A Solar-Powered Wristwatch With An ATtiny13

March 13, 2024 by Maya Posch 22 Comments

Wristwatches come in many shapes, sizes, and types, but most still have at least one thing in common: they feature a battery that needs to be swapped or recharged somewhere been every other day and every few years. A rare few integrate a solar panel that keeps the internal battery at least somewhat topped up, as environmental light permits.

This “Perpetual” wristwatch designed by [Serhii Trush] aims to keep digitally ticking along using nothing but the integrated photodiodes, a rechargeable LIR2430 cell, and a power-sipping face that uses one LED for each hour of the day.

The face of the perpetual wristwatch. (Credit: Serhii Trush)

The wristwatch’s operation is demonstrated in the linked video (in Ukrainian, auto-generated subtitles available): to read out the current time, the button in the center is pressed, which first shows the hour, then the minutes (in 5 minute intervals).

After this the ATtiny13 MCU goes back to sleep, briefly waking up every 0.5 seconds to update the time, which explains why there’s no RTC crystal. The 12 BPW34S photodiodes are enough to provide 2 mA at 0.5 V in full sunlight, which together keep the LIR2430 cell charged via a Zener diode.

As far as minimalistic yet practical designs go, this one is pretty hard to beat. If you wish to make your own, all of the design files and firmware are provided on the GitHub page.

Although we certainly do like the exposed components, it would be interesting to see this technique paired with the PCB watch face we covered recently.

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A vintage watch with a new PCB inside, next to a 3D rendered image of the PCB

Modern, Frugal PCB Breathes New Life Into Soviet-Made LED Watch

March 31, 2022 by Robin Kearey 12 Comments

The first electronic digital watches were admired for their pioneering technology, if not their everyday practicality, when they were introduced in the 1970s. Their power-hungry LED displays lit up only when you pressed a button, and even then the numbers shown were tiny. Their cases were large and heavy, and they drained their batteries rather quickly even when not displaying the time. Still, the deep red glow of their displays gave them a certain aesthetic that’s hard to replicate with today’s technology.

A vintage LED watch displaying "16.42" — Pressing the top-right button enables those beautiful LED modules

When [Benjamin Sølberg] got his hands on an Elektronika-1, a first-generation digital watch designed in the Soviet Union, he set about designing a modern replacement for its internals. Where the original had several custom chips wire-bonded directly onto a substrate, the new board contains an MSP430 series microcontroller as well as an AS1115 display driver. The PCB makes contact with the watch’s pushbuttons through clever use of castellated holes.

For the display [Benjamin] went with period-correct LED modules made by HP, which keep the display’s appearance as close to the original as possible. While these draw quite a bit of current, the rest of the watch has become an order of magnitude more frugal: the stand-by time is now estimated to be about ten years, where the old design often needed new batteries within a year. [Benjamin] uses his renovated watch on a daily basis, apparently without trouble.

If you’ve got an old Soviet digital watch that you’d like to upgrade, you’ll be pleased to hear that the entire design is open source. Just like this retro watch, in fact, that uses a similar LED display. If you’re into original vintage watches, we’ve covered them in depth, too.

A BCD Wristwatch You’d Want To Wear

July 24, 2018 by Jenny List 4 Comments

Timepieces are a staple of Hackaday, we have featured so many of them over the years that for us to become really excited by a fresh one it must be particularly special. The days when simply breaking out the Nixies was enough are long past.

So this binary wristwatch project by [Sverd Industries] definitely caught our eye. Not for being particularly novel, after all binary LED clocks are not in themselves hard, but for the exceptionally high quality of its construction. It’s a simple enough design, with a real-time clock chip and an ATmega328 in its most power-sipping mode on a circular PCB with an array of LEDs as the display, and all contained within a 3D-printed shell.

This design has real quality, the discrete components are tucked underneath the board leaving the ICs on the top with only the LEDs for company. The glass front is glued into place, and the shell is professionally 3D-printed. Power comes from a single CR2032, and to save battery life the LEDs are only activated by the press of a concealed button. We would wear this watch. For that matter, you would wear this watch. Take a look at the video below the break, and we’re sure you’ll agree. Looks like a few are even available over on Tindie.

This isn’t the first binary watch we’ve featured, so it’s tough to pick a comparison. This very low BoM example might lack some of the polish of the one presented here, but it has the same ability to catch our eye.

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