This module has a serial interface; therefore it only requires connecting 4 pins: Tx, Rx, 3V3 and Ground, as shown in this image from seeedstudio.
A few peculiar facts about ESP8266:
- default serial baud rate is 57600; since this rate is too high for SoftwareSerial library, a hardware port should be used;
- requires 3V3 for power and level shifting for Rx signal (5V to 3V3);
- physical interface is a 2x4 pin male header;
- firmware can be upgraded to a version that allows 9600 baud rate;
- can be used either as client or server.
It took me about half an hour to do it, following these steps.
- cut a piece of 2-mm perfboard to the XBee dimensions;
- solder two 10-pin the 2-mm-spaced male headers on the sides;
- desolder (using wick) the 2x4 header;
- mechanically attach the header-less ESP8266 module to the XBee perfbord, by soldering 4 pins into the corner holes, aligned with holes in the perfboard;
- wire the pins 1, 2, 3 and 10 of the Xbee-type module to pins Vcc, Tx, Rx and Gnd of the ESP8266 module respectively.
And now a few photos. Start with these (XBee shown for comparison purpose):
to make this:
Then plug it any Xbee socket, like one on Wise Clock 4:
or Adafruit XBee adapter:
Hopefully now more people can try adding new WiFi features to their Wise Clocks without breaking the bank (paying $35 for WiFly).