Arduino_code_OLIMEX_Location_Manager/olimex_ESP32-C5-EVB/NFC_DEBUG_GUIDE.md

NFC (PN532) Debugging Guide

Current Status

• Hardware: GPIO26(TX) → PN532 RXD, GPIO25(RX) ← PN532 TXD (UEXT pins 3-4)
• DIP Switches: Both OFF (HSU mode) ✓
• Power: UEXT pin 1 = 3.3V (verified), Pin 2 = GND (verified)
• Wiring: Confirmed correct
• Problem: PN532 module not responding to auto-baud probe

Why NFC Probe Fails

The firmware attempts to communicate with PN532 at various baud rates:

• 115200, 9600, 57600, 38400 baud
• Tries both GPIO26/GPIO25 and GPIO25/GPIO26 (swapped)
• At each combination: sends getFirmwareVersion() command
• Issue: No response from PN532 → returns 0x00

Prerequisites for Debugging

1. Enable Serial Output

Arduino IDE Settings (REQUIRED):

Tools → USB CDC On Boot: ENABLED
Tools → Port: /dev/ttyACM0

Rebuild and flash the firmware:

cd ~/arduino/olimex_ESP32-C5-EVB/esp32_arduino
arduino --verify --board esp32:esp32:esp32c5 esp32_arduino.ino
esptool.py --chip esp32c5 --port /dev/ttyACM0 --baud 921600 erase-flash
esptool.py --chip esp32c5 --port /dev/ttyACM0 --baud 921600 write-flash 0x0 build_output/esp32_arduino.ino.merged.bin

Open Serial Monitor:

• Arduino IDE → Tools → Serial Monitor
• Baud rate: 115200
• Wait for boot messages

Diagnostic Steps

Step 1: Verify Serial Output

Expected output during boot:

=================================
ESP32-C5 Home Assistant Device
Arduino Framework
=================================
...
--- NFC (PN532 HSU) Initialization with Debug ---
Hardware: GPIO26(TX)→PN532-RX, GPIO25(RX)←PN532-TX, DIP:HSU mode
  [1/8] Baud=115200, RX=GPIO25, TX=GPIO26 ... ✗
  [2/8] Baud=9600, RX=GPIO25, TX=GPIO26 ... ✗
  ...

If you see:

• ✓ All "✗" symbols → PN532 not responding at any baud rate
• Nothing after "Initialization" → Serial output not working (re-check USB CDC setting)

Step 2: Physical Verification Checklist

□ PN532 powered: Measure 3.3V on VCC pin (should be 3.0-3.3V)
□ PN532 GND: Verify continuity to board GND with multimeter
□ UEXT Pin 1: Should be 3.3V (measure with multimeter)
□ UEXT Pin 2: Should be GND (continuity check)
□ UEXT Pin 3 (GPIO26): No continuity to Pin 4 (should be separate signals)
□ UEXT Pin 4 (GPIO25): No continuity to Pin 3 (should be separate signals)
□ PN532 Module: Try re-seating in connector or using different PN532 board

Step 3: Signal Analysis (Advanced)

If serial output shows all "✗" but hardware checks pass:

Option A: Oscilloscope Check

Connect oscilloscope probe to GPIO26 (TX line)
- Should see UART signal transitions during probe
- If flat line: ESP32 not transmitting
- If signal present: PN532 not responding

Option B: Loopback Test

Connect GPIO26 (TX) directly to GPIO25 (RX) with a jumper wire
Rebuild with loopback test code (at end of this file)
If loopback works: GPIO pins OK, PN532 module is issue
If loopback fails: GPIO configuration issue

Possible Issues & Solutions

Issue 1: PN532 Module Defective

Symptoms: All baud rates fail, hardware verified correct Solution:

• Try different PN532 board if available
• Test with I2C mode (different DIP setting) if supported
• Replace PN532 module

Issue 2: UEXT Connector Loose

Symptoms: Intermittent detection or complete failure Solution:

• Fully remove and re-seat PN532 in UEXT connector
• Ensure connector is fully inserted until it clicks
• Check for bent pins on UEXT connector

Issue 3: Incorrect Pin Mapping

Symptoms: Detection works with swapped pins Solution:

• Edit esp32_arduino.ino:
  • Find: #define NFC_TX_PIN 26 and #define NFC_RX_PIN 25
  • If swapped RX/TX works: reverse these definitions
• Rebuild and test

Issue 4: Baud Rate Mismatch

Symptoms: Serial output shows some attempts as "✓ FOUND!" but then fails to init Solution:

• Firmware will re-init with confirmed baud rate
• If fails at SAMConfig() step: PN532 module may be in wrong mode

Loopback Test Code

(If GPIO pins might be misconfigured):

// Add to setup() after WiFi init, BEFORE NFC init:
void setup() {
    // ... existing code ...
    
    // LOOPBACK TEST
    Serial.println("--- GPIO Loopback Test ---");
    Serial.println("Jumper GPIO26 to GPIO25 to test UART");
    
    HardwareSerial testSerial(1);  // UART1
    testSerial.begin(115200, SERIAL_8N1, 25, 26);  // RX=GPIO25, TX=GPIO26
    
    delay(100);
    testSerial.print("TEST_LOOPBACK");
    delay(100);
    
    String received = "";
    while (testSerial.available()) {
        received += (char)testSerial.read();
    }
    
    if (received.indexOf("TEST") >= 0) {
        Serial.println("✓ GPIO26/GPIO25 loopback OK");
    } else {
        Serial.println("✗ GPIO loopback FAILED - pin configuration issue");
    }
}

Next Steps

1. Enable Serial Output: Change USB CDC On Boot to ENABLED
2. Rebuild & Flash: Use updated Arduino IDE settings
3. Monitor Serial: Watch boot output during NFC probe
4. Share Output: Post the serial output here for analysis

Expected Timeline:

• Checking serial output: ~5 minutes
• Physical verification: ~10 minutes
• Analyzing results: ~5 minutes
• Total: ~20 minutes to identify root cause