Hard Drive Speaker

Many people have an old hard drive laying around. In this project we will reuse it by turning it into a speaker! While it's not super useful, it surely looks cool and people are taken aback when they see it.

You might ask yourself: how can a hard drive produce sound? There is no speaker in it.
If we take a look at the Wikipedia page, a loudspeaker can be described as follows:
When an alternating current electrical audio signal is applied to a voice coil, a coil of wire suspended in a circular gap between the poles of a permanent magnet, the coil is forced to move rapidly back and forth (...), which causes a diaphragm attached to the coil to move back and forth, pushing on the air to create sound waves.

In our hard drive we have exactly this, as can be seen in the picture: 2 permanent magnets with a coil in between; thus it can act as a loudspeaker! When we apply a current to the coil in the read/write head, it will move between the magnets and produce sound.

Now let's put this theory into practice and let's get building!

Parts

• Old harddrive (although a new one would also work :p)
• USB cable
• 3.5 mm audio cable
• LM386 audio amplifier
• 2x 1 kOhm resistor
• 2x 100 uF capacitor
• 1x 100 nF capacitor

Total cost: less than $10!

Tools

• Torx screwdrivers
• Soldering iron
• Multimeter

The first step of the build is disassembling the hard drive. Simply remove all the screws; there will probably be one under the sticker as well.

Next, we'll need to take out the guts. Undo all the screws you see and remove the components. You might have to use some force to remove the magnets.

We only need to keep the read/write head and the magnets, the other parts can be thrown away. Therefore, the ribbon cable attached to the read/write head can be removed.

Prepare the voice coil

The first thing that we will do is connect 2 wires to the coil of the read/write head. It is easiest to solder the wires while the head is removed from the case. It can then be reinstalled together with the magnets.

Make an amplifier

We now have a speaker, but we still need an audio source to drive it. The output from a headphone jack is not powerful enough to drive it, so we'll make an amplifier to fix that.

The circuit of the amplifier comes from Afrotechmods, an awesome youtuber; his video can be found here. Check it out for an in depth explanation, I'll stick to a short version.

The heart of the circuit is the LM386, an audio amplifier chip which will do all the hard work for us. It takes the audio signal from our audio device as an input and drives the speaker.
While the input signal should be Mono, the 3.5 mm headphone jack outputs a Stereo sound. A conversion is necessary, and accomplished with the two 1 kOhm resistors.

Solder everything together according to the schematic and attach the speaker. You might need to use some sandpaper to remove the coating on the headphone wires. The power will be provided by the USB.

Mounting

Now that our amplifier is fully functional, all that's left to do is mount it in the case.

You can use some double sided tape, velcro, or drill a hole in the PCB and mount it with a screw like I did.
Route the cables through the hole in the casing and secure them with a zip tie to finish it all off.

We're done! The only thing left to do is to test our new hard drive speaker.

Connect it to a USB port and an audio device, crank up the volume and witness the magic!
I hope you liked the project and have found a good use for that unused old hard drive!

Feel free to check out my other instructables:https://www.instructables.com/member/ThomasVDD/