The hardware design, as mentioned before, is based upon another MP3 player called Sakura, with few changes and different characteristics.

Anyways, the proposed design is very similar to the one found in the VS1011e datasheet.

The schematics diagram created for this MP3 player is the following:

VS1011e

This is the MP3 decoder chip. This chip has been selected due to its easy of use, good sound quality and mainly because it has a DAC built-in as well as a direct interface to the earphones, simplifying the design.

PIC18LF2550

This microcontroller was selected for many reasons. First of all, this is a low voltage version of the popular PIC18F2550 (that’s why the L in the chip’s name) and it’s very important because all the circuit logic works at 3.3V. Another reason took into account when selecting this chip was its high performance and speed (up to 20 Mhz) as well as the big program memory available for the firmware.
The PIC18LF2550 also has many modules that make it easier to implement certain firmware functionalities. Modules like SPI, USART, etc. It also features a USB module allowing the implementation of a USB interface with the computer in the future using this port.

SD/MMC

These types of memories are widely known and very popular due to its incorporation in cameras, cell phones and many other devices. They have a very low price comparing to the high capacity they provide and they use an SPI based protocol very easy to implement using microcontrollers. These memories work with 3.3V.

Voltage Regulator

The MP3 decoder chip, the microcontroller and the memory, they all need 3.3V to work. So, a voltage regulator has been selected to allow the circuit to work with just three 1.5V AAA batteries. The selected voltage regulator is provided by Microchip and the model number is TC1262, which is a high performance voltage regulator, specially created for low voltage devices using batteries.
Of course, there is more than one approach to supply 3.3V to the circuit, maybe using fewer batteries, like the use of the DC-DC step up converter MAX756 from Maxim that can supply 3.3V-5V using just one 1.5V battery or two.
In order to keep the circuit as simple as possible, the voltage regulator approach was used here along with some capacitors to filter the input signal.

Other components

Of course, many other components were used, like resistors, capacitors, LEDs, diodes, etc. The full parts list and their values are found below: