说明：  AVR ATtinyX5播放sd 卡 上的WAV文件。
(This is a simple SD audio player biult with only an 8-pin microcontroller. The ATtinyX5 series (25/45/85) 8-pin AVR microcontroller has two fast PWM outputs in 250kHz carrier frequency. This enables to output a wide frequency range audio signal. I built an audio player with the 8-pin AVR and an SD memory card (SDC). The SDC can be controled with only six lines, two for power supply and four for control signals. It can also be easily attached to 8-pin microcontrollers. The main application of the tiny X5 series AVR seems SMPS and related according to its integrated peripherals. Anyway this audio player is very simple and a few wires to be solderd so that it is suitable for brief soldering work before breakfast. There is an another project based on this project.)