The prototype uses a Wiseduino with DS1337 and a protoshield with 24 SMD LEDs.
Physically, on the board, the LEDs are placed in 2 "rings" of 12, the outside ring designated for minutes (red LEDs), the inside one for hours (green LEDs).
In the circuit, the LEDs are organized as a matrix of 5x5, as shown below.
The challenge is to display the time in an intuitive manner. For example, an analog clock moves its hour hand proportionally with the minutes. This is hard to achieve with relatively few stationary LEDs. Tricks need to be "invented" and even those may not be enough for an "accurate" display. Watch this video and let me know if what's shown is intelligible as a clock reading.
As seen in the video, the time is shown after the button is pressed. There are two reasons for that:
- since LEDs are the biggest consumers on this board, try to light them up only when necessary;
- for counting the flashing minutes there should be a start moment, and this is what the button provides.
Since this project will eventually evolve into a wrist-watch, a very important aspect is the power consumption.
Here are a few numbers so far (idle current/current with LEDs on):
To be practical as a watch, it will need a way to set up the time, which may require a second button (plus software, of course, to navigate the hours and the minutes).
Optionally, the watch may also have an alarm. This feature would require a small buzzer (plus, again, software to set up the alarm time and to activate the sound). The board size will be bigger and current consumption will be greater.
Somewhat similar projects on the interwebs (both featuring Microchip microcontrollers):