• Measure reflected light using AS7341 over I²C.
• Keep AS7341 on a connectorized optical-head interface for Rev A, not as a directly integrated bare IC.
• Keep the optical head modular for Rev A using a connectorized AS7341 + LED-ring assembly so optical geometry can be tested and revised without redesigning the main carrier PCB.
• Control high-CRI white LED ring brightness with constant-current drive.
• Record GPS coordinates using ATGM336H-class UART GPS module.
• Run local AI inference for color identification, spectral reflectance analysis, and material classification.
• Allow future AI models for vegetation, soil, nutrient deficiency, biomass, and plant-health classification.
• Display results on 2.8-inch SPI TFT LCD with touchscreen where practical.
• Use Radxa eMMC for OS/storage if available; use carrier microSD mainly for removable data export.
• Operate from 3.7 V LiPo battery, target 4000–6000 mAh.
• Treat 6–8 hour runtime as aspirational unless measured power supports it; prioritize reliable operation and accurate power-budget reporting over forcing runtime assumptions.
• Charge over USB-C.
• Report battery state-of-charge using a fuel gauge.
• Support safe shutdown and power-button behavior.
• Provide user buttons and status LEDs.
• Include expansion headers for future sensors/debug.
• Include load switches for GPS, LCD backlight, optical head, and LED ring.
• Include required test points for USB_5V, BAT, SYSBAT, 5V, 3V3, I2C, UART, SPI, LED rail, and shutdown signals.
• Include optional current-sense/test shunt footprints on the 5 V and LED rails.

Diagram

• Radxa Zero 3W, 4 GB RAM preferred.
• Prefer eMMC variant for OS/storage reliability.
• Carrier board exposes power, I²C, UART, SPI, GPIO, reset/safe-shutdown, and expansion.
• Do not rely on Radxa pin 26 until exact module revision/schematic verification.

• Modular Rev A optical-head connector carrying AS7341 I2C/power/control and LED-ring drive/control.
• AS7341 breakout/optical-head connector on I2C3 for Rev A.
• High-CRI white LED ring with PWM-controlled constant-current driver.
• Ambient light shield and fixed measurement geometry.
• Keep AS7341 electrically and mechanically isolated from LED switching noise.
• The connectorized optical head is intentional so optical spacing, shielding, LED geometry, and sensor placement can be revised without redesigning the main carrier PCB.

• ATGM336H UART GPS module on UART2.
• Optional PPS routed to a GPIO for timestamp precision.
• GPS antenna area must be kept away from Radxa Wi-Fi, switching regulators, battery, LCD flex, and LED driver.

• 2.8-inch SPI TFT LCD with resistive/capacitive touchscreen where practical.
• Status LEDs: power/charge, measurement, fault.
• User buttons: power/safe-shutdown, measurement trigger, back/menu or configurable.

• Primary: Radxa eMMC if available.
• Carrier microSD: removable measurement export, not primary OS dependency.
• microSD chip-select: Radxa pin 29 preferred.

• USB-C sink input with CC pull-downs, ESD, fuse/protection.
• 1S LiPo charger/power-path.
• Fuel gauge on I2C3.
• 5 V boost sized for Radxa peak load.
• 3.3 V regulator for peripherals.
• Load switches for GPS, LCD backlight, optical head, and LED ring.
• Optional current-sense/test shunt footprints on 5 V and LED rails.

• Battery: 1S LiPo, 4000–6000 mAh.
• Expected active load dominated by Radxa Zero 3W, LCD/backlight, Wi-Fi, and LED ring.
• Preliminary design target: 5 V boost rail capable of at least 2 A peak, preferably 2.5–3 A peak margin after validation.
• Runtime cannot be finalized until LCD backlight current, LED ring current, inference duty cycle, and Wi-Fi duty cycle are fixed.
• A 6–8 hour runtime target is aspirational; it must not drive unsafe undersizing or unrealistic power assumptions. The design priority is reliable operation, honest current budgeting, and measured runtime reporting.

• Production-intent custom carrier PCB, not loose development boards.
• SMD assembly preferred.
• Use real MPNs for active ICs/connectors and generic passives only where appropriate.
• Include test points for USB input, battery, system node, 5 V, 3.3 V, I²C, UART, SPI, LED rail, and shutdown signals.
• Plan for antenna keepout around Radxa Zero 3W wireless antenna and GPS antenna.

• Linux on Radxa OS/Debian.
• TensorFlow Lite runtime for first software path; RKNN conversion path for accelerated RK3566 NPU inference where supported.
• Device tree / Linux GPIO mapping required for I2C3, UART2 GPS, SPI3 LCD/microSD, buttons, LEDs, PWM LED brightness, load switches, and safe shutdown.
• Data schema should include timestamp, GPS fix, raw AS7341 channels, LED brightness level, AI class/result, and battery state.

• Handheld enclosure with optical head at one end.
• AS7341 and LED ring must be mechanically registered to a fixed measurement distance.
• Ambient light shield should define repeatable field of view.
• LCD/buttons accessible on front face.
• USB-C, power button, and microSD/service access accessible from enclosure edge.
• Avoid metal or battery placement near wireless antennas.
• Rev A optical head remains modular/connectorized to enable mechanical and optical iteration without main-carrier redesign.

• Use Radxa Zero 3W 4 GB as compute platform instead of Raspberry Pi Zero 2 W.
• Use AS7341 optical-head connector/breakout for Rev A to reduce 1.8 V sensor and optical package risk.
• Use a connectorized AS7341 + LED-ring assembly for Rev A to allow optical geometry iteration.
• Use constant-current LED control for repeatable reflectance illumination.
• Use a charger/power-path plus 5 V boost architecture because Radxa requires 5 V input.
• Prefer eMMC Radxa variant plus carrier/removable microSD for export.
• Use pin 29 as microSD CS; do not depend on pin 26 until verified.
• Stop after schematic wiring, ERC, and schematic review report; do not begin PCB layout until user approves the schematic.

• The carrier PCB will use Radxa Zero 3W headers/board-to-board mounting rather than implementing RK3566 directly.
• USB-C PD is not required for the first revision; 5 V USB-C sink charging is sufficient.
• LCD will be SPI, not HDMI, to reduce power and size.
• AS7341 breakout includes level shifting/regulation unless later confirmed otherwise.
• Battery pack includes basic protection, but board-level protection will still be included.

• Initial specification created from user-supplied engineering document.
• Prior compute-module recommendation incorporated: Radxa Zero 3W selected over Raspberry Pi Zero 2 W.
• 2026-07-06 design-decision update incorporated: pin 29 SD_CS, eMMC preferred, Rev A AS7341 optical-head connector, required load switches/test points/current-sense options, no layout before schematic review.
• 2026-07-06 approval update incorporated: 6–8 hour runtime is aspirational unless measured power supports it; Rev A optical head must remain modular/connectorized; stop after schematic review report until user approves layout.