db492050e3
- Hall sensor + LP5562 EN wired-AND circuit design (DRV5032FB/FE, 1M pull-up, open-drain topology) with three interaction modes: boot-time recovery, tap-to-swap, hold-to-confirm recovery - NTAG5 config check tool (tools/ntag5_config_check.py) using uFCoder library for ISO15693 transparent mode via uFR Zero reader. Supports inventory + addressed mode for multi-tag fields. - Updated DEVELOPMENT_PLAN with I2C bus management notes for LP5562 (0x30) + NTAG5Link (0x54) shared bus - Updated README with wired-AND hardware diagram, hall sensor interaction section, and updated wiring table - Updated CLAUDE.md with LP5562 EN wired-AND topology docs - Updated STATUS.md with hall sensor decisions and hardware inventory Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
150 lines
7.0 KiB
Markdown
150 lines
7.0 KiB
Markdown
# xblink
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NFC-powered LED implant using NTAG5Link, SAMD21E, and LP5562.
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A battery-free subdermal LED implant that harvests energy from an NFC field. An NTAG5Link provides power and storage, a SAMD21E microcontroller reads stored LED patterns and programs the LP5562 LED driver's autonomous execution engines, then sleeps. Patterns are updated wirelessly via NFC from a phone.
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## Hardware Overview
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```
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I2C (0x30)
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Phone/Reader ))) NFC ((( NTAG5Link ---------> LP5562 -----> RGBW LEDs
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| VOUT | FD pin | EN (wired-AND)
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| (EH) | | |
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v v | |
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+--SAMD21E--+ | |
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| D0/A0 (open-drain) ---+ |
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| A4/A5 (I2C bus) ------+ |
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| EIC <--- Hall Sensor ---+ (open-drain)
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+----------+ |
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Rpull-up (1M)
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VCC
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```
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All power comes from NTAG5Link energy harvesting — no battery.
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## Components
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| Component | Part | Role | I2C Addr | Key Specs |
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| --------------- | ------------------------------------ | --------------------------------------------------- | ------------ | ---------------------------------------------------------- |
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| NFC + Power | NXP NTAG5Link (NTP53x2) | NFC interface, energy harvesting, pattern storage | 0x54 (slave) | 2048B EEPROM, 256B SRAM, ISO15693, 1.8/2.4/3.0V EH output |
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| MCU | SAMD21E18A | Firmware (Rust), pattern loading, sleep/wake | — | 256KB flash, 32KB RAM, ARM Cortex-M0+, 32-pin QFN |
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| LED Driver | TI LP5562 | RGBW LED control with autonomous patterns | 0x30 | 4ch RGBW, 3 execution engines, 16 cmds/engine, 0-25.5mA/ch |
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| Recovery + Swap | Hall effect sensor (e.g. TI DRV5032) | Pattern cycling, recovery trigger, hardware EN kill | — | Open-drain, active-low, omnipolar, <2µA quiescent |
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**Dev board**: Seeed XIAO M0 (SAMD21G18A) + LP5562EVM + MikroElektronika NTAG5 Link Click
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## Architecture
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### Boot Sequence
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1. NFC field detected by NTAG5Link
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2. VOUT powers SAMD21E; pull-up asserts LP5562 EN (unless hall sensor is active)
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3. SAMD21E boots, reads hall sensor GPIO
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4. If hall asserted → **boot-time recovery** (see Recovery Mode below)
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5. Normal boot: reads LED pattern from NTAG5Link EEPROM via I2C
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6. Programs LP5562 execution engines with pattern data
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7. Enters STANDBY sleep (~5µA)
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8. LP5562 runs patterns autonomously using internal oscillator
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9. NFC field drops → VOUT drops → clean power-off
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### Pattern Update Sequence
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1. Phone sends new pattern data to NTAG5Link via NFC
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2. NTAG5Link signals MCU via FD pin (SRAM write indication)
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3. SAMD21E wakes from sleep via EIC interrupt
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4. Pauses LP5562 engines (set exec to Hold)
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5. Reads new pattern from NTAG5Link SRAM mailbox via I2C
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6. Writes pattern to NTAG5Link EEPROM for persistence
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7. Reprograms LP5562 engines with new pattern
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8. Returns to STANDBY sleep
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### Hall Sensor Interaction
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The hall sensor serves three purposes via a wired-AND circuit: the hall sensor (open-drain, active-low) and MCU GPIO (open-drain) share the LP5562 EN line with a pull-up resistor. When the magnet is present, EN is forced low at the hardware level — independent of MCU state.
