Sending Sound Electronically

Building a pencil lead

microphone

Equipment

• 9v battery• 3 lengths of pencil lead (graphite core of

pencil or refills for mechanical pencil)• 2 crocodile clip wires• Ruler• Pencil• Old/cheap earphones• Small box such as matchbox

To build one microphone you will need:

Step 1

1. Measure the across the narrower width of your box.

2. Break off two pieces of lead which are each 2cm longer than this.

3. Use the edge of your ruler to very gently scratch along the length of the lead so that the two pieces have one flat ridge along their length.

Step 2

1. Use a pencil to poke two holes in the side of the box. Make sure that the holes are evenly spaced apart on the side of the box and the same height from the base of the edge of the box.

2. Repeat this for the opposite side of the box trying to place the dots in equivalent positions.

Step 2 continued

3. Gently push the pencil leads through the holes from one side of the box to the other, so you end up with two parallel pencil leads in the box with 1cm sticking out either side. Twist the leads so the flat side faces up.

Step 3

1. Break a piece of lead which is wide enough to lie across the two pencil leads in your box.

2. Very gently use your ruler to scrap along the edge of this pencil lead to once again to make a slightly flatter surface

Step 3 continued

3. Lay the this piece of lead across the two parallel pieces of lead. The flat side should like across the other two flat sides so it doesn’t roll around.

Wire setup for microphone

Step 4

1. Wire up your microphone according to the diagram.

2. Make sure that one of your crocodile clips is attached to the very tip of the audio jack of your earphones and the other one is attached to the base or the piece of the metal jack closest to the wire.

Test the microphone

Step 3 Wire up your microphone.1. Finally have a go gently tapping your microphone

and see if you can hear a noise through the head phones

2. Because the earphones will be stereo you will only hear noise from one side of the earphones.

3. If use additional crocodile clips and a long wire you can test the microphone across a distance or from another room.

4. Can you think of any ways you could improve the performance of the microphone?