ELM - MP3 Player

Nov 7, 1999
Update: May 2, 2000

Pocket-Sized MP3 player

The MP3 player is a new kind of portable audio player. It will be shipped simultaneously from many audio makers in the early part of 2000, and will start a new generation of portable audio. I have omitted a general description of the MP3 player and format because it is public knowledge.
Well, I built an MP3 player. Let's build something in fashion like that. I aimed to build it small as such as it can be called pocket-size.
I chose an MP3 decoder (key part of the MP3 player) taht was found at the parts shop Wakamatsu Tsusho in Akihabara electoric-town, Tokyo. The player also uses an "Atmel AT90S8515" as a system controller, and SmartMedia as data strage.

KEY SPECS

Main LSIs	MCU: AT90S8515 (ATMEL) DSP: MAS3507D-D8/-F10 (MICRONAS INTERMETALL) DAC: DAC3550A (MICRONAS INTERMETALL)
Recording media	SmartMedia (NAND type flash memory card) Capacity: 8MB, 16MB, 32MB, 64MB, (128MB)
Audio data format	MPEG1/2/2.5 - L2/L3 (depending on the specs of MAS3507D)
Control buttons	PLAY/PAUSE, STOP, NEXT, PREV, VOL+, VOL-
Track management	All interaction, such as transfer audio data, delete track, format medium, etc..., is controlled with a PC via an ISP cable.
Dimensions	90mm(W) x 70mm(D) x 23mm(H) Weight: 97g (excludes battery)
Power requirments	2 x AAA type alkaline battery External DC power supply: 2.0-3.5V
Power consumption	Playing: 310mW (210mW if used -F10 version). Pause/Online: 75mW Standby: 0
Cost	8,000-9,000 JPY (excludes memory card)

The table to the left shows key features into the built MP3 player. For "play" mode, the player is controlled with six buttons and supports only minimal functions.
For the removable media, it uses SmartMedia, which is the most popular memory card for digital cameras. The cards will not be compatible in other equipments because the SmartMedia is formatted in local format when use on this MP3 player.

HARDWARE

Parts Side | Solder Side | QFP on the board
Block diagram
Main board circuit diagram (Mar.10, 2000)
Optional poewr supply and charger
Parts list

Circuit Diagram

The circuit for the MP3 player is composed of three LSI chips plus capacitors, resistors, switches, etc. The DSP decodes input MPEG data and output as IIS digital audio data. While the DAC converts IIS data from DSP to an analog audio signal. The micro-controller controls all of components, such as the other LSI chips, SmartMedia and data flow.
The circuit diagram of the MP3 player is very simple. However, the same can be said of the manufactured MP3 players. Actually, most manufactured MP3 players are also cheaply designed, and add a LCD at the best. They are expensive in that they have built in or attached "memory".
The MAS3507D includes a step-up DC-DC converter. Therefore, it can produce constant voltage without external DC-DC converter from variable voltage such as batteries. It seems the MAS3507D is designed for portable use such as MP3 players. In this player, step up to 3V from 2-3V input voltage for the system power.
This player doesn't have a power switch, instead, the PLAY and STOP buttons serve as the power switch. The PLAY button is connected to power holding circuit. When the PLAY button is pressed, Q1 will be turned on and system powered up. Q1 will be kept by the micro-controller after the PLAY button is released.
P4 is a pin header of six pins and is an ISP connector for the AVR. This connector will be used to program the firmware, and for communication to the host to transfer the sound data or control of the player.
P2 is an interface connector for the memory cards. It is designed to connect directly to SmartMedia, however, I think it can connect to any strage device that works as an MP3 data source such as CompactFlash, MultiMediaCard or PC (LPT port). Of course, the firmware and circuit diagram must be modified when connecting any other device.

Building a main circuit board

The upper right image shows the main PCB. All LSI chips are QFP to keep the design small and pocket-sized. Also, pin converter boards were not used for size, the QFP LSI chips where directly mounted onto the universal board.
First, put a polyimide tape on the PCB as a mount base. Then bond each LSI onto the tape. And the directly wire to each lead of the LSI with #30 UEW. Polyimide has very good heat resistance, it will not melt or burn at soldering temperture.
The capacitors and resisters are chip type, and they are mounted on both surfaces of the circuit board. Mounting only single surface is not good, it should be used both surfaces to mount the parts when use a double surfaced universal board.

Building a memory card socket

This was most difficult part because I could not find a socket for the SmartMedia at the market.

Therefore, I built it my own (right image shown). However, it could be built with the materials found in my junk box and I could build it smaller than any other sockets :-).
Now, the memory card socket seems apper on the market.

Audio characteristics

I measured the audio characteristics of the MP3 player with an audio analyzer. Here are the results:

The SNR (signal to noise ratio) is 92dB. Very good considering this is a portable MP3 player!
The THD (total harmonic distortion) at 1 kHz is 0.06%. Not too good :-( It may be due to MP3 compression.
The kind of the MP3 encoder affects THD. Most free encoders cannot generate MP3's with good quality. The 0.06% is a THD when measured with an MP3 file genereted by Fraunhofer's encoder mp3enc.exe, 0.09% or above with any other encoders.

