PCB Design for Smart Ring
Worked for 36 mins 10 sec
Fixed the PCB routing issues by converting this into a wider 80 mm × 16 mm EVT prototype board.
What is now fixed:
- Widened the board and kept a 4-layer stackup.
- Deleted all stale/bad routing.
- Re-placed the full board for routability.
- Reran autoroute successfully.
- Removed leftover floating/dangling/overlap fragments.
- Final PCB DRC now has:
- 0 airwires
- 0 overlapping copper
- 0 floating copper
- 0 dangling traces
- 0 missing footprints
- 0 invalid-layer errors
Intentional design changes made to close routing:
- Removed the optional MP2662 charger INT connection.
- Left the 32 MHz crystal shield/mechanical pads unconnected.
- Marked unused U1 VBUS as intentional no-connect, though the ERC still reports it as missing power because USB is not used in this pogo-charged revision.
Still not fully assembly-ready:
- 45 generic parts still need MPNs for an assembled BOM.
- U1 VBUS ERC remains as a justified false-positive/waiver for this no-USB prototype.
Bottom line: the PCB layout is now electrically routed and DRC-clean for routing/manufacturing geometry. Next step is BOM cleanup/MPN assignment before ordering assembled boards.
how can I download this as a DXF file
Thought for 8 sec
To download a DXF from Flux:
- Open the project.
- Go to the Files / Export area.
- Choose an export option for the PCB/mechanical data.
- Select DXF if available.
- Download the generated file from the Files tab.
If you specifically need a board outline DXF for the mechanical enclosure/ring band:
- Export the PCB outline/mechanical layer as DXF.
- Use that DXF in CAD to design the enclosure, flex outline, dock, or ring carrier.
If you do not see DXF as an export option, use the manufacturing/mechanical export options available in Flux, or export Gerbers and convert the board outline/mechanical layer to DXF in your mechanical CAD workflow.
Export DXF
Export manufacturing files
Fix BOM MPNs
Run final review
Create assembly notes
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Project Specification — MinaRing Prayer Companion
Project Overview
Status: Draft architecture with prototype mechanical target updated for routability.
MinaRing is a rigid-flex BLE smart ring intended as an Islamic prayer companion device. It uses capacitive swipe/touch electrodes around the ring band, BLE connectivity, and haptic feedback from a small LRA motor.
Intended Use
- Body-worn ring form factor.
- Prototype-to-production intent, derived from a breadboard prototype.
- User interaction via capacitive swipe/touch around the circumference.
- Feedback via quiet haptic vibration.
What the Device Should Do
- Detect 4 capacitive electrode zones for swipe/touch gestures.
- Connect to a phone/app over BLE.
- Drive an LRA haptic actuator for reminders/feedback.
- Recharge a small Li-Po/Li-ion cell using a ring-suitable charging method.
- Operate at low power for wearable runtime.
Main Features
- BLE SoC: compact Nordic nRF52-class device preferred; nRF52833/nRF52840 direction pending library/datasheet availability.
- Capacitive touch: compact I2C touch controller preferred over breadboard-scale MPR121 if available.
- Haptics: DRV2605L I2C haptic driver, address 0x5A.
- Actuator: coin/bar LRA such as Vybronics VG0832013D class.
- Shared I2C bus for touch + haptic.
- Rigid-flex PCB architecture with a rigid electronics island and flexible electrode/antenna sections.
- Prototype mechanical target: 18.5 mm inner diameter, maximum 9.5 mm band width, dock-based pogo/contact charging pads.
System Architecture
Diagram
Hardware Subsystems
Compute and BLE
- Compact BLE SoC with SWD programming/debug.
- Prefer Nordic nRF52 family for firmware continuity from nRF52840 DK unless ring-scale size forces a smaller BLE SoC.
- BLE antenna requires dedicated keepout and tuning provision.
Capacitive Touch
- Four electrodes wrap around the band circumference.
- Existing prototype uses MPR121 at I2C address 0x5B.
