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Add hall sensor circuit design, NTAG5 config check tool, I2C bus docs

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- 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>
This commit is contained in:
michael
2026-03-03 14:06:11 -08:00
parent e4195d2583
commit db492050e3
8 changed files with 874 additions and 50 deletions
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93
README.md
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@@ -10,26 +10,29 @@ A battery-free subdermal LED implant that harvests energy from an NFC field. An
I2C (0x30)
Phone/Reader ))) NFC ((( NTAG5Link ---------> LP5562 -----> RGBW LEDs
| | |
| VOUT | FD pin | EN
| (EH) | |
v v |
+--SAMD21E--+ |
| D0/A0 ----------------+ (GPIO enable)
| A4/A5 (I2C bus) ------+
| GPIO <--- Hall Sensor
+----------+
| VOUT | FD pin | EN (wired-AND)
| (EH) | | |
v v | |
+--SAMD21E--+ | |
| D0/A0 (open-drain) ---+ |
| A4/A5 (I2C bus) ------+ |
| EIC <--- Hall Sensor ---+ (open-drain)
+----------+ |
Rpull-up (1M)
|
VCC
```
All power comes from NTAG5Link energy harvesting — no battery.
## Components
| Component | Part | Role | I2C Addr | Key Specs |
|-----------|------|------|----------|-----------|
| 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 |
| MCU | SAMD21E18A | Firmware (Rust), pattern loading, sleep/wake | — | 256KB flash, 32KB RAM, ARM Cortex-M0+, 32-pin QFN |
| LED Driver | TI LP5562 | RGBW LED control with autonomous patterns | 0x30 | 4ch RGBW, 3 execution engines, 16 cmds/engine, 0-25.5mA/ch |
| Recovery | Hall effect sensor | Safe mode / recovery trigger | — | GPIO input with EIC wake from sleep |
| Component | Part | Role | I2C Addr | Key Specs |
| --------------- | ------------------------------------ | --------------------------------------------------- | ------------ | ---------------------------------------------------------- |
| 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 |
| MCU | SAMD21E18A | Firmware (Rust), pattern loading, sleep/wake | — | 256KB flash, 32KB RAM, ARM Cortex-M0+, 32-pin QFN |
| LED Driver | TI LP5562 | RGBW LED control with autonomous patterns | 0x30 | 4ch RGBW, 3 execution engines, 16 cmds/engine, 0-25.5mA/ch |
| Recovery + Swap | Hall effect sensor (e.g. TI DRV5032) | Pattern cycling, recovery trigger, hardware EN kill | — | Open-drain, active-low, omnipolar, <2µA quiescent |
**Dev board**: Seeed XIAO M0 (SAMD21G18A) + LP5562EVM + MikroElektronika NTAG5 Link Click
@@ -38,13 +41,14 @@ All power comes from NTAG5Link energy harvesting — no battery.
### Boot Sequence
1. NFC field detected by NTAG5Link
2. VOUT powers SAMD21E and LP5562 (MCU drives EN pin high on D0/A0)
3. SAMD21E boots, checks hall sensor GPIO (asserted = recovery mode)
4. Normal boot: reads LED pattern from NTAG5Link EEPROM via I2C
5. Programs LP5562 execution engines with pattern data
6. Enters STANDBY sleep (~5uA)
7. LP5562 runs patterns autonomously using internal oscillator
8. NFC field drops → VOUT drops → clean power-off
2. VOUT powers SAMD21E; pull-up asserts LP5562 EN (unless hall sensor is active)
3. SAMD21E boots, reads hall sensor GPIO
4. If hall asserted → **boot-time recovery** (see Recovery Mode below)
5. Normal boot: reads LED pattern from NTAG5Link EEPROM via I2C
6. Programs LP5562 execution engines with pattern data
7. Enters STANDBY sleep (~5µA)
8. LP5562 runs patterns autonomously using internal oscillator
9. NFC field drops → VOUT drops → clean power-off
### Pattern Update Sequence
@@ -57,25 +61,37 @@ All power comes from NTAG5Link energy harvesting — no battery.
7. Reprograms LP5562 engines with new pattern
8. Returns to STANDBY sleep
### Recovery Mode
### Hall Sensor Interaction
If the hall sensor is asserted at boot (magnet held near implant):
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.
**Pattern Swap (tap <1s):**
1. Magnet near → hall pulls EN low → LEDs off instantly (hardware)
2. MCU wakes via EIC interrupt, starts timer
3. Magnet removed → MCU re-asserts EN (pin high-Z, pull-up takes over)
4. Loads next stored pattern → LEDs back on
**Boot-time Recovery:**
If the hall sensor is asserted when the MCU powers up (magnet was present before NFC field arrived):
- LP5562 EN held low by hardware (LEDs never turn on)
- Loads a hardcoded default pattern (solid white, low brightness)
- Ignores EEPROM pattern data
- Sets recovery flag in SRAM for phone app detection
- Remains awake for firmware update if supported
**Hardware Safety:** Even if the MCU firmware crashes, holding a magnet near the implant forces the LEDs off at the circuit level.
## Power Budget
All power from NTAG5Link energy harvesting. Budget is constrained and TBD pending prototype measurements.
| Parameter | Value | Notes |
|-----------|-------|-------|
| EH max current | ~12.5mA | Highest threshold setting |
| EH voltage | 3.0V | Required for LP5562 (2.7-5.5V) and SAMD21E (1.62-3.63V) |
| LP5562 per channel | 0-25.5mA | Must limit to ~2-5mA/ch for EH budget |
| SAMD21E active | ~3-5mA | During boot and pattern programming |
| SAMD21E standby | ~5uA | After LP5562 engines are running |
| Parameter | Value | Notes |
| ------------------ | -------- | ------------------------------------------------------- |
| EH max current | ~12.5mA | Highest threshold setting |
| EH voltage | 3.0V | Required for LP5562 (2.7-5.5V) and SAMD21E (1.62-3.63V) |
| LP5562 per channel | 0-25.5mA | Must limit to ~2-5mA/ch for EH budget |
| SAMD21E active | ~3-5mA | During boot and pattern programming |
| SAMD21E standby | ~5uA | After LP5562 engines are running |
## Getting Started
@@ -112,13 +128,16 @@ cargo hf2 --release
Current prototype (XIAO M0 + LP5562EVM):
| XIAO Pin | LP5562EVM | Function |
|----------|-----------|----------|
| A4 (SDA) | SDA | I2C data |
| A5 (SCL) | SCL | I2C clock |
| D0/A0 | EN | Hardware enable (GPIO) |
| 3V3 | VCC | Power |
| GND | GND | Ground |
| XIAO Pin | Connection | Function |
| --------- | --------------------------- | ------------------------------------------- |
| A4 (SDA) | LP5562 SDA, NTAG5 SDA | Shared I2C data |
| A5 (SCL) | LP5562 SCL, NTAG5 SCL | Shared I2C clock |
| D0/A0 | LP5562 EN line (open-drain) | Hardware enable, wired-AND with hall sensor |
| TBD (EIC) | Hall sensor output | Interrupt/wake + wired-AND to EN line |
| 3V3 | VCC | Power |
| GND | GND | Ground |
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.
## Project Status