DIY Compass Project
- Verified the existing baseline is present: 100 mm x 50 mm layout, 3 mm corner radius, and 4-layer stackup.
- Confirmed core parts are already in place and should remain the baseline: J1, U1, U2, U3, U4, U5, U6, SW1, J2, H1, H2, H3, and H4.
- Verified key nets exist and are connected: VBAT_12V, VIN_PROT, +5V, +3V3, GND, I2C_SDA, I2C_SCL, RESET_N, SWDIO, and SWDCLK.
- Confirmed schematic ERC currently reports clean for floating pins, no-connect violations, missing power, single-pin nets, and undriven nets.
- Confirmed layout still has DRC work remaining: 52 airwire errors and 1 overlapping copper error.
- Confirmed project files exist for documentation: Design Notes and Firmware Starter.
- âś… Existing component selection was preserved and not restarted.
- âś… Schematic baseline and main net labels were verified.
- âś… Board baseline was verified as 100 mm x 50 mm, 3 mm corner radius, 4-layer.
- ❌ PCB placement optimization, routing, final DRC cleanup, and documentation updates are still pending.
Started implementing a plan
#Goal
- Complete final implementation steps on the FJ Cruiser Digital Compass project by verifying the schematic, finalizing PCB component placement, applying layout and routing rules, cleaning up DRC issues, and updating all project documentation, ensuring that the current baseline and pre-selected parts are preserved.
#Implementation plan
1. **Schematic and Baseline Verification**
1. Review the existing schematic and component connections, ensuring all key nets (e.g., VBAT_12V, VIN_PROT, +5V, +3V3, GND, I2C_SDA, etc.) remain intact.
2. Confirm that previous verification results are incorporated before proceeding with layout tasks.
2. **PCB Component Placement**
1. Place all PCB components on the 100 mm x 50 mm board per design constraints.
2. Group functional blocks:
1. Place input/power components (J1, U1) near the board edge for easy access.
2. Align U6 (seven-segment display module) for optimum dashboard viewing.
3. Isolate U5 (magnetometer) from high-noise or magnetic interfering components.
4. Arrange SW1 (calibration button) and supporting passives near associated ICs (e.g., U2, U3).
5. Position mounting holes (H1-H4) at corners with proper spacing and account for the 3 mm corner radius.
3. **Routing and Layout Rule Configuration**
1. Set and apply PCB layout rules such as trace width, clearance, and keepout/inset dimensions (0.2 mm).
2. Route remaining airwires using Auto-Route, addressing any overlapping copper issues detected earlier.
3. Run DRC/ERC checks to verify that all errors (e.g., airwires and DRC issues) have been resolved.
4. **Documentation and Project Updates**
1. Update project notes and metadata with final implementation details, component placement decisions, routing and layout rule choices, and any identified risks.
2. Archive verification status and detailed DRC cleanup actions for future reference.
#Success criteria
- The schematic remains compliant with the original design and all key nets are preserved.
- All components are correctly placed according to the grouping and positioning guidelines.
- All airwires and DRC issues are resolved with a clean DRC report.
- Project documentation is updated with final implementation notes and verification status.
Task unable to complete.
5:24:27
Task unable to complete.
5:23:46
Reviewed schematic baseline and current layout violations
0:27
Failed
18:15
Diagram
Table
| Area | Decision | Rationale |
|---|---|---|
| Vehicle input | 2-position screw terminal into TPS26630RGE eFuse | Robust harness connection and protected automotive front end. |
| Main rail | LMR50410-Q1 fixed 5V buck | Automotive-qualified wide-input buck for vehicle accessory line. |
| Logic rail | MIC5504 3.3V LDO from 5V | Keeps MCU and magnetometer on a quieter 3.3V rail. |
| MCU | ATSAMD21G18A-AU | 3.3V MCU with enough I2C/GPIO for compass, display, button, and debug. |
| Magnetometer | MMC5883MA | I2C 3-axis magnetic sensor for heading measurement. |
| Display | TM1637 4-digit seven-segment module | Integrates LED driver and digits, simplifying dashboard display wiring. |
| User input | Momentary calibration button | Enables in-vehicle hard/soft iron calibration after installation. |
| Mechanical | Four M3 non-plated mounting holes | Supports dashboard bracket or enclosure retention. |
| Board outline | 100 mm x 50 mm rectangle with 3 mm corner radius | Matches the approved dashboard compass mechanical target. |
| Stackup target | Standard 4 Layer with layer 2 as GND reference and layer 3 as power distribution | Automotive dashboard EMI environment and switching regulator benefit from continuous ground reference. |
| Layout rules | 0.2 mm board inset/keepout and 0.25 mm default trace width with 0.20 mm minimum trace width | Baseline manufacturable rules for a compact four-layer prototype. |
Table
| Net | Function | Verification status |
|---|---|---|
| VBAT_12V | Vehicle accessory input from dashboard harness. | Present in schematic baseline. |
| VIN_PROT | Protected input after eFuse. | Present in schematic baseline. |
