The Crowduino Uno-SD mainboard is a microcontroller board that completely compatible with the Arduino UNO. It is based on the Atmega328P, which is widely also used in the Arduino Uno and other Arduino compatible boards. Compared to the previous Crowduino with Atmega328, , the Uno SD mainboard uses the Atmega16U2, instead of the FTDI232 for the USB2UART conversation, which makes the program downloading much faster. Besides, there is a SD card slot on the Uno-SD board, making this board more convenient for applications such as data logging/ environment monitoring.     Compared to the original Arduino Uno, the Crowduino Uno SD board has the following upgrades:

• 1. Reset button on the left side, which makes it more convenient to reset the system.
   
• 2. Updated power circuit. With the selector, uses can select the working voltage, 3.3V or 5V, which makes the Uno-SD board compatible with more sensors that uses the 3.3V logic level communication .
   
• 3. Uno-SD board uses the Mini USB connector, to avoid the potential risk of connecting to above shield.
   
• 4. On board SD card slot.