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The Sonoff Smart WiFi Switch is a very inexpensive (~$6 on Alibaba and ~$8 from US vendors (eBay or Amazon) WiFi controlled relay. It operates directly from AC power (110 or 220) and drives a 10A relay. There is a bi-color LED on board even though only the green LED is used in the WiFi application. It looks like the PWB can also accommodate a 433MHz receiver and be operated from a battery operated remote controller and the red LED is used in that application. The schematic is available from Itead, the manufacturer of the device Sonoff Basic Schematic