DIY Dashboard Compass Project
0:23
Explaining ongoing projects.
You’re right to ask. The short version: I made real progress, but the work got interrupted multiple times by execution stops, so it likely looked like I was spinning.
Here’s what actually happened:
Table
| Area | What I did | Current state |
|---|---|---|
| Project setup | Renamed the project and updated the description to match the FJ Cruiser solar compass concept | Done |
| Architecture notes | Created Design Notes for the system intent | Done |
| Major components | Added the MCU, magnetometer, LED driver, charger, LDO, displays, dimmer/switch, connectors, protection, and passives | Done |
| Power wiring | Wired solar input through fuse, Schottky reverse protection, TVS clamp, charger input, battery, charger SYS output, switched rail, and 3.3V LDO | Mostly done |
| Logic wiring | Wired I2C between U1, U2, and U3, with pullups | Done |
| Display wiring | Wired the three 7-segment displays to the LED driver segment/common nets | Done |
| Dimmer/off | Wired RV1 as both ADC dimmer input and hard load-disconnect switch | Done |
| Debug/reset | Wired SWD/debug and reset support around U1 and J3 | Done |
| Display replacement | Replaced the earlier placeholder displays with DISP1, DISP2, and DISP3 using LTS-5503AE orange/yellow displays, then rewired them | Done |
| Board setup | Set the layout to a 120 mm x 55 mm rounded rectangle, 4-layer stackup, 0.2 mm keepout, and 0.25 mm trace width | Done |
| PCB placement/routing | Started moving toward layout work, but placement and routing were interrupted before completion | Not done |
The biggest reason it took so long is that the execution agent was stopped several times, including by “insufficient credits” earlier and later by “stopped by user.” I did not get all the way through PCB placement, routing, DRC review, or manufacturability review.
Most important unfinished items
- Run a schematic review/ERC to catch floating or incorrectly configured pins.
- Verify charger/programming resistor values against the actual solar panel and battery you want to use.
- Place components on the PCB.
- Route the board.
- Run DRC and review footprints/MPNs.
I should have surfaced the interruptions more clearly instead of leaving you guessing.
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Design Notes
Project
Dashboard-mounted automotive compass for Toyota FJ Cruiser.
Architecture decisions
- Use a 3-axis I2C magnetometer for heading sensing.
- Use a low-power MCU to read the compass, compute N/E/S/W/NE/NW/SE/SW text, read dimmer voltage, and control display brightness.
- Use an I2C LED display driver to reduce MCU pin count for three amber/yellow 7-segment digits.
- Use a single-cell LiPo energy store with solar charging and 3.3V regulation.
- Use a switch-pot dimmer as both user brightness control and hard/off input.
- Include automotive-style input protection and decoupling even though the main charge source is solar.
Schematic wiring completed
- Solar input path: J1 pin 1 -> F1 -> D2 -> CHG_IN -> U4 IN.
- Input protection: D1 TVS and C7/C5 capacitance from CHG_IN to GND after reverse protection.
- Battery path: U4 BAT -> J2 pin 1 with C12 BAT bypass to GND.
- System path: U4 SYS -> RV1 switch -> U5 input -> 3.3V logic rail.
- Dimmer: RV1 potentiometer forms a 3.3V to GND divider; wiper goes to U1 PA02 as DIMMER_ADC.
- I2C bus: U1 PA22/PA23 connect to U2 and U3 with R1/R2 4.7k pull-ups to 3.3V.
- Debug: J3 follows ARM 2x5 SWD convention with VTref, SWDIO, SWCLK, RESET, and GND.
- Display matrix: U3 CA1-CA8 drive shared segment nets a, b, c, d, e, f, g, dp. U3 CB1-CB3 select digit commons for DISP1-DISP3.
Charger configuration
- U4 BQ25185 is configured for a protected single-cell LiPo pack.
- R3 = 6k on ISET targets about 50mA fast charge current using KISET typical 300AΩ.
- R4 = 18k on ILIM/VSET sets 4.2V battery regulation and 500mA input current limit per BQ25185 datasheet table.
- R11 currently holds TS/MR high because no battery NTC connector/network is fitted. For production, replace this with a battery NTC network or a battery pack with appropriate temperature monitoring.
- U4 ~CE is tied low so charging remains enabled while solar input is present.
Support passives added
- R5/C10: reset pull-up/filter for U1 ~RESETN.
- R6/R7: SWDIO pull-up and SWCLK pull-down.
- R8/C13: U3 R_EXT and C_FILT support network.
- R9/R10: U4 STAT1/STAT2 pull-ups for MCU monitoring.
- C11: U1 VDDCORE capacitor.
- C12: U4 BAT bypass capacitor.
- C14: U2 C1 support capacitor.
Layout intent
- Rectangular dashboard board with three displays centered and aligned for visibility.
- Dimmer/off knob placed at the right edge for driver access.
- Solar and battery connectors placed at board edges.
- Magnetometer placed away from high-current LED traces, power/protection parts, ferrous hardware, and mounting screws.
- LED driver placed near the displays to keep segment/common traces short.
- Charger, fuse, TVS, and battery connector grouped together near the power-entry edge.
Open engineering notes
- The current display parts are accepted as library-available amber/orange placeholders.
- The current switch-pot is accepted for schematic/layout progress, but its mechanical fit should be confirmed against the final dashboard enclosure.
- Add mounting holes only after confirming dashboard bracket/enclosure constraints.
- A real battery NTC network is recommended before field use if the selected LiPo pack does not already provide protected/temperature-monitored charging behavior.
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