This is a very simple carbon mic, but if it is carefully constructed, it will pick up louder sounds fairly well. You need:
Saw the battery carbon in half lengthwise. Sand the flat sides smooth. Drill holes through one end of each about 3/8" (10 mm) from the end to accommodate a screw, and lightly drill a shallow dimple in the flat part of the other end of each, about 1/4 " (6 mm) from the end. Mount the two halves at opposite ends of the small wood block, about 2" (50mm) apart, so the flat sides face each other. The pencil lead is placed in the dimples, spanning the two. It should be sharp at both ends, and should fit so that it can move slightly (but not to loose). It is this loose contact that is effected by whatever sound waves pass through it. Mounting the assembly to a wooden cigar box isn't essential, but it does help to amplify any sound vibrations. Mount the entire thing to some stable base. Connect one terminal of the battery to one of the carbon elements, and the other to one terminal of a headphone (or amplifier). Connect the other terminal of the headphone to the second carbon element. After trial and error, it will pick up sound and other vibrations.
- carbon from a C or D carbon battery
- carbon from a pencil
- cigar box or other suitable sounding board
- battery, 6 volt
- block of wood , app. 2" x 3/4" (50 x 20 mm)
- wood base