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 (with mitxela's rounded tracks plugin), 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 ~1.5 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 |
| 8.2 pF capacitor | 0603 | 2 | 1276-2350-1-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 crystal | 1-ish mm diameter, 4.3-ish mm long | 1 | X1125-ND |
What is not included in the BOM is a CR2032 battery, which you will need to solder short wires to (I recommend getting one of those which have pre-welded contacts on the terminals, to which you will then solder to – if you cannot find any of these easily, I have had good experience with Varta CR2032s having a solder-friendly surface, just don't heat them up for too long).
The positive and negative wires of the battery should be soldered to the bottom two pads.
The tinyWatch's firmware is written in C, so you'll need the AVR port of GCC (on Arch Linux, install avr-gcc, avr-binutils and avr-libc)
Bulding the firmware is as easy as running the following command:
make all REVISION=2NOTE: The current hardware in this repository is revision 2. The old hardware (without the external crystal) is revision 1.
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:
make run REVISION=2After 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.
After a few hours/days of usage, you might notice that the clock drifts. 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 (default is 8163). With the left and right button, you may 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.
The calibration value is stored in EEPROM, so it should remain even after a battery replacement.
That's it! Enjoy your watch. More features (including a serial monitor with text input) coming soon ;)