Hand Module Sourcing and Mechanism Plan
Decision
No readily purchasable drop-in no-hole AMOLED compatible hand module was found. The design should proceed with a provisional actuator interface and mechanical space reserved for one of two realistic implementation paths:
- Preferred production path: sourced/OEM hybrid movement module from a supplier such as MMT or smartwatch ODM partner.
- Preferred prototype path: custom edge-driven “mystery dial” style mechanism using transparent annular discs or ring gears above the no-hole AMOLED.
What was found
MMT / Manufacture Modules Technologies
- URL: https://mmt.ch/smartwatch/modules/
- Strongest hybrid movement/module supplier lead.
- Offers connected hybrid smartwatch movement modules with analog hands, sensors, vibration, display options, and custom anadigit configurations.
- Likely B2B/OEM rather than hobbyist catalog parts.
- Action: contact for whether they can supply a low-profile 2-hand module compatible with a 44 mm case and a no-hole AMOLED below the hands.
MyKronoz ZeTime precedent
- ZeTime proved physical hands over a display can work, but its system appears proprietary.
- Public information says both hands had their own motor and the CPU could move the hands independently.
- The ZeTime used a TFT display with a center hole, not the no-hole AMOLED path selected here.
- Useful as proof of concept, not as a sourceable module.
Fossil / Garmin / Kronaby / Miyota hybrid precedents
- These validate the broader hybrid watch category.
- Publicly available parts are generally complete watches or proprietary movement platforms, not simple drop-in modules for independent product design.
Mystery dial / transparent disc mechanism
- Traditional “mystery watch” mechanisms move hands via transparent discs or edge-driven wheels.
- This is the cleanest no-hole-display mechanical concept: the display remains intact and hands/discs are driven from the bezel/perimeter.
- Requires custom mechanical design but avoids custom AMOLED fabrication.
Recommended mechanism architecture
Use a bezel-hidden edge drive:
- Minute hand attached to a thin transparent disc or annular ring above the AMOLED.
- Hour hand attached to a second coaxial transparent disc/ring or reduction stage.
- Drive teeth/magnetic features live near the outer perimeter under the bezel, outside the 33.55 mm active AMOLED area.
- A small center cap hides disc pivots or hand attachment features.
- Optional home/index sensors detect hand position at 12 o'clock.
Electrical implications
Keep the existing schematic blocks:
- DRV8833 driver as provisional dual-coil / dual-motor actuator driver.
- J3 4-pin connector as provisional hand-module interface.
- ESP32 controls hand correction and calibration.
- RTC provides accurate timekeeping.
Likely later changes:
- Add home/index sensor inputs if the final mechanism is software-positioned.
- Replace DRV8833 if the final module needs a lower-power watch-stepper pulse driver or a single-coil Lavet drive.
- Add current sensing or motor fault detection only if the selected mechanism benefits from it.
PCB/mechanical keepouts to reserve
- Keep the AMOLED unpierced.
- Reserve a visible/cosmetic center hub zone of 4–6 mm diameter on the display, not a through-hole.
- Reserve an annular mechanical drive zone under the bezel, roughly outside the AMOLED active diameter.
- Avoid placing tall components in the hand-drive sector.
- Keep the hand-drive motor/gear sector away from the ESP32 antenna.
- Place J3 near the chosen hand-drive sector.
Open questions for sourcing
- Can MMT or another supplier provide a 2-hand hybrid module without requiring a center-hole display?
- What minimum module height is achievable under the crystal?
- Are hands independently controllable, or time-only with periodic correction?
- Does the module expose coil terminals, a serial interface, or a self-contained movement input?
- Is a home/index sensor integrated?
- Can the module fit inside a 44 mm case with a 33.55 mm active display?