Q:

Switching Piezo Buzzer with a Transistor

I want to be able to switch a piezo buzzer with arduino without connecting it directly.
I have wired the following circuit I found on the internet:

The problem is that the voltage across the buzzer is very low (lower than 1v when I connect a voltmeter instead of the buzzer)
My guess is that I lack some basic understanding of how transistors operate. Maybe I chose the wrong transistor or I need to apply higher voltage between emitter and collector?

A:

Make sure that the GND connection at the emitter of the transistor also connects back to the GND of the Arduino board. 
Check that you have the diode installed the right direction. If the diode has a line or band marked end that side should be connected to the +5V.
Normally you would check the voltage when the buzzer is in place instead of removing it. Since you removed the buzzer and measured less than a volt it is an indication you have the diode installed backwards.
If you had the diode installed backwards replace your transistor with a new one. You likely damaged it.

