Features Better Control --- One on board MCU controls LED, and the IO port can connect to P3.2 for output, such as PWM wave modulation experiment. One Way Switch --- One channel switch chip on board, connect to IO port P3.3, which can be used for input, interrupt and other experiments. Stable Working --- The switches and LEDs of the external chips of the IO port do not affect the normal use of the IO port. 4 Sets in All --- There are 4 sets of MCU development board, and the large quantity will meet your needs for replacement. All IO Port Out --- All IO ports are led out, so the light weight and compact microcontroller system board is easy to install. Specification: Item Type: Microcontroller System Board Material: PCB Board Size: Approx. 12 x 18mm / 0.47 x 0.71in Package List:4 x Microcontroller System Board 4 x Pin Header Package List 4 x Microcontroller System Board 4 x Pin Header