Binary wrist watch guarantees being identified as a nerd

I have just finished my binary wrist watch project (well, the new revision anyway). I was surprised at how small I was able to make it compared to last time.

I chose to go with the “super-yellow” color LEDs as they fit the purple OSHpark PCB very nicely. The biggest challenge was actually making a good looking wrist band for the watch. I originally intended to use a design like this but it turned out that due to lack of enough para cord I had left, I went with a simpler design that I had done once before.

The watch in it's natural environment. The time displayed is 18:23 (6:23 PM)
The watch in it’s natural environment. The time displayed is 18:23 (6:23 PM)

Unfortunately I used the wrong footprint for the PIC when laying out the PCB. The PIC comes in a SSOP-20 package and the footprint marked “SSOP-20″ in the KiCAD library is actually a TSSOP-20. Ridiculously enough there’s also a separate TSSOP-20 footprint in KiCAD.
I was able to get away with bending the pins of the SSOP inward and then reflow soldering it to the TSSOP footprint. It’s a bit of butchery but I couldn’t give this one to Mr. Murphy.

Sorry, Mr. Murphy!
Sorry, Mr. Murphy!

After getting all the hardware wrapped up, I could start coding. The watch can be woken up from sleep mode (display off, only RTC running) by holding the right button for one second. It can be put back into sleep mode by holding the right button for one second again.

In sleep mode the watch consumes about 150µW when powered from a CR2032.
I don’t know how accurate my meter is at the µA range, I might measure the consumption again after receiving one of Dave Jones’ µCurrent measurement adapters.

Somewhere in the PIC datasheet it is mentioned that floating pins should be pulled to VDD or GND when not used to prevent excess power consumption because of switching currents. I haven’t done this in this revision of the board and I don’t know how big the impact on power consumption would be.

The time setting mode can be entered by holding the left button for two seconds. After that the display is blanked and the time can be set bit by bit by switching through the bits by pressing the left button. If the bit is to be set, the right button has to be held down for one second. The watch automatically enters normal display mode after the last bit has been set (once you’ve gone through all the bits).

All there is left to do is see how well it will hold up when I wear it every day and how long the battery will last.

Altough not having worn the watch in the presence of normal humans, I can already guarantee that now everyone will be able to easily identify me as a nerd.

5 thoughts on “Binary wrist watch guarantees being identified as a nerd

  1. Hi,

    How can i get this product?
    Can you just tell what are all the components u used to build this. I am interested to have a similar product for myself.


  2. Pretty cool project. Will be looking for updates on battery life, nerd cred received, etc. ;’)

    One thing I’d do, knowing how hard I am on watches, is build a little form around the top and pour in clear epoxy, leaving only the button tops exposed. That would make it nearly bullet proof and possibly add to the cool factor.

    Also, one question. How is the display arranged? Am I right in reading the time as 22:27 ?

  3. I’d say the time is 11:27hrs, only two bits for hours and four bits for minuts. This watch is great, some division would be great, lets say an extra blinking led for seconds between hours and minuts

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