Matchbox Microphone

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Introduction: Matchbox Microphone

How to make a really basic microphone out of a matchbox and pencil graphite. This simple electronics experiment demonstrates how a microphone works and the science behind it. We'll explore the fundamental principles of a microphone and build our own working model.

Step 1: Background

A microphone is a device which converts acoustical energy known as sound waves, into an electrical energy know as audio signal. Inside the head of a microphone you will find a diaphragm, this is a thin piece of material which converts sound waves into an audio signal. When the diaphragm is hit by sound waves it vibrates, and its these vibrations which are converted into electrical energy known as audio signal.

Microphones are used in a wide range of applications including telephones, computers, hearing aids, megaphones, music recording and surveillance.

Step 2: Getting Started

What you need:

  • A Matchbox
  • A Pencil
  • Scissors
  • Crocodile Clips
  • Leads
  • A 9v Battery
  • Some Old Earphones
  • A Sharp Knife
  • A Cutting Board
  • Speaker Wire

When you have everything you need, go ahead and follow the instructions or watch the video for a visual demonstration and full instructions.

Step 3: Building Our Microphone

Take an empty matchbox and remove the drawer. Then using a sharp pencil poke two holes through each end of the drawer, as shown in the pictures.

Step 4: Remove the Pencil Graphite

Use a sharp knife and a cutting board, to carefully split your pencil in half and remove the graphite.

Step 5: Grinding a Flat Surface

Take a pair of scissors and carefully run the blade up and down the length of the graphite to create a flat surface on one side.

Step 6: Assembling the Microphone

Insert the graphite into one of the holes in the matchbox drawer, and out through the hole opposite, as shown in the picture. Snap the graphite off so it sticks out roughly 1cm each side of the matchbox.

Put the remaining graphite through the holes in the other side of the matchbox. If you haven't got enough graphite, extract some more from another pencil in the same way we did earlier.

Twist the graphite so the flat surface we made is facing upwards.

Snap off another short piece of graphite, and place this flat-side-down on top of the two pieces in the matchbox as shown in the pictures. This piece will act as our microphone diaphragm, and the reason we made the flat surface on the graphite, is to stop it rolling around.

That's our microphone completed.

Step 7: Wiring the Circuit

We're going to power the circuit using a 9v battery, and we'll monitor what sounds the microphone captures through a pair of old earphones. The battery will create a current around the circuit and the microphone will capture sound waves and convert them to an audio signal, which we should then be able to hear through our earphones.

Take your 9v battery and an old pair of earphones that don't matter if they get damaged, (mine came free with an old mobile phone) you could use an old speaker instead. Then using a selection of leads and clips, connect one battery terminal to one side of the microphone (the red lead in my pics), and the other battery terminal to one channel of the earphone jack (the black lead in my pics). Connect a third lead (the yellow one in my pictures) between the other side of the microphone, and the tip of the earphone jack.

If you're using stereo earphones like me, you'll only get sound out of one side, connect the leads to the earphone jack as shown in my pictures.

Step 8: Testing the Microphone

To see if the microphone is working properly put your earphones in, and try gently tapping the matchbox. You should be able to hear it through the earphones.

Step 9: Extend the Range

To really test out how well it works you need to be in a different room, so you can only hear the sound captured by the microphone and not what your own ears are hearing at the same time. To do this take a roll of speaker wire and extend the circuit. Disconnect the earphones from the circuit and attach the clips to the speaker wire instead as shown in my pics. Then run the wire through to a different room, you can even go upstairs to the other side of the house if your wire is long enough, then use another couple of leads to reconnect the earphones again as show in the pics.

Now get an assistant to talk into the microphone, it will be a little crackly but you should be able to hear exactly what they're saying.

If you build two of these the same you can make your own two way communication system and chat to each other.

This is a great fun science experiment to do with children learning about electronics. It helps develop a good understanding of a simple electrical circuit and demonstrates the basic principles of a microphone. Being able to build your own microphone which works out of household items is fun, educational and rewarding.

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75 Comments

Would have made a better science "experiment" if the underlying physics had been discussed. These do not operate on quite the same principal as a standard diaphragm mic (the diaphragm part, at least).

3 replies

could you comment on the underlying physics of this? I couldn't figure out how it worked.

this is simply harmonic motion vibrations (which you studied in class 12th)

the varying pressure in air vibrates the graphite lead up and down also rotate slightly and causes change in resistance.

due to change in resistance potential drop on the speakers changes hence pressure variations are converted into electric signals(waves).

I'm asking about this matchbox mic.

Will it damage headphones? Just wondering

Can you hot glue the pieces of lead, or would it just not work? Because then you could hold the mic without the smaller piece of lead falling out.

I am an elementary student and Im graduating this year. I would like to ask if how much hz it has when i plug in earphones? ow much hz it has when i plug it in speaker? just asking for the preparation for our science fair..thank you for the idea..your genius...

hello,

can someone please say me some more applications or its usage and hence its respective procedure?

could this also work for a speaker or would i need more power?

3 replies

Yes you can but you need more power

but it did not work without crocodile clips

Yes you can as it is also a conductor of electricity

why did you write it twice???????

For those of you wondering, you can use metal instead of pencil lead. I've been experimenting with two paper clips as the connections and different materials as the free-floating part, and have found something that should be discussed. I first tried 3 paper clips stripped across the bridge, with 4 AA batteries hooked up to it in series. I could only hear loud bumps and buzzing. After experimenting and reducing to two AA batteries and only using 1 paper clip, I found that if I talked very quietly, I could hear what I said - but it was still bugging out my headphones. I then attempted a piece of aluminum foil folded accordion - style. It was so loud that it made loud bumps on my headphones and hurt my ears. The reason graphite doesn't do this is because, though it conducts electricity, it acts as a resistor; as in, it makes it much harder for electricity to flow through it.

In conclusion, to use metal instead of graphite, you will either want to hook up a customized circuit to reduce the current, or, for those of you who can't, if you use a 1.5v AA battery with two paper clips as the connections and a paper clip across the middle for the actual microphone part, using a 200 ohm resistor (Or 220 ohm resistor) hooked up on the positive lead of the battery will bring the amps down to 7.5 amps, (or 6.8 amps) and will hopefully prevent your headphones or speaker from blowing out.

SERIOUS NOTE: I am still new to calculating resistance, and this is all theory until I have a chance to actually get some resistors, so use headphones that you don't care whether or not they are destroyed, and DO NOT PLUG INTO AN ELECTRONIC unless you are ABSOLUTELY CONFIDENT that it is safe, or else you may just ruin ports on your computer or other device. Hope this helps!

1 reply

lol I found a plastic battery case from a metal detector to use for this experiment that held 3 aa batteries and when i used metal i ended up melting the case because the electrical discharge ended up becoming stonger and hotter.

a small speaker

cant we fix the the 3rd lead