Plans for the Next MP3 Player

Description: This new design has replaced the old one. The design shown on this page is obsolete. The new design has more features, is flash upgradable, is much easier to use, costs less, and is actually available for purchase. It is superior to the old design in almost every aspect. The old pages remain accessible, primarily for reference. This design data is distributed with the expectation that it will be beneficial, but it comes without any warranty, including implied warranties of merchantability or fitness for a particular purpose. Matthew Burnham reported successfully building the circuits shown in this schematic. The diagram was created after constructing the player, and it appears to be accurate. It is advisable to avoid inserting the MAS3507D chip into its socket until the 3-volt power supply has been verified, as the decoder chip is expensive and may be damaged if 5 volts is applied. For those concerned about sound quality, additional power supply bypassing may be beneficial for the D/A converter, potentially using ferrite beads or inductors. The CS4327 chip should be utilized with a low-pass filter on its outputs; this was not included in the initial board design but will be added in future iterations. The CS4327 data sheet contains useful recommendations for implementing a low-pass filter. The pushbuttons are straightforward, with the 8051's port pins providing the pull-up resistors, requiring only the connection of three normally open momentary contact buttons. The firmware includes code to debounce the signals. This last circuit is optional; if it is not implemented, the signal that would typically drive the 8051's RXD pin must not be connected. When the firmware operates the 8051's serial port in mode 0, both TXD and RXD become output signals. A tri-state buffer is used to disconnect the standard receive signal from the RS-232 interface, preventing logic conflicts between the 8051 and the standard receive signal. Snail Instruments, a small company in the Czech Republic, offers the MAS3507D and DAC3550A chips for $35. The previously convenient PLCC package is no longer available, but a small adaptor board is provided. An alternative option is to switch to the STA013 chip, which accepts data in the same format as the MAS3507D but requires initialization via I²C.

The updated design integrates several enhancements over its predecessor, focusing on user-friendliness and cost-effectiveness while maintaining high-quality performance. Central to this design is the MAS3507D, a digital audio decoder that necessitates careful handling during installation due to its sensitivity to voltage levels. The design emphasizes the importance of verifying the power supply voltage before inserting the MAS3507D to prevent damage.

Incorporating the CS4327 D/A converter requires the addition of a low-pass filter, which is crucial for minimizing high-frequency noise in the audio output. The design can benefit from various filter configurations as suggested in the CS4327 data sheet, which may include passive RC filters or active filter circuits.

The user interface is simplified through the use of momentary pushbuttons, with the 8051 microcontroller managing the input signals. This approach leverages the internal pull-up resistors of the microcontroller, reducing component count and complexity. The firmware is designed to handle signal debouncing, ensuring reliable button presses are registered without false triggers.

The serial communication aspect of the design is handled by configuring the 8051's serial port appropriately. The inclusion of a tri-state buffer is a strategic choice to avoid conflicts during data transmission, ensuring that the RXD pin does not interfere with the normal operation of the system when in use.

Finally, sourcing components from Snail Instruments provides a reliable option for acquiring the necessary chips, while the consideration of alternative components like the STA013 chip allows for flexibility in design and implementation. This comprehensive approach to the design and component selection ensures a robust and efficient audio playback system.This new design has replaced the old one. The design shown on this page is obsolete. The new design has more features, is flash upgradable, is much easier to use, costs less, and is actually available if you`d like to buy one! It`s better than this old design is almost every way. These old pages are still available, mostly for reference. Disclaim er: This design data is distributed in the hope that it will be useful, but without any warranty; without even the implied warranty of merchantability or fitness for a particular purpose. Matthew Burnham reported that hy built the circuits shown in this schematic and got it to work. This diagram was drawn after I built the player, bit it looks like it`s probably correct. It`s a good idea to avoid placing the MAS3507D chip in its socket until the 3 volt power supply has been verified.

The decoder chip is expensive and it probably will be damaged if 5 volts is applied. If you are very concerned about sound quality, you may want to add more power supply bypassing to the D/A converter, perhaps with ferrite beads or inductors. The CS4327 chip is supposed to be used with a low-pass filter on its outputs. I didn`t build this on my first board, but I will add it to my next design. The CS4327 data sheet has some good suggestions about what to do for a low-pass filter. The pushbuttons are very simple, and the 8051`s port pins provide the pullup resistors, so all that is necessary is to connect the three buttons.

They must be normally open momentary contact types. The firmware contains some code to avoid de-bounce the signals. This last circuit is optional, but if it is not used, whatever signal would normally drive the 8051`s RXD pin must not be connected. When the firmware uses the 8051`s serial port in mode 0, both TXD and RXD become output signals. This tri-state buffer just disconnects the normal receive signal from the RS-232 interface, so that there won`t be a logic conflict between the 8051 and the normal receive signal.

Snail Instruments, a small company in the Czech Republic, is offering the MAS3507D and DAC3550A chips for $35(us). It seems the eady-to-use PLCC package is no longer available, but they have an small adaptor board. The other alternative is to attempt to change to the STA013 chip, which accepts data in the same format as the MAS3507D, but also requires initialization with I ²C.