| +5V | Buck output for display and LDO input. | Present in schematic baseline. |
| +3V3 | MCU, magnetometer, I2C pullups, debug header. | Present in schematic baseline. |
| GND | Common return and reference plane. | Present in schematic baseline. |
| I2C_SDA / I2C_SCL | MCU to magnetometer bus with 4.7k pullups. | Present in schematic baseline. |
| DISP_CLK / DISP_DIO | MCU to TM1637 display module through 100 ohm series resistors. | Present in schematic baseline. |
| CAL_BTN | Button input with pull-up. | Present in schematic baseline. |
| SWDCLK / SWDIO / RESET_N | Debug/programming signals. | Present in schematic baseline. |
Table
| Functional block | Placement decision |
|---|---|
| Vehicle input | J1 is placed at the left edge for dashboard harness access. |
| Protected input and power conversion | U1, U2, U3, L1, associated capacitors, and enable/configuration resistors are grouped on the left/lower-left side near J1. |
| Display | U6 is placed prominently along the upper/front viewing region and centered for dashboard visibility. |
| MCU | U4 is placed center-right to support short runs to display, magnetometer, button, and programming header. |
| Magnetometer | U5 is placed on the right side, separated from J1, U1, U2, L1, and the high-current display path to reduce magnetic/noise coupling. |
| Calibration button | SW1 is placed near an accessible lower edge and close enough to U4 for simple routing. |
| Programming header | J2 is placed near the right edge for access while avoiding the magnetometer-to-power-section path. |
| Mounting holes | H1-H4 are placed at the four corners with clearance for the 3 mm corner radius. |
Table
| Check | Result |
|---|---|
| Component baseline | Preserved. No component reselection or replacement was performed during final implementation. |
| Schematic ERC | Passing for floating pins, no-connect violations, missing power, single-pin nets, and undriven nets at the time of final verification. |
| Missing footprints | Passing at the time of final verification. |
| Board setup | 100 mm x 50 mm rectangle, 3 mm corner radius, Standard 4 Layer stackup, 0.2 mm inset/keepout applied. |
| Placement | All 31 PCB components placed on the top layer according to functional blocks. |
| Routing | Automated routing improved the board only partially and then stalled. The current layout still has unrouted connections and copper cleanup items, so manual follow-up or a later routing pass is still required. |
| Manufacturing readiness | Not ready for fabrication until routing completes and the final layout review is clean. |
- Re-applied the approved 100 mm x 50 mm layout shape with 3 mm corner radius.
- Re-applied the Standard 4 Layer stackup with a continuous GND reference layer and power distribution layer.
- Applied 0.2 mm keepout/inset and 0.25 mm default trace width rules.
- Re-placed all components by functional block with top-side placement.
- Re-optimized placement with explicit constraints: J1 on the left edge, U6 on the upper viewing edge, U4 center-right, U5 in the right-side quiet region, J2 upper-right, and SW1 on the bottom edge.
- Attempted full automated routing twice; the routing job did not complete.
- Attempted constrained routing with priorities for VBAT_12V, VIN_PROT, +5V, +3V3, GND, I2C, display, debug, reset, and calibration nets; the router stopped before completion and left remaining cleanup items.
- Applied net-specific power trace targets before a follow-up routing pass: VBAT_12V/VIN_PROT/SW_5V at 0.6 mm, +5V at 0.5 mm, and +3V3 at 0.35 mm.
- A later routing attempt rolled back to the better prior state because the new result was worse.
- Finish routing remaining airwires, prioritizing power rails first, then I2C, display, debug, reset, and button nets.
- Remove floating copper/via artifacts left from partial routing attempts before fabrication.
- Resolve the remaining overlapping copper items before generating manufacturing outputs.
- After routing is complete, re-run layout review and archive a clean result.
- Verify the final eFuse configuration resistor values and load-dump strategy against the TPS26630 datasheet.
- Confirm final MMC5883MA register settings and I2C address against the datasheet before production firmware release.
- Add brightness input from vehicle dimmer line if the installation harness exposes a safe, scaled dashboard illumination signal.
- Place the magnetometer away from the buck inductor, input connector, display current paths, and any steel bracket hardware.
- Mount and calibrate the board in its final dashboard location because the vehicle body, dash frame, speakers, harnesses, and aftermarket accessories create hard-iron and soft-iron errors.
- Use the four M3 mounting holes for a plastic or non-magnetic bracket where possible.
- Keep the display at the visible edge of the board with no tall components blocking viewing angle.
- Route the 12V input and buck switching loop compactly with wider traces and strong local decoupling.
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