Quote Originally Posted by Telemachus View Post
I have taken apart a kitchen timer, and it has a similar circuit to the piezo buzzer mentioned earlier in this thread. There is a large inductor coil attached where the buzzer is.

In this picture:

http://www.picbasic.co.uk/forum/atta...9&d=1264966885

Can someone tell me what is the purpose of Q1? Looks to be a surface mount NPN transistor.

One of the leads to the piezo is always high, and the other one seems to be attached to the collector (not emitter!) of this transistor with the emitter going toward the IC through R1, although I could have my pinouts wrong.

How does the IC control the PWM going to the piezo by means of the transistor?

Thanks!
You've got the pinout wrong... the 22K resistor is on the base, the emitter looks to be tied to ground (check it with a meter). It sounds like the piezo is in the collector making it an open collector. You can tie the coil in parallel with the piezo to get the same flyback effect that Mark_s was talking about. Again, it's resonant so you have to play with the frequency to get it to "go"...