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Johansson, Theodor Final Project

Page history last edited by teddyjo@... 5 years, 1 month ago


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:



  • 1 bread board
  • 1 perf board (you'll probably need more than 1 though; mistakes happen)
  • 1 Arduino Micro
  • 1 MP3 Decoder
  • 1 4050 Voltage Divider
  • 1 SD Card (with header pins soldered on)
  • Female Header Pins
  • Solid-core jumper wire
  • Velcro
  • Cloth/Fabric for the casing


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
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


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  
MISO    --> Arduino MISO (MI)
GND    -->
4050 Pin 2
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...





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:


Fliqz has shut down their service. To access this video, email support with this video id: aca0f362dc9f40c6a8925c6dd0212c6a



Comments (1)

praveen2@... said

at 12:35 pm on Aug 18, 2015

Dear Johansson,

Congratulations on accomplishing your final project goal. We appreciate your caution in choosing a low risk and pretty doable project. We appreciate your efforts to make a hand glove and fitting the MP3 inside a box before putting it into glove. We liked your idea of placing SD card below the decoder to save space.

We wish may be could have done better documentation. Your documentation lacks your code, future prospects of your project and conclusion. The video is playing sine test so we assume your final MP3 song is not playing on the perfboard. we would love to see your final video with your hand glove to see how it is working, but it is missing in the documentation.

Currently, your project is mostly lab6 MP3 player packed into a hand glove. it would be quite interesting to see if you tried to attempt a little extension beyond lab6.

However on over all, you did a good job attempting to accomplish your project goal with in a very limited time. We really appreciate your effort and we hope you continue building fun electronics.

We wish you good luck with your career endeovers.

Best regards,
Praveen, David, Dongao, Samyuktha, Tian, Xiangyu, Zahra

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