transistor issue???

[Shawn Northrop]

I am trying to modify a circuit to use a piezo buzzer as a trigger. The first circuit i attempted worked. I attached a transistor and the buzzer as shown in the picture:(The black and Red horizontal lines at the top are coming from the circuit)


Everytime i flicked the buzzer the connection was temporarily made.
The second circuit i am trying to modify i attached the buzzer and transistor in the same way. This circuit does not work however. I used a multimeter and found the first circuit has about 4v traveling through the transistor where the second only has <1v. Also the first circuit is powered by a 9v battery where as the second is plugged in to the wall with a 9v DC.

I am fairly new at this so any information or suggestions would be appreciated
Thanks,
Shawn

[Ge_Whiz]

It all depends on whether the transistor in your piezo trigger gets a suitable DC bias across it when you connect it. 4V is fine, 1V is not enough. In your second circuit, identify the +9V line and connect it via a 47k resistor to your transistor collector. Then take the trigger signal from the junction of the resistor and the collector (i.e. connect directly to the collector lead and your trigger should now work. You may need to play with the resistor value, and your mileage may vary depending on what you're connecting to.

[Shawn Northrop]

Is this what you mean:


If so i think the buzzer will be buzzing which is a problem for me.
Also if the connection on is meant to pass <1 v and it passes more could this be bad?