A Simple Binary Coded Decimal Watch

Analog and LCD watches are both useful designs, but ultimately are mainstream timepieces. Using a binary watch is an easy way to set one’s self apart as a tech enthusiast, while impressing your hacker friends to boot.

One such build comes to us from [vishalsoniindia], and it uses a single bare PCB which is designed to mate directly to a traditional watch strap. The single tactile button on board is used to activate the watch, showing the current time in hours and minutes in binary-coded decimal on the watch’s LEDs. Long-pressing the button puts the watch in setting mode to correct the time as needed.

The watch relies on an ATtiny85 microcontroller, a lightweight and compact design which is more than powerful enough to run a simple watch. It’s paired with a 74HC595 shift register to run all the LEDs from a minimum number of pins, and there’s also a TP4056 charging circuit on board to keep the lithium-polymer battery topped off.

A project like this is a great way to learn all manner of basic electronics skills, from PCB design, to SMD soldering and even working with basic logic parts like shift registers. As a bonus, you get a cool watch out of it to boot.

We’ve seen some similar designs over the years, as varied as the hackers that build them. Video after the break.

13 thoughts on “A Simple Binary Coded Decimal Watch

    1. mainstream most likely not. the binary watch is a niche market product for consideration of mass production.yo You have to take consideration of ROI from investment in production. the more you bulk purchase and have more units on standby for production the lower the cost of manufatcuring the product and the greater the return, as long as you can sell that many units of the product. best to make your own or if you really want to buy one there is a company that made one. google this phrase “the one binary watch” i actually purchase one when they first hit the market. it’s a nice little watch . still use have it to this day.

      tldr google the phrase “the one binary watch”

  1. QQ: How does the micro keep time accurately?
    IIRC, an Real Time Counter is not accurate enough, as well as a normal timer?
    Next revision will probably include a smaller shift register, and there will probably be space for a TXCO RTC (Real Time Clock), such as a DS3231.

    Aside from the short-comings, good looking watch.
    Reminds me of the bulky looking nixie watch, that even the Woz wore at a time…

        1. Yes, and it’s the biggest component on the board, which is why I suggest you might actually be able to get rid of it with some more clever coding and board routing.

          1. This is what I don’t get as well. He used an ATTiny85, just to use another IC for driving LED’s anyway. There’s a few more ATTiny’s with more IO that would omit the need for a shift register at all.

          2. Looks like 8 LEDs so that’d be what, 4 IO afaik to drive (well could do up to 12 LEDs). I think the attiny85 can have up to 6 gpio if you enable the reset pin as io so there’d be plenty to charlieplex.

  2. i made a 24-bit binary counter tuned to roll over once a day as a clock…i wondered if i would ever find it useful, since there’s no obvious way to convert its output to the hours and minutes that we schedule our days by. i mean, you can just look at the first bit to tell AM/PM but beyond that it gets a lot rougher. BCD solves that problem nicely, though obviously it’s now a totally different kind of beast.

    but it turned out i never found it useful for a different reason…i used a 555 so it keeps crap time. drift out the wazzoo

  3. Technically, it isn’t a BCD (Binary Coded Decimal) watch.

    The minutes on this watch are displayed in pure binary, e.g., 32, 16, 8, 4, 2, 1, while if BCD, it would be 4, 2, 1 (tens digit), then 8,4,2,1 for the ones digit. So, the watch as shown would display 36 minutes as 100100, while if it was in BCD, it would display 0110110. It would also require and extra LED for the minutes in order to represent 00 through 59 in BCD.

    It’s a nit, for sure, but being a student of vintage electronic calculator design, BCD is the most common representation used in calculators, so it was immediately obvious to me that the BCD nomenclature used in the article was technically incorrect.

    All that aside, this watch a really nice build, and is a device that would certainly draw curious attention from the “public” when worn.

    Speaking of LED watches, I get all kinds of questions when I wear my vintage 1977 Hewlett Packard HP-01 (https://oldcalculatormuseum.com/hp-01.html) LED calculator/watch out in public (which I don’t do very often). It never fails to bring people’s curiosity to the fore when they notice the tiny keyboard. They are really startled when I flip my arm over and pull the small stylus built into the watch band clip to operate the device, and they see how amazing the HP-01 was for its time. It was the “Smart Watch” of the late ’70’s.

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