Fresh Breath, Fresh Tunes, Fresh Design

Tired of not being able to find cases for your projects? Stuck with those hideous ABS plastic RadioShack boxes? Try those ubiquitous tin boxes, not only do they block EMI, they come with free mints! Fresh breath and fresh design in one.


The Minty MP3 player can be built from parts that are sold at Ye Olde Traditional electronics distributor (digikey/mouser/newark). Half of the parts can be sampled for free, for a minimal total cost of $25 for parts, and $25 for a PCB. And the case is soooo Minty!*

* Do not eat MintyMP3

Fresh Breath and ATA+FAT16

Works with your favorite compact flash card, currently in trashy-revision v.1 mode. Amaze your friends! Upload files via stunningly slow 115kb/s. Or cannibalize the code for FAT16 handling (create/delete/read files).


Unlike some other mp3 players, this one comes with a 3.3v boost regulator (for running off of 1 or 2 alkaline or rechargeable batteries) and an FM transmitter, for when you're on that road trip to Canada and you forgot your #@&*ing tape-adapter dongle thingy. Also, a really cool volume control button.

The MintyMP3 hardware is a standard mix of high power 8-bit microcontroller and ASICs. A single PIC18LF452 running at 20mhz (For v2 the crystal has been changed to 29.4912MHz) with the minty firmware talks to the CF flash card, navigating the FAT16 file system and loading mp3 files, then sending the data to the STA013 MP3 decoder chip. The STA013 decodes MP3 into digital audio which is then converted to linelevel audio by the CS4340 DAC. There is also a MAX576 boost regulator (optional if running from a LiIon battery) and a MAX2606 FM transmitter (optional).

Everything on the board runs off of 3.3V (3.0-4.0V is ok so it can run directly off of a LiIon) don't even think of running it at 5V!


The microcontroller is PIC18F452 (in particular, the 18LF452, which can run at 3.3V), the 'really nice' PIC. Lots of RAM/ROM and can run a bootloader. The PIC reads and writes the compact flash card (for playing mp3s and uploading/deleting mp3s), reads button presses, and configures/runs the STA013 mp3 decoder chip. It understands the FAT16 file system format, although it ignores long filenames. The best way to use it is to program it with a bootloader, such as the tinybld'r, and then upload new firmware as desired through the serial port. Using a bootloader is much faster and doesn't require a PICStart/ICSP programmer.

MP3 Decoding Chip

The MP3 decoder chip I used is the STA013, which is the only one I could find to purchase easily (going rate is $12) in the US (Mouser sells it and Digikey carries the more extensive STA015T which also does MP3 encoding, PJRC also sells it for a very good price. Also FutureLec has it for a paltry $7!)

The MP3 chip is controllable via an I2C port, to set the volume/bass/treble, upload new firmware, get the current mp3 data, start/stop etc. It then signals that its ready for mp3 data by pulling the MP3REQUEST line high, after which the microcontroller sends the file to the STA013 via SPI.

A lot more information is available from PJRC's 'how to use the sta013' page. This is a strictly 3.3V chip.

I didn't use the VS1001K or MAS3509/MAS35x9 because they were not as easy to get.


For a DAC I use the CS4340, which you can buy from Newark for $2.50. They make up for it by charging $12 shipping. I would highly suggest that it get replaced by something like the $2.70 PCM1748 stereo audio DAC, which is carried by Digikey or can be sampled for free from TI. (So, I haven't gotten off my ass and actually figured out how to replace the CS4340 with the PCM1748, it has a different pinout and I'm lazy. Feel free to make the change and send me the update!)

If you want to drive headphones instead of line out, I wouldn't use the cap/resistor values in the datasheet, since they seriously attenuate the signal. Try 10 instead of 560ohms and a beefy 33 or 47uF cap instead of 3.3uF to keep realistic 3db cutoffs (see the PCB schematic).

Or better yet, measure the capacitors and make sure that the low -3db point is ~120Hz and the high -3dB point is >>20kHz

Compact Flash Storage

My digital camera went bust so I had an extra 128M compact flash card. The nice thing about CF is that it's pretty damn cheap (you can get a 512M card from for $50). Cheaper & faster than multimedia cards (MMC) and can be accessed via a PCMCIA slot, as all PC laptops have, using a $5 adaptor (although you can read/write using the Java program MintyComm program talking through the serial port).

