Hacking DWex into combo analog-digital clock

DWex, my forgotten watch, was not a successful project, probably because I rushed its design, I spent more money on it than I planned and I did not follow up with revisions. DWex was also not offered as a kit, but as an assembled board with SMD components, not easily hackable or expandable, pretty much a dead end from hardware perspective. Its idea is still sound though, after so many years: mostly sleep, to conserve battery, then, at a press of a button, flicker some LEDs to indicate the time.

This rainy Easter weekend I stumbled upon the few DWex boards I still have, and they brought back memories. One thought lead to another, and I found myself, characteristically (I am the "penny wise, pound foolish"- kind), soldering around once again. So here I am, writing another useless post, about another useless project, on how to convert time, money and energy into joy, sometimes mixed with frustration, when things don't work on the first try (as it's usually the case).

DWex is equivalent to a smaller wsduino (ATmega328 + RTC), with 24 LEDs. Why not recycle it into something physically "bigger", by adding extras (alphanumeric display, micro switches, ESP8266, OLED etc.)?
The design of the DWex board has a few peculiarities:

• RTC chip is DS1337, with support for alarms;
• the on-board CR2025 3V battery powers the whole watch, not only the RTC (there is no time keeping without a battery);
• FTDI connector does not have Vcc wired, relying instead on the battery to power the processor while uploading the sketch;
• the ATmega328 processor is clocked with an external 8MHz crystal, thus making the board compatible with LilyPad 328;
• pins available are D11, D12 and D13, all broken out on the ISP connector (unused are also D2 and D10, but they would need to be wired directly from the processor's pins);
• features only one button.

But the most particular aspect of DWex is the way it shows the time on the analog round face, by blinking LEDs on request (button push). This is actually not suitable for continuous display, simply because it is confusing to make sense of non-stop blinking LEDs.
OK, so enough complaining. Here is what we plan to do:

• add a 4-digit alphanumeric Adafruit I2C 0.54" display;
• add ESP8266 module to sync the clock on NTP;
• add toggle switch for setting up wifi parameters (for ESP8266);
• use RTC's alarm capability; add toggle switch and buzzer (or other audio module) for alarm mode;
• add OLED (I2C) for displaying messages, info etc;
• modify the software, a combination of DWex and WiFiChron, to support all of the above features, plus change the way the time is shown on the analog face (no more sleep, no button press to show the time);
• add "seconds" mode, on the digital display;
• maybe adapt the 8-character-based menu system from WiFiChron to 4-character (by showing only the first 1 or 2 letters of the menu);
• add 3V3/500mA regulator to the board.

This will be a work-in-progress for a while, especially on the software (which I will publish later).

WiFiChron support for 16-segment LED display

This is the second time I am writing this post. First time it just disappeared after almost 2 hours of editing. I started the post by saying that whenever I want to have some electronics fun, I open one of my drawers. Nice story line, but I am too frustrated now to recreate it from memory. (The lesson I learned is that I should write it first as a document, save locally, then copy and paste into a blog post.)
So I will keep it short and dry.

Some time ago, I designed this "4-character 16-segment 1-inch LED" board (pictured below), briefly mentioned here. I abandoned it, after a couple of failed tries, while writing the character definitions. Since then, I discovered the Adafruit 4-char alphanumeric LED backpack, which comes with nice software support as well.

For WiFiChron, two cascaded modules make an 8-character display functionally similar to HDSP-2534, but bigger and more visible. With the "Display Abstraction Layer" already in place, software support should be easy to integrate, since controlling it with the HT16K33 breakout allows the re-use of the above mentioned Adafruit LED backpack library. For maximum compatibility, I followed the same wiring, then connected the two extra segments, A2 and D2, to pin 10 (not connected for the 14-segment backpack) and pin 11 (connected to the DP), respectively.

I added a new class, Alphanum8x16, to the original files (Adafruit_LEDBackpack.h and cpp) to control the extra segments:

class Alphanum8x16 : public Adafruit_AlphaNum4
{
 public:
  void writeDigitAscii(uint8_t n, uint8_t ascii);
};

void Alphanum8x16::writeDigitAscii(uint8_t n, uint8_t a)
{
  uint16_t font = pgm_read_word(alphafonttable+a);
  displaybuffer[n] = font;

  //--------------------------------------------------------
  // this is the Adafruit mapping of digits to segments:
  // 0 DP N M L K J H G2 G1 F E D C B A
  //
  // this is the 16 seg mapping of digits to segments:
  // A2 D2 N M L K J H G2 G1 F E D1 C B A1
  //
  // bits:
  // 1  1  1 ...                 ...  1 0
  // 5  4  3
  //
  // Note: DP is not connected/controlled for the 16 seg;
  //--------------------------------------------------------

  // if A1 (bit 0) is on, set A2 (bit 15) as well;
  if (font & 1)
    displaybuffer[n] |= 0x8000;

  // if D1 (bit 3) is on, set D2 (bit 14) as well;
  if (font & 8)
    displaybuffer[n] |= 0x4000;
}

The 8x16-segment display is implemented in class DisplayHT16K33 in the WiFiChron software.
So far, WiFiChron can support the following displays (defines in DAL.h):

//#define DISPLAY_HDSP2534
//#define DISPLAY_DL1414
#define DISPLAY_HT16K33
//#define DISPLAY_OLED
//#define DISPLAY_HT1632
//#define DISPLAY_MAX6955

In principle, any display that can show 8 characters can be used through DAL.