arduinopiezopiezo-buzzer
I recently borrowed an Arduino Inland Basic Starter Kit. It includes an active and passive buzzer. What is the difference? I can hear a difference in sound when I use the tone() command. Anything else?
How can I identify which one is which? Are there any specific commands for each one?
The problem with the relays isn't that of current, but of voltage. You will need to supply 12V to the coil of those relays in order to get it to energize.
One option is to find relays that only require either 5V or 9V instead, so that it can be either powered from the Arduino's supply or from a 9V battery. You will still need the transistor if using 5V relays, since at that point the coil will need more current than the Arduino output driver can provide.
Another option is to draw power from the incoming AC line and put it through a regulator to get the 12V required to operate the relay. Additionally, a 5V regulator will get you the power you need for the Arduino so that the entire apparatus is powered off the line.
You need to run it at 2.40 kHz get maximum sound pressure level (SPL). The transducer is mounted in a ported acoustic cavity which has a definite resonant frequency. Here is a typical response curve for a 2kHz transducer:
You'll still get a fair bit of noise at other frequencies (you can even use these things as horrible little speakers), but not maximum.
But most importantly, and as @RichardCrowley says ,that 100uF is totally wrong, get rid of it. And take care you don't accidentally leave it with the output on at 100% duty cycle, it will probably fry the coil.
Best Answer
An active buzzer will generate a tone using an internal oscillator, so all that is needed is a DC voltage. A passive buzzer requires an AC signal to make a sound. It is like an electromagnetic speaker, where a changing input signal produces the sound, rather than producing a tone automatically.
To identify them, if you apply a DC voltage to them and it buzzes, it's an active.
As far as commands go if you want to control the pitch, you would need a passive buzzer. PWM on the Arduino can be used to control the pitch and the volume at the same time (which may or may not be what you want). If you wanted to change just volume or just pitch I suppose some external circuitry would be required to change the amplitude without changing the voltage, and vice versa.
A couple sources: Source, Source, and Source, as well as @Peter Bennett's comment.