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**Pattern Swap (tap <1s):**
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1. Magnet near → hall pulls EN low → LEDs off instantly (hardware)
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2. MCU wakes via EIC interrupt, starts timer
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3. Magnet removed → MCU re-asserts EN (pin high-Z, pull-up takes over)
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4. Loads next stored pattern → LEDs back on
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**Boot-time Recovery:**
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If the hall sensor is asserted when the MCU powers up (magnet was present before NFC field arrived):
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- LP5562 EN held low by hardware (LEDs never turn on)
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- Loads a hardcoded default pattern (solid white, low brightness)
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- Ignores EEPROM pattern data
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- Sets recovery flag in SRAM for phone app detection
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- Remains awake for firmware update if supported
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**Hardware Safety:** Even if the MCU firmware crashes, holding a magnet near the implant forces the LEDs off at the circuit level.
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## Power Budget
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All power from NTAG5Link energy harvesting. Budget is constrained and TBD pending prototype measurements.
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| Parameter | Value | Notes |
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| ------------------ | -------- | ------------------------------------------------------- |
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| EH max current | ~12.5mA | Highest threshold setting |
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| EH voltage | 3.0V | Required for LP5562 (2.7-5.5V) and SAMD21E (1.62-3.63V) |
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| LP5562 per channel | 0-25.5mA | Must limit to ~2-5mA/ch for EH budget |
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| SAMD21E active | ~3-5mA | During boot and pattern programming |
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| SAMD21E standby | ~5uA | After LP5562 engines are running |
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## Getting Started
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### Toolchain Setup
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```bash
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# Install Rust
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curl --proto '=https' --tlsv1.2 -sSf https://sh.rustup.rs | sh
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source $HOME/.cargo/env
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# Add ARM Cortex-M0+ target
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rustup target add thumbv6m-none-eabi
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# Install cargo-hf2 for UF2 flashing (XIAO M0)
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cargo install cargo-hf2
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```
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On Linux, add udev rule for XIAO bootloader (vendor ID 0x2886):
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```bash
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echo 'SUBSYSTEM=="usb", ATTR{idVendor}=="2886", MODE="0666"' | sudo tee /etc/udev/rules.d/99-xiao.rules
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sudo udevadm control --reload-rules
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```
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### Build and Flash
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```bash
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cargo build --release
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# Put XIAO in bootloader mode (double-tap RST), then:
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cargo hf2 --release
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```
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## Dev Board Wiring
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Current prototype (XIAO M0 + LP5562EVM):
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| XIAO Pin | Connection | Function |
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| --------- | --------------------------- | ------------------------------------------- |
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| A4 (SDA) | LP5562 SDA, NTAG5 SDA | Shared I2C data |
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| A5 (SCL) | LP5562 SCL, NTAG5 SCL | Shared I2C clock |
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| D0/A0 | LP5562 EN line (open-drain) | Hardware enable, wired-AND with hall sensor |
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| TBD (EIC) | Hall sensor output | Interrupt/wake + wired-AND to EN line |
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| 3V3 | VCC | Power |
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| GND | GND | Ground |
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LP5562 EN line has a 1M pull-up resistor to VCC. Both D0/A0 (open-drain) and the hall sensor (open-drain, active-low) connect to this line — either can pull EN low.
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## Project Status
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See [docs/STATUS.md](docs/STATUS.md) for current progress.
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## Related Projects
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- `../ntag5-samd21-lp562/` — LP5562 Rust driver prototype and SAMD21 test firmware
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- `../ntag5sensor/` — Python NTAG5Link tooling (PCSC reader, ISO15693, sensor interface)
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