Very often electronics technicians have to find out the value of a capacitor. This Project will let you determine the value of a capacitor by sound.
Connect a capacitor to the two long wires. Press the Key and adjust the Control Knob until you get the least volume in your Earphone, Disconnect the capacitor. Note the setting of the Control Knob.
Now measure some capacitors whose value you do know. Compare the Control settings you get measuring known capacitor values with the setting you get measuring the unknown value.
In this way you can get a fairly accurate idea what the value of the unknown capacitor is. Make a chart or graph of the Control settings at different known capacitor values. In this way, you can use this circuit to test other capacitors whose values you're not sure of.