smartChicken: Multi-Sensor Environmental & Security System

A lightweight, event-driven application built on Zephyr RTOS for multi-sensor data collection and Bluetooth Low Energy (BLE) alert broadcasting.

Project Structure

• soft_nRF: Core sensor hub firmware utilizing cooperative and preemptive workqueues to schedule non-blocking sensor sampling and manage UART/PWM peripherals.
• soft_nRF_R: Standalone receiver node logic that scans for specific broadcasting frames and drives physical LED indicators based on alert states.
• PCBs: Design files for 3 custom boards handling solar power adaptation, battery storage, and 3.3V/5V regulated power delivery.
• 3D_prints: Mechanical manufacturing models, including a structural base support for a 24-cell PV solar panel.

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Power supply layout

Receptor board layout

Connector board layout

Power supply routes

Power supply 3D board

Connector 3D board

Receptor 3D board

Technical Specifications

1. Concurrency Contexts (main.c)

The system offloads tasks to Zephyr's workqueue framework to avoid continuous thread shifting:

• sensor_wq: Cooperative workqueue (Stack: 1024, Priority: 5) dedicated to regular, periodic sensor sampling routines.
• critical_wq: Preemptive workqueue (Stack: 1024, Priority: -4) reserved for immediate actuator responses.

2. Peripheral & Sensor Matrix

• SCD30: Interfaced via I2C (DT_NODELABEL(scd30)). It measures CO2, temperature, and humidity. Integrity is verified through a Sensirion-compliant polynomial 0x31 CRC-8 check.
• DHT11: Connected via GPIO (gpio0, pin 4). Measures environmental metrics every 5000 ms using single-wire signaling.
• PIR Sensor: Connected via GPIO (gpio1, pin 8). Polled asynchronously every 2500 ms to capture motion vectors.
• Photodiode: Monitors ambient light variations.
• Fan Actuator: Driven by hardware PWM (DT_ALIAS(pwm_led0)) with a baseline period of 40 µs.
• UART Host Link: Mapped to uart20 (RX: P1.05, TX: P1.04). Operates with a 4-byte receive buffer and a 1000 µs window timeout for ESP32 communications.

3. Thresholds & Control Hysteresis

• CO2 Threshold: Registers an alert state if carbon dioxide levels exceed 1000.0 ppm.
• Fan & Thermal Management (DHT11.c):
  • Turns ON (100% duty cycle) if Temperature > 23°C (FAN_THRESHOLD_TEMP_SUP).
  • Turns OFF (0% duty cycle) when Temperature drops below 23°C.

4. Custom BLE Alert Protocol

The transmitting hub identifies itself as "smartChicken". Discovered alerts modify a 1-byte payload packaged within a Custom Manufacturer Data sequence using Company ID 0x0D06:

Bit Index	Packet Macro Flag	Trigger Condition
Bit 0	BLE_PAQUET_TEMP_BIT	Temperature exceeds 23°C
Bit 1	BLE_PAQUET_GAS_BIT	SCD30 calculated CO2 exceeds 1000.0 ppm
Bit 2	BLE_PAQUET_ATTACK_BIT	Motion registered by the PIR sensor line

The receiver application (soft_nRF_R) scans for this explicit frame, decodes the bit field state, and directly alters the status of led0, led1, and led2.