One cell operation

When use the F10 version of MAS3507D, it can also operate with only one cell of AA type battery. If you wish to build as one cell operation, change parts value as follows:
R3: 47
R10: 22k
R11: 10k

FIRMWARE

This player works in two different operating modes that called Stand Alone Mode and Online Mode.

Stand alone mode

Normaly, the MP3 player operates in this mode, which is a generic portable audio player. All tracks will be played in an infinite loop. This player includes minimun funcitons so that track jump or volume can be adjusted with only six buttons.

PLAY/PAUSE button
This button turns power on and play is started. When pressed this button during play, the player will enter pause mode. Pressing the button again will resume play. In pause mode, any other button operation will also be accepted.
STOP button
Stops to play and turns off power.
NEXT button
Jumps to the next track. Next to last track, it returns to the first track.
PREV button
A single click will jump to start of the current track. A double click, or more, will jump to the previous track or tracks. Previous at the first track will go to the last track.
VOL+ / VOL- button
Changes volume setting, which will be stored in EEPROM when power is turned off.
Resume mode
When the STOP button is pressed for one second, playing information, such as current track number and time, will be stored in EEPROM. At this time, a confirmation beep is sounded and power is turned off. This information will be read back and playback will be resumed. If STOP button was press and released within one second, or the SmartMedia has been changed, the resume information will be destroyed and playback started from the first track.
Power monitor
This is an important capability for battery powered operation. In stand-alone mode, input voltage is always monitored by firmware. When input voltage dips down below 2.0 volts, a warning beep and LED blink indicate low battery. Below 1.8 volts, power is turned off with resume mode.
LED indicator
The LED indicates play back state in addition to being a power indicator. During play, the LED is lit continuous. When paused, the LED blinks slowly. If the battery is low, the LED blinks quickly (it overrides paused).
BEEP
When playing:
Any button operation: "Pi"
Detect low battery: "Pu-Pu-Pu-Pu-" --> LED blinks quickly
When power is on:
No track: "PuPu" --> Shutdown
Unformatted: "PuPuPu" --> Shutdown
Invalid Medium: "PuPuPuPu" --> Shutdown
Track information
Track information can be monitored from a PC with an ISP cable and its switch is OFF(disconnect controls). The Player sends track number and ID3 tag(if exist) when a track is started.

Online mode

Power is turned on with the PLAY button. When an ISP cabled is attached to the ISP connector (MOSI is pulled low) the player will enter Online-Mode. The monitor program can then be started on the host PC.
In Online Mode, operations such as format a card, write sound data, delete a track and other opereations are done online commands.

Example of the monitor screen
Connects with an ISP cable, serial data format is N81, 38.4kbps. The terminal program must be running before player powered is on. If not, ER signal will not go high, and the power switch will not be held because reset will not be released.
When adding a track, MPEG data is transferred with fast synchronous mode. It is recommended that a DOS terminal program be used (provided later on this page). Transfer speed in synchronous transfer is between 25KB/sec throuh 35KB/sec.
Descriptions of the monitor commands are as follows:

L command
Show track list, size in KB, play time, bit rate, sampling rate, channel mode and ID3 tag(if exist).
W command
Add a track in synchronous transfer. When this command is issued, player will send a data request message, and then suspend to the command shell, start MPXFER.COM with a filename to begin transfer. The control tool also can automaticaly execute these instructions with a short cut key.
P command
Play back a track. To stop playing, type any key.
M command
Change track order.
D command
Delete a track.
DA command
Delete all tracks and clean-up lost chains due to transfer error.
FM command
Format a medium. New memory cards must be formatted with this command. Other commands except R command cannot be used to unformatted cards.
R command
Read page data from memory card and display it in dump list. Page number is input in hexdecimal. This command was implemented for debugging, not for normal operations.

To program firmware

Firmware (hex file) is programmed with AVRSS.EXE via an ISP cable. To program the firmware, power on by pushing the PLAY button. Of course, the PLAY button must be held down until end of programming because controller cannot hold the power state while in ISP mode.

SPECIAL ATTENTIONS

This MP3 player doesn't support specifications of the SmartMedia standard. This player is using the memory card in local format. If a memory card is formatted with this player, it will be unusable on other equipments.
The design of the memory card socket does not allow for hot-plugging. Be sure that the power is turned off when inserting and removing a card. If a card is inserted or removed while player power is on, the card or player could be damaged.

TECHNICAL DATA

MP3 player block diagram
MP3 player circuit diagram
Power supply and charger
Parts list
Latest version of the firmware (R0.91c) containing source files
Control tools (Feb 16, '00)
Building an ISP cable
Link to the Micronas Intremetall