Here's a great demonstration of how a motor can be used as a speaker for less than 5 dollars. It took 5 minutes to put this whole thing together, without soldering a thing!
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Step 1: Materials
Materials and tools used to make this:
(1) LM386 Chip from Amazon
(1) Breadboard from Amazon
(1) Slow motor, got mine from an old printer
(a couple) alligator clips and jumper wire
(1) Cheap earbuds
(1) Multimeter or continuity tester
(1) hobby knife
(1) wire cutter
(1) piece of fine sandpaper
(1) Something to play music
Step 2: The Schematic
Here's a schematic so that it's easier to follow along. If you don't know what a schematic is it's basically like a little map of electronics that tells how things are connected. The big rectangle thing is the chip, and the rest is pretty self explanitory.
numbering of pins on the 2nd picture
Step 3: Prepare the Earbuds
Cut of the ear bud part leaving you with the audio jack part
Step 4: Strip the Wires
Using a Hobby knife (careful, they are very sharp!) cut through the rubber insulation on either the left or right side (doesn't matter, we only need one)
Once you cut through the insulation, use some fine grit sandpaper to uninsulate the 2 fine wires.
Step 5: Lable the Wires
Using a continuity tester (testing if 2 things are connected) place one end on the jack (see picture) and the other on one of the wires. If they are connected then then we'll call it audio negative, if not connected we'll call it audio positive, and the other wire is audio negative
Step 6: Insert the Chip
Insert the LM386 into the center of the bread board, so that no pins are connected. You might have to push the pins in a little to make them square.
Step 7: Connecting the Audio
Since the audio wires are really thin, we need to use a jumper cable (any thick wire that fits in the bread board will do) and alligator clips. Insert a jumper wire into pin 2. Insert another one into pin 3. Attach an aligtor clip to each wire. atach the Pin 2 to audio + and Pin 3 to Audio -.
Step 8: Add the Motor
Attach a jumper wire to pin 5, along with an alligator clip to the motor. you can then attach the other end of the motor to the - of you battery. You can now also attach pin 4 to the - of the battery using the wire and alligator clip.
Step 9: Prepare for POWER
attach a wire and clip to pin 5. You are going to be connecting this to the+ of the battery.
Step 10: Hook Up Some Music and Listen to the Motor!
Plug in an MP3 player and attach the clip onto the + of the latern battery. If you got a slow motor you should be able to here the music if you put it on a solid surface such as a table.
Step 11: Care for a Listen?
Step 12: How Does It Work?
Speakers work by pushing a cone up and down at different speeds (frequency) vibrating the air.
Here's a video to explain it: http://electronics.howstuffworks.com/speaker.htm
This motor speaker works by vibrating material around it by changing the speed (every so slightly) that the motor turns.
Have fun with your motor speaker!