Changes

*1Remove the hardware ASD function and change it to software implementation* PIN33 (GPIO13) is replaced by the PIN37 (GPIO26) to avoid the I2S interface from v1.3 to v2.0. * Improve the power path function, the battery will only charge and not discharge when connected to the PSU(power supply unit). [The PSU power will charge the battery and also pass through to the RPi when it has power. If the PSU loses power (power failure), the X728 will switch over to battery power.]*2. You can choose to charge when boot up by short "CHG EN" and stop charging at shutdown.*3. Use ultra-low voltage MCU. *4. Increase battery overcharge, overdischarge protection circuit, added power input surge protection circuit.*5. Added power input connector, which can be used with X715 to achieve 6~60V wide voltage input.*6. PCB Size change: 87x63.7mm