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>
160 lines
7.5 KiB
Markdown
160 lines
7.5 KiB
Markdown
# Hall Sensor + LP5562 EN Wired-AND Circuit Design
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**Date**: 2026-03-03
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**Status**: Design in progress
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## Problem
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The implant needs a hall sensor for three functions:
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1. **Pattern swap** — quick magnet tap cycles to the next stored pattern
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2. **Runtime recovery** — long hold + confirmation tap enters safe mode
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3. **Boot-time recovery** — magnet present at power-on skips EEPROM, loads default
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4. **Hardware safety** — LEDs forced off by magnet even if MCU firmware has crashed
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These must work within extreme space and power constraints (energy-harvested implant).
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## Circuit: Wired-AND on LP5562 EN
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Zero extra active components. Hall sensor and MCU share the EN line via open-drain outputs.
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```
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VCC (3.0V from NTAG5Link EH)
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1M (pull-up resistor)
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EN ------+------- MCU D0/A0 (open-drain)
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+------- Hall sensor OUT (open-drain, active-low)
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LP5562 EN pin
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Hall sensor OUT ---- MCU EIC pin (separate connection for interrupt/wake)
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```
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### How it works
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| State | MCU pin | Hall sensor | EN line | LP5562 |
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|-------|---------|-------------|---------|--------|
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| Normal operation | High-Z | High-Z (no magnet) | High (pull-up) | On |
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| Magnet present | High-Z | Driving low | Low | Off |
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| MCU disabling LP5562 | Driving low | High-Z | Low | Off |
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| Magnet + MCU low | Driving low | Driving low | Low | Off |
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### Pull-up resistor: 1M
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- Steady-state current: ~0 (both open-drains high-Z, no path to ground)
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- Current when EN low: 3V / 1M = 3 µA (only during magnet or MCU-driven low)
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- Rise time: ~10 µs (1M x ~10pF parasitic) — instant from human perspective
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- LP5562 EN input is high-impedance CMOS — no DC loading
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## Hall Sensor: TI DRV5032
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| Variant | Use | Iq | Threshold | Output | Package |
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|---------|-----|-----|-----------|--------|---------|
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| **DRV5032FB** | Prototype | 1.6 µA | 8.4 mT (omnipolar) | Open-drain | SOT-23 |
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| **DRV5032FE** | Final PCB | 0.55 µA | 4.5 mT (omnipolar) | Open-drain | X2SON (1x1mm) |
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- **Omnipolar**: Triggers on either magnetic pole (user doesn't need to orient magnet)
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- **8.4 mT threshold (FB)**: Higher threshold = harder to accidentally trigger. Requires deliberate, close magnet interaction. Good for "don't accidentally enter recovery" requirement.
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- **Open-drain, active-low**: Required for wired-AND topology
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- **SOT-23 for prototyping**: Easy to hand-solder; X2SON for final implant PCB
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## Interaction Model
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### Pattern Swap (tap <1s)
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1. Magnet near → hall pulls EN low → LEDs off instantly (hardware, zero MCU latency)
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2. MCU wakes via EIC interrupt on hall sensor pin, starts timer
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3. Magnet removed (hall goes high-Z, pull-up restores EN)
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4. MCU detects short press (<1s) → loads next stored pattern → LEDs back on
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### Runtime Recovery (hold >3s + confirm)
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1. Magnet near → EN low (hardware), MCU wakes via EIC
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2. MCU counts hold duration while hall stays asserted
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3. Magnet removed after >3s → MCU notes "long hold detected"
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4. MCU re-enables LP5562 → blinks warning pattern (3x red flash)
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5. MCU waits 2s for confirmation tap
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6. Confirmation tap received → enters recovery mode
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7. No confirmation → resumes normal operation (reloads previous pattern)
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### Boot-time Recovery
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1. NFC field arrives, VOUT powers system
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2. Hall sensor already active (magnet was present before power) → EN held low by hardware
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3. MCU boots, reads hall GPIO → asserted → boot-time recovery
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4. Loads hardcoded default pattern (solid white, low brightness)
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5. Skips EEPROM pattern data
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6. Sets recovery flag in SRAM for phone app detection
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7. When magnet removed, EN goes high, default pattern runs
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### Hardware Safety (MCU crashed)
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- Holding magnet forces EN low at circuit level regardless of MCU state
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- No firmware dependency — pure hardware path
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- Magnet removal restores EN via pull-up (LP5562 resumes last-programmed pattern)
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## Firmware State Machine (M8)
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```
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┌─────────────┐
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power-on -->│ BOOT_CHECK │
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└──────┬──────┘
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hall low? │
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┌───yes─────┼────no───┐
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v │ v
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┌──────────┐ │ ┌─────────────┐
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│ RECOVERY │ │ │ RUNNING │<──────────────┐
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└──────────┘ │ └──────┬──────┘ │
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│ hall EIC │ │
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│ interrupt│ │
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│ v │
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│ ┌─────────────┐ │
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│ │ HALL_ACTIVE │ │
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│ └──────┬──────┘ │
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│ hall released │
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│ │ │ │
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│ <1s >3s │
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│ │ │ │
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│ v v │
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│ ┌──────┐ ┌──────────────┐ │
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│ │ SWAP │ │ WARN_BLINK │ │
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│ └──┬───┘ └──────┬───────┘ │
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│ │ hall tap │ no tap │
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│ │ in 2s? │ │
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│ │ ┌──yes ┌──no │
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│ │ v v │
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│ │ ┌────────┐ │ │
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│ │ │RECOVERY│ │ │
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│ │ └────────┘ │ │
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│ └──────────────┴──────────┘
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```
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States:
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- **BOOT_CHECK**: Read hall GPIO. If asserted → RECOVERY. Else → RUNNING.
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- **RUNNING**: LP5562 engines active, MCU in STANDBY sleep. Wakes on hall EIC.
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- **HALL_ACTIVE**: Magnet detected. Timer running. Waiting for release.
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- **SWAP**: Load next pattern, re-enable LP5562 → RUNNING.
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- **WARN_BLINK**: Blink 3x red. Wait 2s for confirmation tap.
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- **RECOVERY**: Default pattern, skip EEPROM, stay awake, set SRAM flag.
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## Power Impact
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| Component | Added draw | When |
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|-----------|-----------|------|
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| Hall sensor (DRV5032FB) | 1.6 µA | Always (quiescent) |
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| Pull-up resistor (1M) | 3 µA | Only when EN is low (magnet or MCU-driven) |
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| Pull-up resistor (1M) | ~0 | Steady state (EN high, no current path) |
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Total added quiescent: **~1.6 µA** — negligible vs LP5562 LED current (~12 mA).
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## Open Questions
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| Question | Notes |
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|----------|-------|
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| Debounce needed? | Hall sensors are usually clean (no mechanical bounce), but verify with DRV5032 |
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| EIC pin selection on SAMD21E | Must be EIC-capable for wake from STANDBY. Check SAMD21E pinout. |
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| Magnet strength/distance | What N52 neodymium size triggers DRV5032FB at implant depth (~3-5mm subdermal)? |
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| Multiple stored patterns | How many patterns to cycle through? Currently TBD (depends on EEPROM format, M5) |
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