As Douglas Adams explained in The Hitchhiker’s Guide to the Galaxy, digital watches are “pretty neat” to us primitive life forms. Something about the marriage of practicality, and sheer nerdiness gets me oddly excited. Somewhere in my fascination I asked myself, “can I make a digital watch entirely of my design?” I did! And it taught me a lot about pcb fabrication, low power programming, and shift registers.
Probably the most important function of a watch is that it keeps time. While you could use your microcontroller to count the seconds and save on parts, there are some major downsides to this. For one, the microcontroller is much worse at keeping time than a dedicated RTC (Real Time Clock) IC, the time would drift significantly with temperature and battery voltage. Another serious problem is that it would require the microcontroller to always be on, keeping track of the time. This would consume much more current than an RTC IC, draining the battery significantly faster. Thus we employ a DS3231 to casually sit in the background, consuming microamps from it’s own back-up battery (which, at the rate of 200µA, would take 12.56 years to drain).
askoog89 saw a major flaw with many LED watches – you have to press a button to see the time:
I tried fix that problem by using a tilt switch to active the LED showing the time when tilt your arm to look at the watch
The watch uses the low power MSP430G2211 MCU from Texas instruments to control the LED and mesure the time with the help of a 32kHz watch cristal. The MCU sleeps most of the time only waking up ones a second to count up the time and check if the tilt switch is active. To show the time the watch uses 12 charlieplexed orange LEDs.
Callum Nunes-Vaz repurposed an old soviet vacuum fluorescent display (VFD) for use in a wristwatch:
The VFD display (IVL2-7/5) is a piece of soviet new-old-stock (NOS), and has a unique look to it. Making a watch out of it is a logical progression for anyone wants to give portability to the mesmerising glow of the display.
Callum shared the board on OSH Park:
Here’s a video of the display in action: