A weblog focused on interesting circuits, ideas, schematics and other information about microelectronics and microcontrollers.
Motion controlled MP3 player
The MP3 player does not have any buttons nor dials that shown in right photo and it has an acceleration sensor instead of the mechanical switches. Therefore all playback commands to the player are given in defined motions, such as inclination, tilt and shock. The player detects the motion with the built-in acceleration sensor and recognize it as a playback control command. As the result, it came to not seem an audio player in appearance.
An Atmel AVR microcontroller that my favourite MCU family is used for embedded controller. The controller chip chosen for this project is ATmega644. The operating clock source is internal 8 MHz oscillator.
A KXM52-1050(Kionix) ultra small (5mm sq.) 3-axis acceleration sensor is used. The working acceleration range is ±2G but it is too high sensitivity for this purpose. Especially the working range for direction of lower (it is most significant) becomes only 1G due to an offset by gravity. If output voltage is saturated, the acceleration cannot be integrated with accurate so that any consideration may be required to the motion analyzing process. ±5G will be proper for this use when any other one is selectable.
SD Memory Card is the de facto standard in flash memory card. It can be attached to the microcontroller via a few signal lines. FAT format is used to store data files in it so that the project using the memory card must implement the FAT file system. Fortunately, there are various FAT libraries on the web as freeware so that everybody can use the memory card in their project with ease.
Because the MP3 player is a portable equipment, it has two RCR123A(3.6V, 650mAh) Li-Ion cells in parallel for power supply. The playback time became approx. 20 hours when fully charged but it depends on the volume.
To decode MP3 audio data stream into PCM data, I used a VS1011e(VLSI Solutions) which integrates a DSP, a D-A converter and a headphone amplifier on a chip. It can be obtained easy and can achieve decent audio performance. It is often used as many as ST's STA013 for home-built MP3 projects. The drive capability of built-in headphone amplifier is insufficient to drive loudspeakers so that I put an external power amplifier after the decoder chip.
The MP3 player is built into an existing PC speaker.