One nice side-effect of using CF cards is that they 'talk' ATA so it's easy (design-wise) to swap it with a full IDE drive in case you ever need to access a large amount of data (a car mp3 player?)

DC/DC Converter

In case you want to run this off of 1 or 2 alkaline/rechargables there is a DC boost regulator on board, the MAX756, which will step up a 1V supply to 3.3V @ 300mA. A little pricey at $5 from DigiKey, but you can sample them for free from Maxim's website. Theres even a 'low battery' indicator but it seems sort of counter-productive to burn more power through an LED.

FM Transmitter

I hate not having an audio cable to hook up a player to a car, so instead, I put the incredibly cool MAX2606 (only available in low quantities by sampling) all-in-one FM transmitter chip in. Wow! Very low power only a few mA, so I didnt even put in a switch for it.

USB Interface (New for V2)

A USB to serial chip (the FTDI232BM) and li-ion battery charger chip (MAX1811) means you can plug Minty into USB and upload/download files and recharge your battery, sweet!
The Minty Firmware is the software burned into the PIC microcontroller and which does eveything but decode the mp3's themselves. The code is divided into subsections: the menu system for debugging/MintyComm interaction, the Compact Flash controller, the FAT16 decoder & file reader/writer, the MP3 play loop, the button query procedure and STA013 initialization and configuration.

It's written in CCS PICC, which means its very portable and can easily be recompiled or translated for other microcontrollers. If you don't want to pay for the compiler, I include the HEX firmware file and asm file.

All of the code is written by moi and is published under the MIT license, which is a derivative of the BSD license.


This file contains basic constants like the crystal frequency (20MHz recommended), the serial speed (115kbps will make file transfers just barely reasonable.) It also has the pin assignments. So if you want to change the hardware around I'd peek here. Make sure that the firmware version matches the hardware version or you are majorly bummin'.

byte buttonquery() checks the buttons and returns a value corresponding to whether any are pressed. For some reason I haven't determined, button 3 doesnt work. It might have something to do with the fact that I'm sharing that pin with the UART. Theres a timeout to reduce button bouncing (100ms for volume change, 250ms for track change.)

void convertToFATName(char *name) takes a 8.3 format name and makes into an 11 character name as FAT understands them.

boolean processCommand() runs a menu that will test the various aspects of the card, to get to it, strike a key during the "waiting for char" part of the booting process.

void main() sets up the chip, turns off the ADC, turns on the timer #2 interrupt, configures the ports, boots up the hardware, and resets the volume. It then waits for 3s to hit a key and go to the menu or else just starts playing through all the files in the root directory. It also handles next/prev track requests.


This file contains the bitbanging and manipulation of the Compact flash card, below the level of FAT format. The card is used in 8 bit mode, 8 data lines, 3 address lines, and a few manipulation lines.

boolean is_CF_Out() checks the CF_CD (card detect) line, which is pulled low whenever the card is inserted

void CF_SetAddr(byte addr) puts the bottom 3 bits of the byte onto the addr lines to the CF

void CF_TaskFileWrite(byte addr, byte data) writes data in a given mode

byte CF_TaskFileRead(byte addr) reads data in a given mode

boolean CF_isBusy(void) checks the task file to see if the compact flash is busy doing something

boolean CF_isReady(void) checks if the CF is ready (apparently not the same as it not being busy)

void CF_ResetCard(void) resets the card by pulling the RST line high for 255 ms

void CF_Disable(void) sets the default CF unused configuration

byte CF_Enable(void) resets and enables the card for reading

void CF_Identify(void) sends the ATA Identify command and spits out (in big-endian) the 1kb of response. There is a lot of currently-unparsed data in there about the card but if you just look at the output you'll see some stuff that will reassure you that things are 'ok' For example, this is a Toshiba 128MB card:

mp3> i
Identifying CF.. „ŠB ÒSTCB21M8102YA07491A51.1 TOSHIBA THNCF128MAA ÒÒ

void CF_WriteByte(byte data) Strobes one byte of data on the data port

byte CF_ReadByte() Strobes one byte from the data port

CF_Write/Read16/32() does the above, but a few times in succession

void CF_StartSectorRead/Write() Readies the CF card to start reading from/writing to the sector specified in CF_CurrSector

void CF_Read/WriteSectorIntoBuff() reads/writes the contents of the sectorbuff array from/into the CF card.

