Buzzer Problem

I had an electrical engineer help me with the schematic/design for a PCB I recently ordered. The board arrived yesterday and for some reason the piezo buzzer is extremely quiet…I can hear it (sending tones to it via Arduino’s tone() library) but I have to hold my ear right up to the board.

I’ve attached an image of the part of the diagram related to the buzzer, and here’s a link to the model of buzzer we used:

https://www.digikey.sg/product-detail/en/cui-devices/CPT-9019S-SMT-TR/102-3761-1-ND/6012450

The buzzer is connected to D8 on an ATMega328. Anyone have any ideas what could be making the sound come out so quietly? The engineer added a transistor to the board I can see, and when I laid this out on a breadboard beforehand I did not use a transistor. Could that be related?

Thanks!

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The data sheet says:

Buzzers Transducer, Externally Driven Piezo 3V 5mA 4kHz 65dB @ 3V

Are you driving it at 4kHz?

How to post an image
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After over 100 posts you should know this...

Remove the transistor and drive the buzzer directly from D8.

If that's what they teach electronics engineers I am glad I don't have a degree in electronics.

What is the part number for Q7 ?

Show us a good image of the board.

A piezo buzzer must have a (1K) bleed resistor across to work with a (class-A) single transistor.
A piezo is basically a capacitor, and will be charged to the supply voltage after the first pulse.
Then it won't produce sound any more.
A 3.3volt supply is also low for a piezo. it will be very quiet.

Use the toneAC library, and connect the piezo between TWO Arduino pins.
Driving the piezo in H-bridge mode will give you the loudest sound.
Might be wise to add a 220ohm resistor in series with the piezo, to keep peak pin current under the max limit.
The piezo will have a resonance frequency at which you have the loudest sound.
Leo..

PerryBebbington:
Remove the transistor and drive the buzzer directly from D8.

If that's what they teach electronics engineers I am glad I don't have a degree in electronics.

This was the correct answer. I bypassed the transistor and the buzzer works great without it. Thanks!!

elveax:
This was the correct answer. I bypassed the transistor and the buzzer works great without it. Thanks!!

You've welcome.

Do you know why?

I don't know why and I am curious if you care to share?

A piezo electric transducer behaves pretty much as a capacitor. Capacitors pass AC and block DC. Putting one in series with a transistor collector means there is no DC path to the transistor so it can't generate any signal for the transducer. The digital output has 2 drive transistors, one to each supply rail, so can charge and discharge the capacitance of the transducer.

Follow the link, "Buzzer Basics" in the link you provided. The resistor is explained there, too.

toneAC (post#5).