1. Onboard mature and stable ESP-12F WIFI module, capacity 4M FLASH 2. The I/O port of the WIFI module and the UART download port are all led out to facilitate secondary development 3. Onboard AC-DC switching power supply module, power supply mode supports AC90-250V/DC7-30V/5v 4. Onboard WIFI module reset button. ESP-12F supports the use of development tools such as / IDE, and provides for Reference in the development environment 5. Onboard 4 5V relays, output switch signal, suitable for controlling the working voltage of AC Load within 250V/DC 30V. On-board power indicator, 1 programmable LED and relay indicator. Burning port: The GND, , TX, and 5V of ESP8266 are respectively connected to the GND, TX, , of the external TTL serial port module 5V, IO0 needs to be connected to GND when downloading, and then disconnect the connection between IO0 and GND after downloading; Relay output: NC: Normally closed, the relay is short-connected with it is closed, and it is suspended after being closed; : public end; NO: Normally open end, the relay is suspended being closed, and shorted to after being closed. colour:Green Material:PCB size:87 x 93mm Package Contents: 1 x ESP8266 4 Channel Relay Module Only the above package content, other are not included. Note: Light and different displays may cause the color of the item in the a little different from the real thing. The measurement allowed error is +/- 1-3cm.