How to connect Buzzer to PIC?

[mtripoli]

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"...

[Telemachus]

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"...

Thanks, after some more research, I realized the true pinout.

Actually, what I am trying to do is to remove the coil and piezo entirely, and have the transistor act as a switch to turn on and off a higher voltage (3.3volts) that will be fed to the input pin of a PIC. Therefore, when the kitchen timer goes off, the PIC will read the PWM output as a digital signal to run a routine prior to resetting the kitchen timer to start counting again.

What I have come up with so far is to disconect the coil from the transistor's collector, mount instead a 3k3 resistor between the collector to PIC VDD (3.3V) and connect the PIC input pin on transistor's colector. With the emitter of the transistor connected to GND (I will ground the PIC to the CMOS circuit). That way, when the timer goes off, it should trigger a "buzzer" that in non audible, but compatible with the VDD voltage that my PIC can read digitally.

This is a timer circuit to snap the shutter on a Cannon SLR camera, and I have found that using the kitchen timer is cheaper than it would be to buy the LCD and buttons needed build the circuit completely based on a PIC.

[mtripoli]

A digital Canon SLR? If I recall, there is a group of pads inside the the battery door. Bridging these pads results in focus adjust and shutter release. I used a 1K resistor (or something) to play around with this. I was going to make an RF remote control for my camera but got side-tracked with something else (about 5 years ago). There's a bunch of info on the net about this stuff. I think you can use just a relay to do this...

I'm missing the point of using the kitchen timer. You can do everything you want with just the PIC...

[Telemachus]

A digital Canon SLR? If I recall, there is a group of pads inside the the battery door. Bridging these pads results in focus adjust and shutter release. I used a 1K resistor (or something) to play around with this. I was going to make an RF remote control for my camera but got side-tracked with something else (about 5 years ago). There's a bunch of info on the net about this stuff. I think you can use just a relay to do this...

I'm missing the point of using the kitchen timer. You can do everything you want with just the PIC...

The point of the timer is an LCD screen and push buttons for $2 at local discount store.

I have already created one that is solely pic based, sets the camera off on intervals based on a potentiometer, from 1 to 255 seconds. I was next going to install and LCD screen with push buttons to do it all digitally, and found that the kitchen timer is cheaper than buying those parts individually.

The timer has button that when pushed at the end of the cycle, restarts the timer. Essentially, the button is connecting a pin on the CMOS to the VDD of the circuit. I may be able to use another transistor and have the timer reset itself without even using a pic...