1. On-board mature and stable ESP-12F wifi module, large-capacity 4m bytes flash memory; 2. The I/O port of the WIFI module and the UART program download port are all led out to facilitate secondary development; 3. The power supply mode supports AC90-250V/DC7-30V/5V; 4. The first reset button of the wifi module on the board; 5. ESP-12F supports the use of development tools such as eclipse / for arduino ide, and provides reference programs in the for Arduino development environment; There are 4 5v relays on the board, which are used to switch output signals and are suitable for controlling loads whose working voltage is in the AC range. On-board power indicator, 1 programmable LED and relay. Power supply: 4 channels: AC90-250V/DC7-30V/5V Writing mouth: The GND, RX, TX, and 5V of ESP8266 are connected to the GND, TX, RX, and 5V of the external TTL serial port module respectively. The IO0 should be connected to the GND when the download is complete. Disconnect the IO0 and GND after the download is complete. Relay output: NC: normally closed end, short connect with COM before relay closing, suspended after closing; COM: public terminal; NO: normal start, the relay is suspended before closing, and short connected with COM after closing. Colour:green+blue Material:PCB+electronic components Size: 93 x 87mm Package Contents: 2 x ESP8266 Wireless WIFI Relay Module