Make Credit Card Size MP3 Player, Just Simple!
This MP3 player is based on MicroChip's ATtiny44 (or PIC16F688) MCU, plus the decoder, VS1011e.
Specs and Features:
. On-board controller: PIC16F688(4KW flash ROM and 256 bytes RAM) from MicroChip, or ATtiny44 from Atmel.
. MP3 decoder: VS1011e (SOIC-28 version), from VLSI, Finland. It combines MPEG decoder, DAC and audio amplifier to drive earphones.
. SD memory card: FAT file system. Only 1 level sub-directory supported so far by the on-board controller.
. Support up to 320Kbps bit-rate, 44K sample rate MP3 files.
. Very good audio output sound.
. On-board three buttons that control the operation of the MP3 player (power On/Off, volume control, MP3 file switch.
. A DC/DC converter chip (REG710) is used to supply the power (2.7v or 3.0v). No inductor used in the design.
Schematic of the MP3 Player
Mp3 Player Assembly Kit:
The kit comes with all the parts except:
1) Battery holder (AAA x 2) not included. It can be purchased at your local store (e.g. Radio Shack);
2) SD flash card not included. It's suggested to use a micro-SD card, plus an SD TF (SD adapter) socket, as shown below.
 there are two surface mount devices, dc/dc converter (in SOT23-6 package) and the decoder vs1011e(SOIC-28 package), that come with the kit. They should be installed first. Please pay attention to their pin direction against PCB layout.
 Resister R5~R8, plus R2 and R11, may form an SD card holder to hold an SD card in place. You can use some very thin bronze spring wires to make the connect pins. The pictures bellow show a simpler and easier way: use an SD TF socket. That means, you can use some thin wires to connect the TF socket to the PCB board on the back side, and put a piece of double-sided tape between the socket and PCB to hold the socket in place. In this way, you just leave the socket on the board, and plug in & out the micro SD card.
How to Operate the MP3 Player:
The kit will be programmed with a FW when shipped. There are three buttons (PLAY, UP, DOWN) that are used to control the operation of the MP3 player.
(1) Push 'PLAY' button to turn on the player. Then, at normal situation, the on-board LED(D1) will flash at 'fast' frequency (4Hz) that indicates it's search MP3 files in SD card.
(2) When the searching is done, the LED will stay ON, indicating (certain) MP3 files found, and ready to play.
(3) Push 'PLAY' button then will play (the first) MP3 file. Or Push 'UP'/'DOWN' button to switch MP3 files (forward/backward).
(4) When playing an MP3 file, LED is in 'slow' flashing mode(2Hz), 'UP' and 'DOWN' buttons are used for controlling volume at the moment.
(5) When playing an MP3 file, 'PLAY' button is used for pause/re-play. When in pausing, 'UP' and 'DOWN' are for switching again.
(6) Any time when 'PLAY' button is pushed and held for more than 1 second, it will turn off the player.
 Only support regular (micro) SD, not SDHC, card with memory size no more than 2GB.
 The (micro) SD card should be formatted in FAT(16), instead of FAT32, and only 1 level sub-directory supported.
 The on-board USB port is for battery charge, as shown in the schematic, not for file transfer.
Credit Card Size MP3 player kit: $22.00/each, plus $3.00 S/H fees.