- Ring-scale implementation should use a smaller controller if available and maintain shared I2C.
Haptics
- DRV2605L haptic driver on I2C address 0x5A.
- LRA motor output routed as a short, symmetric pair with local haptic driver decoupling.
Power
- Small rechargeable Li-Po/Li-ion cell.
- Charging direction: pogo/contact pads in a dock. Wireless charging is deferred because the coil competes with antenna, battery, and electronics volume in the first prototype.
- Low-Iq regulation and load switching should be considered for touch/haptic domains.
Programming and Test
- SWD pads required.
- Add test pads for battery, regulated rail, GND, SDA, SCL, haptic outputs, and charge status.
Interfaces and Connections
- I2C: BLE SoC master to touch controller and DRV2605L.
- SWD: SWDIO, SWDCLK, RESET, VREF, GND.
- Charging: pogo/contact dock pads.
- LRA motor: differential actuator output from DRV2605L.
- Capacitive electrodes: 4 routed flex electrodes around band.
Power and Runtime Expectations
- Runtime target not yet specified; design will prioritize low sleep current.
- Assumed battery: very small LiPo/Li-ion pouch/curved cell, likely 10–30 mAh class depending on mechanical ID/OD.
- Haptic pulses dominate peak current; BLE advertising/connection dominates radio active current.
Preliminary Power Tree and Power Budget
Table
| Rail | Load | Sleep | Typical active | Peak/transient |
|---|---|---|---|---|
| VBAT | LRA via DRV2605L | ~0 | pulse-dependent | tens of mA typical LRA pulse |
| VDD | BLE SoC | sub-uA to few uA system target | BLE events in mA range | radio TX/RX peak in mA range |
| VDD | Touch controller | low-uA target | scan-dependent | controller-dependent |
| VDD | DRV2605L logic | low-uA standby target | active I2C/control | motor drive on VBAT/VDD path |
Exact regulator/charger sizing will be finalized from selected datasheets and chosen battery.
Manufacturing and Assembly Expectations
- Rigid-flex construction: rigid electronics island plus flexible band sections.
- Fine-pitch assembly expected; WLCSP/BGA may require advanced assembly and X-ray inspection.
- For early EVT, QFN/WLCSP tradeoff should be selected based on assembler capability.
- BLE antenna tuning needs VNA validation on-body and in the final mechanical stack.
Firmware-Relevant Hardware Requirements
- I2C addresses: touch at 0x5B if MPR121 retained; haptic DRV2605L at 0x5A.
- Gesture scan and haptic patterns should support low-power sleep/wake.
- BLE OTA update support recommended if SoC memory allows.
Physical Design Expectations
- Ring band rigid-flex, with electronics concentrated in a top rigid island.
- Target inner diameter: 18.5 mm, approximately US size 8.5–9.
- Maximum band width: 9.5 mm for the first routed prototype. The original 8 mm target was too routing-constrained with the current QFN + MPR121 + charger + haptic architecture.
- Touch electrodes distributed around circumference on flex.
- Antenna isolated from battery/motor/skin-facing metal as much as possible.
- Charging pads placed on inner or underside surface for cradle contact.
Important Design Decisions
- Use pogo/contact charging pads in a cradle rather than USB or wireless charging for the first prototype.
- Preserve Nordic nRF52 direction initially for firmware continuity.
- Use a more compact touch controller if library and datasheet support are available; otherwise retain MPR121 for schematic continuity.
Assumptions
- This is a prototype/EVT design, not yet a certified production release.
- Battery dimensions and target runtime are not yet locked; ring size and charging method are now locked for the first prototype.
- Ring-scale BLE antenna requires mechanical co-design and tuning after layout.
Change Notes
- Initial specification created from user requirements.
- Locked first prototype mechanical target: 18.5 mm ID, 8 mm maximum band width, pogo/contact charging pads.
- Revised prototype band width to 9.5 mm after routing showed the 8 mm layout remained congested with unresolved airwires.
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