amplifierpiezopiezo-buzzertransducer
I am trying to make a piezoelectric transducer buzz loudly, but have so far only been able to make it create a quiet hum. I have tried using a basic amplification circuit with an NPN, but this made very little difference.
I am working with microcontroller that words at 3.3v. How would I get a loud buzz even for a short period of time, from a piezoelectric transducer similar to the below image.
I don't think trying to get white noise out of a piezo is a good idea. Piezo transducers usually have far from flat frequency response, often with a major and a few minor resonance peaks. They can also be non-linear, meaning they can produce frequencies that they weren't driven with. Then what about the pickup? How do you know how flat that is?
I see two possibilities:
Try to put a reasonable sine wave into the piezo and sweep it over the frequency range of interest. Of course you know the frequency at any point in time, so you filter the received signal for that frequency only. This eliminates harmonics and most other distortion the piezo can add.
Always drive the piezo with exactly the same short pulse waveform. Ideally this would be a impulse, but you'll have to compromise a bit on the infinite amplitude and infinitely short time. This can be as simple as a digital pulse of the highest amplitude the piezo can take, lasting maybe 20 µs or so. It doesn't have to be accuartely anything in particular, only highly repeatable. A full size 20 µs pulse is something the electronics can do easily and very repeatably.
One good thing about piezos is that they generally are fast. You should be able to produce a impulse that is good enough for detecting what happens to the audio range frequencies.
This is the method I'd probably try first.
In any case, you have to calibrate the system. Assume you don't know much about the piezo and can't rely on the pickup either. Calibrate it in open air with nothing around it, with the two transducers separated about as far as the input and output of the insturment you want to measure. For example, mount them about 2 feet apart if you want to test a clarinet.
Any one impulse will have a lot of noise on it. The advantage of this system is that you can repeat impulses at a decent rate and accrue signal to noise ratio by getting lots of samples. Ambient noise will also eventually cancel the same way, since presumably it is not synchronous to your impulses.
During calibration, you essentially measure the impulse response of free air and declare that to be a flat spectrum. It will actually be quite a mess, but as long as there is enough signal to noise ratio accross the full spectrum, you use that as a baseline to compare real measurements with later. When making real measurements, you divide the spectrum you get from the received impulses by the spectrum saved from calibration. That should yield the actual transfer function of the instrument.
Why don't you just use the circuit design recommended by the buzzer manufacturer in their data sheet. I.E. this circuit:
This uses a simple CD4049 chip, two resistors and a small capacitor. This curcuit gives you the gain you need to make the oscillation work.
Best Answer
Such transducers work best with higher voltages, like 9V or more. A straightforward solution would be to generate that voltage using e.g. a charge pump, then use the NPN transistor to amplify the MCU signal to that voltage. Depending on the project, you may already have that voltage available.
Another common option is to drive a small step-up transformer with the secondary winding connected to the buzzer. I have seen piezo transducers in fire alarms which are driven by 1:10 transformers, and those are indeed pretty loud.
A push-pull configuration (which should have the same effect as doubling the voltage) can be implemented with a single NPN transistor as well:
simulate this circuit – Schematic created using CircuitLab