Solar Dashboard Compass Design
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Pre-routing found one real footprint issue at the charger: some mechanical/copper pads on U3 overlap its ground pad but aren’t assigned to the same net. I’m fixing that before routing so the autorouter doesn’t create an unsafe result.
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Thought for 5 mins 33 sec
2/5 Fix U3 charger footprint overlapping copper/net assignment before routing
Run pre-routing board validation
Fix U3 charger footprint overlapping copper/net assignment before routing
Auto-route all PCB nets
Review routed board for airwires and DRC issues
Summarize routing result and any remaining issues
Accessed knowledge.
u# has no copper overlap that I can see
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Project Specification
Project Overview
Status: Draft
A solar-powered dashboard compass for a Toyota FJ Cruiser. The device senses vehicle heading and shows the direction on three retro-style orange 7-segment displays, with rechargeable battery backup and a rotary brightness control that clicks off at the low end.
Intended Use
- Mounted on a vehicle dashboard in a high-temperature, high-vibration automotive interior.
- Solar panel maintains battery charge during daylight.
- Battery powers the compass when solar input is unavailable.
- User adjusts display brightness with a rotary knob; turning fully counterclockwise clicks the unit off.
What the Device Should Do
- Display compass heading using three 7-segment characters, e.g. N, NE, E, SE, S, SW, W, NW, or numeric bearing if firmware is configured that way.
- Use warm orange LED displays for a retro dashboard look.
- Automatically operate from solar/battery power.
- Allow manual brightness control and physical off state.
Main Features
- 3-axis magnetometer compass sensor.
- Low-power microcontroller.
- Three orange 7-segment LED displays.
- LED display driver with brightness control from MCU.
- Rotary potentiometer with integrated off switch.
- Solar Li-ion/LiPo charging and battery backup.
- Debug/programming connector and test points.
System Architecture
Diagram
Hardware Subsystems
- Power: solar input, single-cell LiPo battery, charger/power path, regulated logic rail.
- Compute: low-power MCU with I2C/SPI/GPIO and ADC.
- Sensor: 3-axis magnetometer over I2C.
- Display: 3-digit orange LED display driven by a multiplexed display driver.
- User Control: rotary potentiometer read by MCU ADC plus integrated power switch.
- Debug: programming header for firmware loading and calibration support.
Interfaces and Connections
- Solar panel connector: two-wire PV input.
- Battery connector: single-cell LiPo JST-style connector.
- Display: segment/digit drive lines from display driver.
- Magnetometer: I2C SDA/SCL plus interrupt optional.
- Brightness knob: switched system enable/off path plus analog wiper to MCU ADC.
- Programming/debug connector: MCU programming interface.
Power and Runtime Expectations
Initial design target assumes a small dashboard solar panel and single-cell LiPo. LED display current dominates active power; firmware should dim aggressively at night and optionally sleep when off.
Power Tree and Power Budget
Initial estimate before final component datasheets:
Table
| Rail | Load | Typical | Peak |
|---|---|---|---|
| 3.3V | MCU | 5 mA | 15 mA |
| 3.3V | Magnetometer | 0.2 mA | 1 mA |
| Battery/System | 7-segment LED display | 30 mA | 90 mA |
| 3.3V/System | Display driver logic | 1 mA | 5 mA |
| Total active estimate | 36 mA | 111 mA |
Power-path components should be rated for at least 200 mA continuous system load with automotive temperature margin. Final budget will be updated after part selection.
Manufacturing and Assembly Expectations
- Prototype-friendly SMD design.
- Automotive dashboard temperature and sunlight exposure should be considered.
- Use vibration-resistant connectors or strain relief for solar panel and battery.
- Include test points for battery, system rail, 3.3V, GND, I2C, and display supply.
Firmware-Relevant Hardware Requirements
- Read magnetometer over I2C.
- Calibrate hard-iron/soft-iron offsets after installation in vehicle.
- Convert heading to display text.
- Read potentiometer ADC and map to display brightness.
- Drive display through selected display driver.
- Support low-power/off behavior.
Physical Design Expectations
- Dashboard-mounted enclosure or board.
- Displays visible from driver position.
- Rotary knob accessible from front face.
- Magnetometer should be kept away from high-current LED traces, magnets, steel mounting hardware, and battery leads where possible.
Important Design Decisions
- MCU-based compass selected to support calibration and display formatting.
- Digital magnetometer selected instead of analog compass for compactness and calibration flexibility.
- LED driver selected to reduce MCU pin count and handle display multiplexing.
- Solar rechargeable LiPo architecture selected for dashboard use.
Assumptions
- Battery chemistry: single-cell LiPo/Li-ion.
- Solar panel: small 5V to 6V dashboard panel, current limited below charger rating.
- Display: three 7-segment LED modules or one 3-digit orange module.
- Direction display may be cardinal text or numeric bearing; firmware can decide final format.
- Design is prototype-intent, not automotive-qualified production hardware.
Change Notes
- Initial project specification created from user requirements.
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