void CF_DumpSector() dumps the sector specified in CF_CurrSector to stdout


This file contains the firmware for accessing the FAT16 filesystem on a compact flash card

boolean FAT_Init() fetches the MBR (sector 0x0 on the CF) and determines where the FAT and root directory are and formatting information such as sectors/cluster and the number of reserved sectors. It then initializes the player to the root directory

int16 FAT_findFreeClusters(void) goes through the FAT and counts the number of free clusters (which can then be translated into free bytes)

void FAT_ListDir(void) prints out file information for all the files in the current working directory (CWD)

void FAT_PrintCurrFileInfo() prints out the currently loaded file's info

boolean FAT_ChangeDir(char *dir) changes the CWD to be the subdirectory given (or the special un-subdirectories '..' & '.') It works, but I'm not using/supporting it.

boolean FAT_loadFileWithName (char *filename) loads the information for the given file named in the CWD

byte FAT_LoadFileInCWD(int16 filenumber) loads the information for the file which holds that slot number in the current directory, which is not necessarily the n'th file since there are slots taken up by deleted files, and long filename data.

boolean FAT_StartReadFileNum(int num) loads the file in slot number num and starts the microcontroller to read the first sector.

byte FAT_ReadNextSectorIntoBuff() reads the current sector of the currently loaded file and into the sector-size buffer, then it increments to the next sector.

byte FAT_ReadNextFileByte() returns the next byte of a file (as counted by File_CurrByte)

void FAT_ReadFile(char *name) dumps the named file to stdout

boolean FAT_CreateFile(char *name, int16 startcluster, int32 len) creates a new entry in the root directory for a file, then, starting with the given cluster, starts dumping data from stdin into the file until len bytes have been read. For best performance, give it precisely 512 bytes (or less) at a time, otherwise the uart buffer fills and it gets unhappy.

int16 FAT_findNextUnusedCluster(int16 oldcluster) returns the next unused cluster after the one specified. To find the first one, use 0x0002 as the first cluster.

void FAT_QuickFormat() wipes the FAT and root dir. You probably don't want to do this since it removes the 'bad sector' markings from the FAT.

void FAT_DeleteFile(char *name) Removes the given file from the root directory and clears all of its used clusters.

uint32 FAT_ConvertClusterToSector(uint16 cluster) Does the math to convert a cluster number into a sector number (there are multiple sectors per cluster, for FAT16 there can only be 2^16 clusters so if you want to address 2^18 sectors, there will be 4 sectors per cluster. This is all in the boot block in the MBR defined when you format the card.

uint16 FAT_GetNextCluster(uint16 cluster) Looks in the FAT to find the cluster that follows this one.


This file enables/configures/talks to the STA013 mp3 decoder chip, it also takes care of the actual playing of mp3's

void sta_enable/disable() pulls the enable line high/low

boolean sta_identify() requests to read the contents of register 0x1, which should be 0xAC if the STA013 is alive and kicking

byte sta_readreg(byte reg) returns the value in the STA's register reg

byte sta_writereg(byte reg, byte data) writes the data to the STA's register

byte sta_loadconfig() loads the data in config.c into the chip, necessary for it to function properly. Nobody seems to know whats in the file, but it might be a firmware upgrade that allows VBR/high bitrate playing. Also configures it for a 10MHz clock, see the STA013 datasheet/website for more info on what should be changed for different clocks

void sta_setvolume(byte v) sets the software volume, 0 is no attentuation, 255 is completely attenuated

byte sta_getvolume() gets the current software volume

byte sta_playfilenum(byte num) starts playing the file in the root directory in the nth directory slot.

byte sta_playfilename(char *name) same as above, but by name.


Contains the necessary firmware configuration data for the STA013, straight from STA's recommended datafile. The compiler didn't like it stored in one big block, so its in a few 1k pieces. Eit.


This file contains the code for I2C and SPI bit banging. the i2c code plays with the port C tristates, so if you change the pins around, make sure this is still valid.
The software program for communicating with the MintyMP3 player is written in java and tested on linux & w2k. God willing it will work on Solaris & MacOS. Right now it's talking plain serial so machines without serial ports (like Macs) will need a USB adaptor. Yeah, I'm planning on adding a USB port since everything has USB. Stop harrassing me! (V2 has a mini-b USB port and a serial to usb chip.)

