POSA_LEAKSMS/raspberry_pi4

Leak Detection Sensor Module — Raspberry Pi 4 Model B Only

A monitoring module that reads the e-con 5C-08 resistive leak detection sensor via the GPIO of a Raspberry Pi 4 Model B. On a leak it immediately reports to the PHP API server (+ triggers an SMS), and captures an on-site photo with the Pi Camera and uploads it.

This folder is a port of a module originally written for the Raspberry Pi Zero 2 W, adapted to be Pi 4 Model B only. The GPIO (BCM) numbering scheme and the rpicam/libcamera camera stack are identical on both boards, so the sensor/capture logic is unchanged; the differences are only in the wiring/power/Ethernet/camera connector and the install environment.

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1. Files

File	Role
leak_sensor.py	Main — GPIO interrupt leak detection, periodic reporting, capture+upload on leak
config.py	Non-secret default settings (sensor/threshold/interval/camera). Loads secrets from config_local
config_local.example.py	Operational/secret value template → copy to config_local.py before use (not committed)
requirements.txt	Python dependencies (pinned)
install.sh	Pi 4 install script (air-gapped offline + online fallback)
vendor.sh	Pre-download dependencies for air-gapped use (run on build machine)
test_connection.py	Server connection/signature check
systemd/leak-sensor.service	Auto-start-on-boot service unit

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2. Hardware (based on Pi 4 Model B)

• Raspberry Pi 4 Model B (BCM2711) + Raspberry Pi OS Bookworm 64-bit
• e-con 5C-08 leak detection sensor (resistive, high-impedance ~1.5MΩ)
• External 4.7MΩ pull-down resistor (required — internal pull resistor is off)
• (Optional) Pi Camera — Pi 4 = 15-pin (1.0mm pitch) standard CSI, Zero 2 W = 22-pin (0.5mm pitch) CSI → Ribbon/camera boards are not compatible (a Pi 4 15-pin ribbon or a 15↔22 adapter is required)
• Power: USB-C 5V/3A (a power margin is recommended when using the camera)
• Network: Pi 4 Gigabit Ethernet (wired) or WiFi

2.1 Pinout (default single sensor)

Signal	BCM	40-pin header physical pin
Sensor input	GPIO17	11
3.3V	—	1
GND	—	6 (or 9/14/20/25/30/34/39)

To add a sensor, add an entry by BCM number to SENSORS in config.py. (e.g. GPIO27=physical pin 13, GPIO22=physical pin 15)

2.2 Electrical design (important)

• ACTIVE_LOW = False: when dry GPIO=LOW(0), on leak GPIO=HIGH(1)
• USE_INTERNAL_PULL = False (keep PUD_OFF): if you turn on the internal 50kΩ pull-down, the 1.5MΩ sensor cannot pull GPIO up to HIGH, causing detection failure. Use only the external 4.7MΩ pull-down.

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3. Server compatibility (must verify)

This module reports to a server that receives the leak_alert / leak_recovery events and photo_upload.php.

✅ The php/ server in this repo is exactly that server (single-server integration complete). Both module 1 (leak + camera) and module 2 (SHT30 temperature/humidity) report to the same cafe24 php/ server with the raw-body signature X-Signature = lowercase_hex(HMAC-SHA256(key=API_KEY, msg=request body bytes)), and leak status, photos, and temperature/humidity are shown together on a single dashboard (dashboard.php).

• New install: run only sql/schema_sht30.sql — the leak elements (leak_sensor_log.is_leak / leak_sensor_status.is_leak columns, leak_incident, leak_photo, leak_ingest_nonce tables) are already included.

Set API_URL / PHOTO_UPLOAD_URL in config_local.py to this integrated server, and make API_KEY byte-for-byte identical to the API_KEY in the server's config.local.php.

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4. Installation

4.1 Prepare configuration values

cp config_local.example.py config_local.py
# Open config_local.py and fill in API_URL / PHOTO_UPLOAD_URL / API_KEY / DEVICE_ID

If config_local.py is missing, execution stops immediately with a clear error (fail closed). Never commit config_local.py or API_KEY (they are handled by .gitignore).

4.2 Online install (environment with internet)

chmod +x install.sh
./install.sh

4.3 Air-gapped offline install

On a machine with internet of the same architecture (aarch64, ideally the same Pi 4 + Bookworm 64-bit), first fetch the dependencies to build a bundle, then move it to the target Pi 4 to install.

# (build machine, internet YES) create wheelhouse/ + debs/
./vendor.sh

# After copying wheelhouse/ and debs/ into this folder on the target Pi 4:
# (target Pi 4, internet NO)
./install.sh        # if debs/ · wheelhouse/ exist, installs offline automatically

If debs/ exists, install.sh installs offline with dpkg; if wheelhouse/ exists, it installs offline with pip --no-index. It falls back to internet apt/pip only when neither is present. wheel/deb are architecture-dependent, so ones fetched on an x86_64 PC will not work on the Pi 4.

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5. Running

source venv/bin/activate
python3 leak_sensor.py

In an environment without RPi.GPIO (a development PC, etc.), it automatically runs in simulation mode.

Connection check

source venv/bin/activate
python3 test_connection.py

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6. Auto-start on boot (systemd)

# Assumes the folder is placed at /home/pi/raspberry_pi4 (if different, edit the path in .service)
sudo cp systemd/leak-sensor.service /etc/systemd/system/
sudo systemctl daemon-reload
sudo systemctl enable leak-sensor
sudo systemctl start leak-sensor
sudo systemctl status leak-sensor
journalctl -u leak-sensor -f

SupplementaryGroups=video is required for camera access.

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7. Security notes

• Secret values (API_KEY), the server URL, and device info live only in config_local.py (not committed). Committed files contain only placeholders.
• The report body is protected against tampering with a raw-body HMAC signature: X-Signature = lowercase_hex(HMAC-SHA256(key=API_KEY, msg=request body bytes)) (leak_sensor.sign_raw ↔ server config.php::verify_signature_raw, same scheme as module 2).
  • The canonical string for the photo upload signature is device_id|sensor_id|log_id|timestamp (no spaces) (see config_local.example.py).
  • The old sha256(API_KEY + sorted JSON) body-field signature is deprecated, and the server default rejects it (ALLOW_LEGACY_BODY_SIGNATURE=false, php/config.php).
• If config_local.py is exposed, immediately rotate API_KEY (change it on the server at the same time).