The peculiar feature of the "May 2015" revision of WiFiChron board is that it was designed to use software serial to communicate with either the XBee or ESP module. The reason is related to debugging. I wanted to be able to send messages to the serial monitor while (software serially) communicating with the serial device. This solution works well for XBee (GPSBee, BTBee), but not for ESP8266, only because the software takes more than the available 2K of RAM in this case (WiFi + software serial).
The immediate fix to use the ESP module is to connect its Rx/Tx lines to Rx/Tx of the processor. The existing connections can be left uncut, since they are not used in the sketch for ESP8266. The wiring should be like in the photo below.
The "permanent" fix would be re-designing the board to use ATmega1284 SMD (DIP-40 would not fit).
Talking about 1284, take a look at Farit's WiseClock4 mod. He used the WiseClock4 board, but completely re-wrote the software, including, it seems, the definition of new fonts. The SD card is now used for storing MIDI files (among others) that can play tunes through the Fluxamasynth shield.
A few of the other hardware and software features are:
- WiFi access to the internet through WiFly module;
- accurate time keeping through NTP;
- display weather forecast read from the web;
- daily alarms;
- automatic adjustment of the display brightness with light sensor;
- user-selectable display color.
And a photo of the internals, with the extra hardware:
Farit also shared the software he wrote, hopefully an inspiration for future mods.