Java Setup

You'll need to get the CommAPI from Sun. If you're running LinuxOS you'll also need the RXTX interface api for the CommAPI so that you can mess with the serial port.

So, first install whatever Java Runtime Environment you know and love, then the CommAPI, then you can run MintyComm.

How to "Use"

Start up the program by executing java MintyComm (or java -noverify MintyComm under Linux). Set the serial ports to whatever you have the mp3 player hooked up to, probably COM1 or COM2 and at a speed of 115kbps with 8 data bits, No parity, 1 Stop bit (8N1). There is a 4 second timeout before the player starts playing so hit Open Port and then turn on the mp3 player. You may want to see that the MP3 player serial port is working by plugging it in and using HyperTerminal to see if you get anything like:
Minty Mp3! v1 3/25/2004
Resetting Card..
# bytes/sectors: 512
# sectors/cluster: 4
# reserved sectors: 1
# FATs: 2
# / entries: 512
FAT starts at sector 0x0021
/ starts at sector 0x00000000020b
STA Reset
Found STA013
setting volume to -8 dB
waiting for char

Once connected it will display on the right the files on the compact flash card. You can then select local files on the left side and upload (>>>) them or delete files on the player. Note that uploading/downloading is really slow, on the order of 10KB/s. Eit. The microcontroller is the bottleneck, so it's not like USB would be any faster.

It's ugly, and it barely works, but it does work! I wouldn't interrupt a transfer in the middle, since it doesn't restart uploads (yet).


You can also connect to the mp3 player via serial port and a terminal program. Hit the keyboard when prompted to get to the mp3> menu. You can send it a bunch of commands to query/reset/enable/disable/initialize/test/etc. the hardware. See the firmware code mp3.c for the full menu.


The code is clobbered from the FileTree and SerialDemo code by Sun. It was written in 5 hours, I refuse to explain what I was thinking.
There are a few points to be made about making the player, so it's in your best interest to read this section if nothing else.

First, the PIC needs to be programmed with the bootloader. You can do this via in circuit serial programming (ICSP), but ICSP runs at 5V and the board should only run at 3.3V. For this reason, you should solder the PIC on, then program it, then continue with the remaining components. You can do your ICSP by soldering the three wires on the top right hand corner (MCLR/PGC/PGD) and another two to VCC and GND (as opposed to BATT+ which goes to the boost regulator). Once you are done you can disconnect the icsp wires.

One of the buttons' legs is in the way of the stereo jack so cut that off with a pair of snips.

Word! Version 2 is up and available. Rejoice!

This is an advanced project, I highly suggest that you don't take on a project like this to 'learn how to solder' or 'how to program a PIC'. If you can't handle fine-pitch SMT or getting boards made, just buy an MP3 player, they're sold in stores nowadays!

If you want to build an MP3 player, try something easier, like the Super Simple MP3 or you can even buy kits for the portable YAMPP-7 via JELU.

Get Parts

Buy or sample all the parts you need.
Make the PCB at a reputable PCB manufacturing house. Use a bandsaw or similar to get it into the right shape.


Solder the PIC18LF452 onto the board. Use something like solderpaste or high quality silver solder.
Tacked down mcu with solder paste

Swipe the soldering iron across the pins, or use a Black&Decker 'reflow' oven.

Solder a 3-pin SIP header in the top right corner, for programming through ICSP.

Make a dongle by soldering 5 wires (pwr, gnd, mclr, pgd, pgc) to a DIP socket.
Connect this to your programmer, plug the MCLR, PGD and PGC wires into the header, and use alligator clips or solder to connect power & ground.

Program in the bootloader (or the final firmware if you doubt you'll ever upgrade.) Verify that your bootloader is setup for 29.419MHz.

Solder in the power switch, and resolder the power line in the bottom left corner.

Solder in the two filter capacitors on the back (C31 & C39).
Solder on the microcontroller diode (D2), which is on the other side of the board for the current revision.

Solder the regulator (so, actually, I was having problems with it. So if you're going to be running from a lithium ion, and things are flakey, you can just short input and output on the chip) and the large filter cap (C8).

Solder on the 29.419MHz crystal (which might be in a different package) and the two capacitors (C11 & C12).

