When I started going down the path of automating my lighting, I came across the Itead Sonoff Wi-Fi Smart Switch, a very inexpensive mains switch operated by an ESP8266. The supplied app was one of those "call out to a server on the internet to turn on your lights" ones I had no interest in, but a blogger, Peter Scargill, showed how easy it was to re-flash the firmware because the serial pins are broken out to pin holes on the PCB. I whipped up some firmware that would respond to serial commands to turn off and on the mains switch (Wi-Fi is not even active in this incarnation of the ESP8266 firmware). An NRF51822 module is then connected to the serial and power pins of the Sonoff Switch. The NRF51822 is flashed with a slightly modified BLE_Gateway example from the nRF OpenMesh repository, which sends those serial commands to the ESP8266 in response to a value change in the mesh.

On the other side, another NRF51822 modules is flashed with modifications to the BLE_Gateway, which change that mesh value in response to a switch. The result can be seen below.

After proving out this functionality, the rest of this project is basically software. A lot of software.

The inclusion of the ESP8266 based Sonoff gives the possibility of a bridge between the Bluetooth Mesh, and IP based services. While this bridge opens up another attack surface that must be secured and adds a configuration headache, it gives the possibility of added functionality. Through this bridge you could be alerted if your lights are going on and off while you are out of town on vacation.