Get the PCB from https://oshpark.com/shared_projects/QrjTnDg1

Populate the PCB -- solder the ATmega328p, the reset resistor (10kΩ), the I2C pullup resistors (10kΩ, optional), capacitor (10-1000µF, optional). Solder the pin headers for the servos and power, and an extra pin or wire for the reset.

Connect your ISP programmer to the 3v3, GND, MISO, MOSI, SCK and Reset pins as follows:

If you are making the 2ch version, the pin names are printed on the PCB. Get the source code from https://bitbucket.org/thesheep/d1mini-18ch-servo/src for the 18-channel version or https://bitbucket.org/thesheep/d1-mini-20ch-servo/src for the 20-channel version. To flash the 18-channel version, use Arduino IDE. To flash the 20-channel version, run "make flash" in the firmware directory.

After flashing, set the fuses with:

avrdude -c usbasp -p m328p -U lfuse:w:0xE2:m -U hfuse:w:0xDF:m

Your shield is ready to be used!