I accidentally ordered passive Piezo Buzzers instead of Active. I have about 15 of them and they do not work with most simple circuits calling for a piezo buzzer. What can i do with them . I know they require AC signal to work, but I am not far enough along to play with AC yet other than transformers in power supplies.
Are you playing around with microcontrollers? You can connect a passive piezo directly to most microcontroller pins and then toggle the pins at different frequencies to make sound. A trick to make it louder is to toggle both pins to the opposite polarity at the same time to make it louder. For example, pin1=output low, pin2=output high, and then immediately change it to pin1=output high, pin2=output low. Quieter could be leaving pin2 output low and then taking pin1 between output high and output low.
Thank you, Ill try that, hate to waste them.
Do the buzzers have two or three leads?
The three leaded variety are easier, as one transistor is all that's required.
The inductor variant is louder, but more expensive.
Otherwise there's the classic two BJT astable. D1 and D2 aren't needed if the supply voltage is below 6V.
They are 2 lead
All you need is a square wave, equal to the frequency you want the piezo to buzz at.
The previous circuit I posted, with the two BJTs will do that, but it isn't the easiest way. Here's another method using the 74HC14. It's possible to use only one or two Schmitt trigger elements, but they're six in the IC and it's more stable with four: one as the actual oscillator and another three to buffer the signal to drive the piezo. If you need to use a higher voltage, than 6V, then use the same circuit, but with the CD40106, which will work up to 18V.
If you're using a microcontroller, you can just program it to output a squarewave and attach the piezo directly to the output pin. As mentioned above, using two pins, with the opposite polarities and connecting the piezo between them, will make it louder.