Volume Level Meter
Sometimes we need some way to measure the output of an oscillator or other device. This Project takes the AC output of an oscillator or other device, rectifies it and indicates the output on the Meter.
You can connect the output of an audio oscillator to Terminals J1 and J2 and measure it. You can also connect the Speaker in place of Terminals J1 and J2 and use it to measure the sound of" your voice, the TV or a radio. (This is similar to Project Electricity from Sound in Electric Power Section)
You can adjust how far the Meter swings by using the Control Knob. Try adding the Key and 3 volts of electricity to this Project in place of Terminals J1 and J2. Try pressing the Key and releasing it rapidly. What happens to the Meter? Can you guess why? (If you can't, take a look back at Project An AC Simulator in Transformer Sectin and the notes you made for it)