For the definition of the SPI interface, see the silkscreen on the back of the adapter board. The 6 pin headers correspond to the SPI interface, from left to right: , , , MOSI, , Design background: The working voltage of the wireless module adapter board is generally 3.3v, while 51 single-chip microcomputer is 5v. This module is convenient for the use of our wireless module and the 51 single-chip microcomputer system board. VCC power supply voltage range of this module: 4.5-15V Application: used with NRF24L01 wireless module Material:PCBandPlasticandMetal colour:black Package Contents: 5 x adapter module Only the above package content, other products are not included. Note: Light and different displays may cause the color of the item in the picture a little different from the real thing. The measurement allowed error is 1-3cm.