Use a USB cable to connect the computer to the -USB interface on the board. After the driver is installed on the computer, you can see 4 COM ports appear. Use the short-circuit cap to select the desired VCC/TX/RX voltage on the TTL power selection interface to output corresponding voltage. The COM port with the smallest value corresponds to the first TTL interface, and with the largest value corresponds to the fourth TTL interface (the value of the COM port is not fixed). For a simple test, you can short-circuit TX/RX, and then use the host computer to send information to see if there is any data . VCC, TX,RX can all be switched to 5V/3.3/2.5V/1.8V The DC5.5-2.1 interface can provide high current to power external devices All four UARTs have TX/RX indicator to show the status The four serial ports use XH2.54 interface Colour:As Shown Material:PC+Metal Package Contents: 1 x USB to 4 Way TTL Module Only the above package content, other products are not included. Note: Light reflection 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.