A simple ATtiny1614-based wristwatch with an OLED display, a couple of buttons and a CR2032 battery.
To build your very own tinyWatch, you'll need to source the components, get a PCB made (or make it yourself, if you're brave enough), get the plastic parts 3D printed (or, again, print it yourself if you've already got a printer) and find a compatible 18 mm wrist strap + push pin (or edit the .scad files if you've got some other one).
The plastic parts of the tinyWatch are expected to be 3D printed (tested FDM, but SLA should work as well). They consist of:
- the back piece where the battery and PCB will be fit
- the front piece which will hold the OLED panel as well as the buttons in place, it also contains a pair of holes at each end for fitting a wrist strap push pin
- OLED support piece which will make the panel not fall inside of the watch
- 3x button caps
You can find these in the hw/3D directory in .stl format with the .scad source files are available as well.
These parts are held together with an M3 nut and M3x6 screw.
The circuit diagram as well as the PCB were designed in KiCad, the project files are available in the hw/kicad directory. Many prototype PCB manufacturers support uploading raw KiCad files directly without the need to generate Gerber files. Recommended PCB thickness is 1.6 mm.
Of course, you will then need to populate the manufactured PCB with components. The bill of materials is available here in CSV format. In summary, you'll need:
| Component | Package | Qty | DigiKey Part Number |
|---|---|---|---|
| 4.7 μF capacitor | 0603 | 1 | 1276-1044-1-ND |
| 1 μF capacitor | 0603 | 5 | 1276-1946-1-ND |
| 2.2 μF capacitor | 0603 | 1 | 1276-1040-1-ND |
| 10 μF capacitor | 0603 | 1 | 1276-1119-1-ND |
| 1N4148W diode | SOD-123 | 1 | 311-4.70KHRTR-ND |
| 4-pin straight female header | 4x2.54 pitch | 1 | S7037-ND |
| SSD1306 128x64 0.96" OLED panel | 30 pin flat ribbon, 0.7 mm pitch | 1 | 3190-DLC0096DNOG-W-5-ND (but you can probably get it much cheaper elsewhere) |
| 910k resistor | 0603 | 1 | 13-AC0603FR-07910KLTR-ND |
| 4.7k resistor | 0603 | 1 | 311-4.70KHRTR-ND |
| Push button | 6.7x4.1 mm | 3 | CKN12330-1-ND |
| ATtiny1614 | SOIC-14 | 1 | ATTINY1614-SSN-ND |
| 32.768 kHz oscillator | 3.2x2.5 mm | 1 | 50-ECS-327TXO-30-CT-ND |
What is not included in the BOM is a CR2032 battery, with specially shaped nickel strips welded to its terminals. The assembly instructions below go into more detail on how to prepare and connect the battery correctly.
The hardware assembly instructions are available in a separate document.
Please note that the document already assumes that you have already assembled the required components onto the tinyWatch mainboard (excluding the battery).
The tinyWatch's firmware is written in Rust, so you'll need the Rust toolchain to be installed.
Bulding the firmware is as easy as running the following command:
cargo build --releaseNOTE: This firmware is currently only compatible with revision 2 hardware. The old revision 1 hardware is only supported by the old C-based firmware.
If you have a serialupdi programmer attached to the PC as well as the watch and want to upload the firmware to the watch, run the following:
avrdude -p attiny1614 -c serialupdi -P /dev/ttyUSB0 -v -U flash:w:target/avr-none/release/tinywatch.elfThe watch consumes roughly 4.4 mA while the screen is on, and about 3.4 μA while the screen is off.
If you look at your watch for a total of 5 minutes each day, that would result in about 447 μAh of power consumption per day. With this usage, the 220 mAh battery in the watch should last more than a year.
These measurements were taken using Nordic's Power Profiler Kit 2. The raw capture file can be viewed in the Power Profiler applet of the free and open source nRF Connect for Desktop software.
After flashing the firmware, you will want to set up the clock. To do that, press the left and right button at simultaneously. Then, using the left and right button, you will set the value on-screen and then press the middle button to confirm your selection and move onto the next value or finish the clock setup if you're done. You will be asked at the end whether the entered values are correct.
Note
Revision 2 hardware uses a high quality temperature-compensated crystal oscillator with at most ±5 ppm of error, resulting in less than 0.5 seconds of drift per day. With this hardware, this option should be left alone.
If you experience severe drifts with the watch (more than 1 second per day), it is possible to trim the oscillator to a more precise value.
To remedy this issue, press the left and middle button together to enter the clock calibration menu. There, you will be presented by a 16-bit hex value (the default is 8000, corresponding to the 32.768 kHz of the main oscillator). With the left and right button, you can move the cursor.
To edit a value of a digit, press the middle button (the cursor will appear above the digit so that it is apparent what the buttons currently do) and adjust the value using the left and right button.
To confirm your choice, press the middle button again to go back to cursor mode. Choose Done and press the middle button to exit.
Once your watch is set up with the correct time, it is now ready to serve your everyday needs of checking the time. Simply push any of its buttons and it will light up for a few seconds to tell you the time, before turning off again to conserve power.
That's it! Enjoy your watch. More features coming soon ;)