Connect the circuit up to 3.7V power, turn it on. Verify that the crystal is oscillating at the proper frequency.

USB (V2)

The USB subsystem allows us to load code to the microcontroller, and recharge the battery. Solder on the mini-B usb conncetor, the 6MHz crystal and two capacitors (so, actually, in the current version, this has been replaced by a ceramic oscillator that sits on the other side).

Solder the FTDI chip using the same technique used for the PIC micro. Solder on the passives necessary for the FTDI chip (these might have shifted around a bit: R21 thru R25, C32, C33, C35, C37, C42).
Plug in USB power, your computer should recognize it as a USB to serial converter. Drivers are available from FTDI if they don't come with your OS (most modern ones do).

Use the serial driver and tinybld16 (or, if you have decided on a different bootloader, the proper software) to upload the current MintyMp3 firmware. Turn Minty off and on, and use a terminal program (at 1152Kbps) to make sure Minty firmware is loaded. It should at least print out"Minty MP3! v2 3/25/2004" or something similar

Boost Supply (optional)

If you're going to run the player off of one or two 1.5V cells, now is a good time to put in the boost supply. Solder in the MAX756, C10, D1, C8, L1, C9 and run wires to JP3 (battery + and -). If you're not putting this part in, just solder in C8. If you want low battery notification (?) solder in LED1. (I've never actually used this so I don't guarantee its functionality. I'm pretty sure it works :)

Test the supply to verify it's giving you 3.3V out. Also make sure the PIC is still running at this point.

MP3 Decoder Chip

Solder in the STA013 chip, and the two filter caps nearby.

Solder in the passive components needed for the MP3 Chip.
<<<<More soldering here>>>


The completed PCB
What's in the box? Pain Minty!
~ Enjoy! ~


You can always get the BOM from the board by exporting it from Eagle. I HIGHLY suggest you look at the PCB thru Eagle to get a sense of where the components are as they change in minor revisions.

Also, if you want something easier, try Super Simple MP3 or you can even buy kits for the portable YAMPP-7 via JELU.


This is probably not packaged up correctly, if something is not working please post to the forums so it will be repaired
  • Version 1.1 (non-USB) PCB in EagleCad format (free PCB layout program)
  • Version 1.1 (matching above) Firmware in PICC format (with HEX and ASM) for 20MHz 18(L)F452
  • Version "1.1" (but really V0.000001) Java software for uploading over serial port at 115Kbps
  • The Tiny Bootloader I's quite nice...this is the HEX file I use for 20MHz and 19.2kbs communication. Its not necessary, but it is nice.

Enjoy more!

This is version 2, which is 'supported' and seems to work well, it includes USB. There are some pin changes so you can't mix firmware and pcb revs. I doubt I'll make any more changes other than bugfixes.
  • V2.3.1 PCB Files in Eagle 4.11 format (free software available for Win, Linux, and very soon MacOSX) with minor 'cosmetic' fixes that also includes a corrected BOM.
  • MIT-licensed (a derivative of the BSD license) V2 firmware & HEX file (now with subdirectory handling!)
  • The 29.491mhz tinybld bootloader HEX and asm file (for MPLAB assembler)
Is this for real?
Yes. Minty is a fully functioning mp3 player.
I have never soldered anything, should I try building a Minty?
You'll probably give up in frustration. This is an advanced project, for people with at least 1 year of smt soldering experience. There are other, much easier mp3 player projects out there. (See also q. #5)
Dude! This is cheaper than an iPod Shuffle! I'm totally going to build this!
Actually it's not, once you buy all the parts, with shipping and buy a CF card...chances are it'll run you $100 or more and that's -assuming- you own all the tools already!
Well that's stupid, why should I spend 5 hours building something when its cheaper to buy it?
Minty is an open source hardware project, partially to gauge whether it is possible to design and maintain such projects and whether people are interested in working on open source hardware. I do not expect people to try building it.
Will you sell kits?
Nope! This is a pre-Adafruit-kit project
How do I....?
Have you looked here or here?
Hey, there's a mistake...
Probably...the instructions aren't foolproof, and this is a very old project
I successfully built a Minty!
Really? Send us a picture & I'll put it up!

This guide was first published on Apr 21, 2013. It was last updated on Apr 21, 2013.