Johansson, Theodor Final Project


 

How to Make a Wrap-Around MP3!

 

Have you ever been wearing gym shorts, and needed somewhere to put your phone, so you can listen to music? Wouldn't it be convenient if you could just strap an MP3 player to your arm and plug your headphones in?

 

 

To make this project, we're not only gonna need an MP3 player, but a casing that can be wrapped around one's arm. To protect our finished perfboard, we'll also need a secondary casing that can keep it safe. Here's a walkthrough of how to make this:

 

Materials:

 

Step 1: PerfBoarding

 

Make sure to build the circuit on a breadboard before you perfboard anything to make sure everything works!

 

This is our goal:

 

 

 

A Clever Trick:

 

 

The MP3 decoder looks wide enough to fit another IC under it, doesn't it? That's because it is! The SD card just so happens top fit almost perfectly under the MP3 Decoder:

 

 

This saves a lot of real estate for us, since we don't have to waste space on any pins that could be used for other IC's. As you can see, the only pins that the SD card uses to connect are on the female header. Mot people would flip the SD card around, or have it go off the perfboard; as for me, I prefer a clever way to save space and not risk damaging a part.

 

 

A Few Issues:

 

I had a little bit of trouble with the audio jack; I put it on the edge of the perfboard, and I needed a way to connect a wire to pin 1 on the audio jack. I ended up having to put the wire in behind the jack, but then I had to sauter a "bridge" between the pin on the audio jack and the jumper wire. This took a few tries, and caused a few problems, as you can see from my sautering job.

 

Wiring Setup:

 

Decoder  Connect
Connection
CS   --> 4050 Pin 15
SCLK   --> 4050 Pin 2
SI   --> 4050 Pin 4
SO   -->
Arduino MISO (MI)
VCC   --> 3.3V
GND   --> GND
BSYNC (DCS)   --> 4050 Pin 12
DREQ   --> A2
RST   --> 4050 Pin 10

 

4050   
Arduino 
Pin 3    --> Arduino SCK
Pin 5
   -->
Arduino MOSI (MO)
Pin 7    --> Arduino SS
Pin 9    --> Arduino Reset (RS)
Pin 14    -->  A0
Pin 11    -->  A1

*Note: Make sure that you also connect pin 1 to 3.3V and pin 8 to GND!

 

Decoder  Connect
Audio Jack               
LEFT   --> Pin 2 (TIP)
GBUF   --> Pin 1 (GND on jack NOT Arduino Micro GND)
RIGHT   --> Pin 3 (RING)

 

 microSD card  
 Connection 
MISO    --> Arduino MISO (MI)
GND    -->
GND
SCK
   -->
4050 Pin 2
3.3V+
   -->
3.3V
GND    --> GND
MOSI    -->  4050 Pin 4
CS    -->  4050 Pin 6

 

Now try to debug, and make sure your circuit functions perfectly. Also, make sure you run the Song file on your arduino so that it will actually play music in your final setup.

 

Step 2: Making the Fabric Casing

 

This is where your velcro and fabric will come in handy, not to mention your sewing skills. To get some velcro, I went down to Hasset Ace Hardware in Palo Alto, and bought myself a roll of double-sided velcro that I could sew onto my fabric casing. However, when I got to Room36, I realized that they actually had their own velcro; sticky like tape on one side, and velcro-y on the other. This ended up saving me a ton of time, since I no longer had to worry about sewing in each individual piece of velcro, and instead could just stick it on.

 

(Sorry it's sideways... I couldn't figure out how to fix that)

 

I chose a bit of black fabric that was looped around in a circle, so that I could sew the edges together and put the circuit inside. The fabric was a bit too long for my needs, so I folded a bit of the bottom up and sewed that on, so I had less length. Here's the final casing:

 

(Again, sorry about the image being sideways)

 

As you can see, I just stuck the velcro like tape onto the fabric. There is also velcro on the other side, so that it will stick when I wrap it around my arm. One side is sewn closed, and the other left open for now, so I can put my circuit inside. 

 

Step 3: Making the Protective Casing

 

To make sure our circuit is safe when inside the casing, we will need a protective secondary casing that we can fit the circuit inside before putting it in the fabric casing. To do this, I just laser-cut pieces for a basswood box:

 

 

When assembled, it looks like this:

 

 

And now we fit the circuitboard inside...

 

 

Perfect!

 

Step 4: Assembly

 

Now that you have the circuitboard in its protective casing, put that setup into the fabric casing and sew it shut. When you're done, try it out!

 

Here's a short video of my MP3 player running a sine wave test:

 

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