7 kHz \$\endgroup\$
    – NareshR
    Apr 29, 2016 at 12:33
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I realize it’s been a long time but I found this while looking for info, it was highly placed in the Google search results, so it’s worth adding some useful info that I’m surprised no one ever added.

  1. The first thing to do is to use your multimeter (you ought to have a multimeter, you won’t get very far in electronics without one, and they are very cheap) to measure the resistance of the buzzer. This will give you the DC resistance. If it’s infinite (open circuit) then the buzzer is definitely a piezo type. If it’s fairly small, say 10-100 ohms, then it’s an electromagnetic buzzer. That’ a very easy thing to check and as you can see from the other answers, it’s critical to know which it is in order to know which circuit to use!
  2. This buzzer is probably a piezo buzzer which means the datasheet you linked is wrong! Real manufacturer datasheets for industrial products are VERY reliable (although occasionally they make mistakes) but this datasheet doesn’t appear to be an original manufacturer’s datasheet. It is from Projects Unlimited, which I think is a hobbyist supplier. The standards for hobbyist info are not as high so it’s not surprising this could be mistaken. Specifically, that drive circuit they show in the datasheet is only for an electromagnetic transducer, ie a regular old speaker, and even then it’s not that great of a driver. An electromagnetic speaker really does need a push-pull driver as several people have said.
  3. A tiny piezo element like that is pretty forgiving. The ideal thing would be if you had any kind of audio oscillator that let you fiddle with a knob, rather than needing to write new microcontroller code for each frequency. Connect the piezo element to the output of the signal generator and just turn the knobs to sweep the frequency around. Explore! Often these piezo elements have strong resonances and small changes in frequency can make big changes in loudness. You can also get a very cheap audio signal generator that will be great for this. Take a look on Amazon or eBay or AliExpress or whatever is most convenient for you.
  4. If you’re using an Arduino, for example, and the Arduino runs on 5 volts, and the outputs are rated to source or sink 40 mA, then by ohm’s law you can safely drive a 125 ohm resistor connected to ground. So if you aren’t sure you trust the transistor circuit and you want to do a test with the very most minimal components, you can just put a 150 ohm resistor at the output of the Arduino and then connect that to the buzzer and the other end of the buzzer to ground. This is very unlikely to burn out your Arduino. It’s not an ideal approach at all, but that’s why I’m listing it at the end after all the other things I said.
  5. A cheap signal generator would be convenient, but if you can’t or don’t want to get one, what you want to do then is write a small sketch for the Arduino that lets you sweep the frequency by turning a potentiometer connected to one of the analog input pins. Basically you can make a little signal generator yourself, look around, you will find many example sketches of how to do something like this. Then you can adjust the frequency and see what happens. The important thing is being able to turn a knob to generate a continuous range of frequencies.
  6. For that matter, don’t buy one of the audio signal generators that only has a fixed set of frequencies on a big rotary switch. For example don’t get this https://www.bkprecision.com/products/signal-generators/3001-audio-generator.html because the output is only adjustable in steps. Get something more like this https://www.amazon.com/dp/B07V674HZY/ref=cm_sw_em_r_mt_dp_04HD7CNCFHZPCMEBZ87A?_encoding=UTF8&psc=1
  7. Even when you get everything working right, don’t expect it to be very loud. A tiny buzzer like that is designed to make sounds like the beep that happens when you push the buttons on a simple device, it’s not like speakers on your smartphone. It’s just a little sound. So don’t expect too much.
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