Trying the Wemos D1 Mini ESP8266 module since it has a smaller real-state than the NodeMCU and enables us to build a PCB smaller than 5cm by 5cm. That's good, because some PCB manufacturers have special prices for PCB smaller than 5cm by 5cm.

I removed the external power supply. No more barrel jack, no more diode. This is both:

• to reduce costs
• to prevent connecting the D1 Mini with +9v since it only supports a max of +5.5v.

If you want to use an external power supply you can do it with this D1 Mini battery shield:

• http://www.wemos.cc/Products/battery_shield.html

Additionally I made the rounded corners. It looks nicer.