color: blue Material: PCB Product Name: Relay Module LED D6 (green): working status indicator, the details are as follows: (1) When the unit is off, the router is being configured or disconnected from the router. (2) 0.5s flashing quickly indicates that the mobile phone application is configuring the WIFI account and password for the ESP-01 module. (3) 2S slow flashing completes the configuration and waits to establish a connection with the mobile phone via TCP (4) The LED is always on, indicating that the TCP connection with the mobile phone is successful. The reserved two cap jumper connections: Usually, they are inserted into the bottom, ie RX to RX1, TX to TX1. When using them as USB modules, insert them into the upper COM1 COM2 COM3 COM4: Common terminal NC1 NC2 NC3 NC4: Normally closed NO1 NO2 NO3 NO4: Normally open Relay control (hexadecimal format): Disconnect relay 1: A0 01 01 A2 Closed relay 1: A0 01 00 A1 Open relay 2: A0 02 01 A3 Closed relay 2: A0 02 00 A2 Disconnect relay 3: A0 03 01 A4 Closed relay 3: A0 03 00 A3 Disconnect relay 4: A0 04 01 A5 Closed relay 4: A0 04 00 A4 Board size: 59 * 40mm Package Contents: 1 x DC12V ESP8266 four-channel Wifi relay 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.