1. Onboard mature and stable ESP-12F WIFI module, large capacity 4M BYTE FLASH 2. The I/O port of the WIFI module and the UART program 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 RST reset button. ESP-12F supports the use of development tools such as ECLIPSE/ARDUINO IDE, and provides for ARDUINO Reference program 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, RX, TX, and 5V of ESP8266 are respectively connected to the GND, TX, RX, 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 COM before it is closed, and it is suspended after being closed; COM: public end; NO: Normally open end, the relay is suspended before being closed, and shorted to COM after being closed. colour:Green Material:PCB size:87 x 93mm Package Contents: 2 x ESP8266 4 Channel Relay Module