When I started layouting the PCB for my irrigation sensor I realized the advantages of a breakout board. They are handy for developing, sure. But they also bear the big advantage that you do not have to take care about repetitive tasks (such as pull-up resistors). Additionally they ease up layouting by adding two additional layers to your design. That simplifies the design and it also minimizes the footprint of the final PCB.
Size was the most important factor for me. It isn’t just a question of space, it is also a question of price (PCB cost ist based on cm²). Beside the pull up resistors for CH_PD, GPIO_0, GPIO_2 and RESET and the buttons to ground RESET and GPIO_0 (PROG) I have also foreseen a pin header for connecting my XCSOURCE FT232RL USB<->TTL. The voltage supply of the USB-TTL converter can be enabled or disabled with a jumper. Additionally I have foreseen solder jumpers CTS->REST and DTR->GPIO_0. I’ve not tried personally but some sources say that this connections make the manual buttons obsolete by handing over this task to the USB-TTL converter. Finally there is also a solder jumper to connect GPIO_16 and RESET (for wake up after deep sleep) and a capacitor as voltage stabilizer. Other boards like the Huzzah Board use a voltage converter for this but I have made good experience with the capacitor.
My followers on twitter know that it took several attempts before I got my final version ready (special thanks here to @ccxx72, @i_grr, @bdcatalin und @tzapulica for their help). I also faced some troubles with Fritzing but finally you can download my result at Github: https://github.com/Stromspielplatz/misc/tree/master/ESP8266%20ESP-12%20Breakout
