ESP8266 Sonoff Programmer

**First** and most important don't connect the mains power to the Sonoff module during programming. Personally I would not trust the PCB's electrical isolation and I value my PC's USB inputs, also we need to control the power to the ESP8266 to program it.
To put the ESP8266 into programming mode we need to hold the GPIO0 input low during a reset or power up cycle. On the Sonoff module neither the reset or GPIO0 is available on the optional headers. But the black push button is connected to the GPIO0 and pressing it takes this line low, so then all we need to do is cycle the power. That's how this box works.

Parts
USB serial cable - http://www.ebay.com/itm/Auto-Converter-Adapter-Module-USB-To-COM-Cable-USB-To-RS232-TTL-UART-PL2303HX-/182504686740?hash=item2a7e208494:g:yjcAAOSwXYtY2JFR

Normally closed push button - http://www.ebay.com/itm/Square-Momentary-On-Off-Normally-Closed-Push-To-Break-Switch-SPST-/252245252476?var=&hash=item3abafd197c:m:mDzggwvqL3y84SrcnNRIVLw

ASM1117 3