Crush the charcoal to a fine powder. Make a hole in the centre of the lid. Strip a small amount of insulation from the wire, pass the wire through the hole. Then place a piece of foil against the wire. Fill the lid with crushed charcoal. Place foil over the charcoal and secure with a rubber band.
+
Crush the charcoal to a fine powder. Make a hole in the centre of the lid. Strip a small amount of insulation from the wire, pass the wire through the hole. Then place a piece of foil against the wire. Fill the lid with crushed charcoal. Place foil over the charcoal and secure with a rubber band. Connect a wire to this foil. Try to get the foil under tension.
+
+
[[File:Complete microphone.jpg]]
+
+
Experiment with the fineness of the crushed charcoal and the tension in the foil. The more squashed the charcoal is, the lower the resistance. Aim for a resistance of around 3k ohms and definitely 700 ohms < resistance < 14k ohms.
+
+
Graph the resistance, pressing on the foil changes the resistance. You have built a pressure sensor. It can also sense air pressure. Change to Sound sensing. On my first try I was able to sense clapping.