Tic Tac Clock


Here’s an excuse to eat a bunch of Tic Tac candies: once the container is empty it makes a nice little enclosure for your next project. This particular offering introduces a point-to-point clock project that’s a ton of fun.

[Danny Chouinard] did a lot with very little. You can get the gist of the circuit just by looking at the photos above. it uses a 3×5 Charlieplexed LED display (this is given away by the fact that there’s only a few resistors on the board. A bit difficult to see, but between the resistors and the ATtiny84 there is a clock crystal, and on the back is a little piezo buzzer. The one thing that isn’t completely obvious is the power source. Two AAAA batteries, salvaged from a 9V battery, are able to keep the unit running at an estimated 2 years of moderate use.

The video after the break is worth a look though. It shows the various characters and information that can be flashed on the LED matrix. At first it’s hard to tell that the single user input button is being pressed by [Danny's] thumb.

If you don’t want to build a clock, there are still plenty of reasons to eat a whole container of these mints. You could replace them with a PIC programmer or a discreet camera.


  1. foolishdane says:

    The display is not charlieplexed, it’s multiplexed. So no, the few resistors is not equal charlieplexed.

    • Mike Rogers says:

      Charlieplexing would be considered a subset of multiplexing, right? (Charlieplexing = multiplexing + tri-state) So when in doubt, just say multiplexed and you’ll be right, then. So, the few resistors would suggest multiplexing.

  2. Mike Rogers says:

    I wonder if there’s enough room in there for a proper RTC. Perhaps not, I imagine that it’s a tight fit. A temperature compensating RTC would give the most accurate time, but I sure that adjusting for drift from the internal oscillator (as the write-up mentions) would go a long way. You might still more drift in summer vs winter, but I imagine that if a few precious seconds a month are going to mean life or death, you probably wouldn’t be using this to track the time anyway.

    Very thorough write-up, kudos.

  3. Rollyn01 says:

    Kind of reminds me of the old cheap wrist watches that just have two buttons to do everything. He just manage to add a lot more functions, reduce the button count to one, made it readable in reduced visibility situations (far-sighted, nighttime, etc.) and made it so that you can adjust the accuracy. Dude, kudos and then some. Would be nice to see this on the battlefield, though it would have to be waterproof. It could be a “We was here” key-chain.

  4. Rollyn01 says:

    Scratch that, just make it into a kit and I’ll be happy.

  5. Haku says:

    I’ve got a couple of empty Tic Tac boxes in my “might be useful one day” collection because they’re not the usual size, these ones are much larger than normal as they held almost three times the amount of sweets.

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