It all started with the idea of a PCB which could display the time in BCD code....

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The original Idea was to create a Wrist Watch which shows the Time in BCD Code and 24h Format. Since i could not find a affordable and good looking Watch which matched all the criterias the obvious solution was to start building one.
After the first prototype PCB was working i couldn't find a Housing which could be easily repurposed, so i started to design a Housing in OpenSCAD.
After i started to wear the first watch for daily use the project started to escalate.
At first there was an additional Version which displays the Time in an analogish way.
When the first Problems occured with sweat entering the Device i experimented with various ways to waterproof the PCB.
The next step was to introduce a G-Force Sensor and remove the Buttons.

It all started with the idea of a PCB which could display the time in BCD code and is small enough to wear it on the wrist. Sadly i was not able to find a Housing which could be used for the Clock, so i created one myself in OpenSCAD and 3D-printed it. After a while i got tired to explain the BCD code to everybody, so there is also a Analogish Version available.

The Software for both Versions is unified and just differentiated by the Linker. So there is no change to the Code needed.

After some problems with sweat entering the Housing and destroying the electronics, i tried several possible solutions (read more in the story).

The alternative try to solve the sweat issue was to remove the buttons completely and replace them with a G-Force sensor. As sensor the Bosch BMA456 is used, since it features various interrupt functionalities to wakeup the microcontroller and only draws a few microamps in standby.

The powerful Sensor also made some other cool features for a wrist watch. There is a Wrist Tilt detection to activate the Watchface once the user rises the arm and takes a look on the watch. Now the watch can also be turned on while only using one hand e.g. while carrying stuff.

Another cool new feature is a stepcounter, so the watch is also a (not completely sweat resistant ;-) ) fitness tracker.

The next evolution step is switching to a new more powerful controller. For this the STM32L432K Controller was chosen. This controller also features a calender in the built in RTC.

Read More:

  • 1 × STM32L432KC Microprocessors, Microcontrollers, DSPs / ARM, RISC-Based Microcontrollers
  • 1 × 32,768 kHz Crystal
  • 1 × Battery Clip
  • 1 × Resistors, Capacitors, LEDs etc...
  • 1 × Bosch BMA456

  • Analog Watch is calibrated

    sulkith10/17/2020 at 09:01 0 comments

    Calibration for the analog Version is now Working

  • Analog Watch is working

    sulkith10/05/2020 at 16:13 0 comments

    The analog watch is finally Working :-)

    Some problems with the Locking of the Ports were causing the BMA Sensor to not work.

    The solution was to change the Initialization order as follows:

    • Initialize the Ports for the LEDs, so all LEDs are Off
    • Initialize the BMA Sensor
    • Lock the Ports

    Now basic functionality is given. So it is time to test it.

  • AnalogWatch is now booting

    sulkith10/04/2020 at 13:11 0 comments

    i found the short circuit, i mixed up a 0Ohm Resistor with a Capacitor.

    After removing this capacitor it was possible to program the Watch. Sadly i noticed, that the BMA is not working....

    Seems like i might have killed it by soldering it to hot and/or to long.

    So the next Todo is to build a Soldering rig, where i can solder these little chips reproducible.

  • First Analog STM32 Watch is soldered

    sulkith09/30/2020 at 19:37 0 comments

    The first Analog STM32 PCB is soldered, but it is not yet working. something with the SWD Connection seems to be wrong or broken. Analysis is ongoing ;-)

  • Shutdown is now working with very low current

    sulkith09/30/2020 at 19:21 0 comments

    The current software was working, but had a rather high current when the controller was sleeping. The root cause of this behavior was that the SPI Pins, which are routed to the BMA Sensor, were floating.

    With the Commit this was fixed and the Watch now takes only 54.6µA in shutdown and will wake up on Wrist Tilt or double Tap

  • switched to STM32

    sulkith09/30/2020 at 19:16 0 comments

    since the ATMega328P has a lot of reserved pins there are not enough usable pins to
    supply the BMA and the 42 LEDs for the analog Version (only one Pin was missing).  I switched to the STM32 Controller. But for simplicity i started with the Binary Version. To make the PCB look more like an actual PCB i also moved the BMA Sensor to the front of the Watch right next to the CPU.

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Enjoy this project?



Blo0dygeek wrote 05/06/2019 at 08:55 point

Really adore this kind of watch, like it 

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