Probe

TempSensor

A wireless temperature monitoring system: small battery-powered probes broadcast temperature, humidity, and battery level over BLE, and a Wi-Fi-connected hub collects those readings and uploads them to a webhook.

 ┌──────────┐   BLE advertising    ┌──────────┐   Wi-Fi (HTTPS POST)   ┌──────────────┐
 │  Probe   │  - - - - - - - - - -▶│   Hub    │ ──────────────────────▶│   Receiver   │
 │ (nRF52)  │   TEMP-XXXXXX        │ (ESP32C6)│  JSON batches          │ (your server)│
 └──────────┘   ~1 s bursts        └──────────┘  adaptive schedule      └──────────────┘

Components

Probe (Probe/)

A custom battery-powered sensor board (KiCad design in Probe/hardware/, currently developed on an nRF52 Development Kit) running Zephyr RTOS.

• Reads temperature and humidity from an SHT4x sensor over I²C, plus battery voltage through the ADC.
• Stays asleep most of the time to protect battery life. It wakes about once a minute (±5 s jitter), and only turns the radio on when something is worth reporting: either the temperature moved ≥0.2 °C since the last broadcast, or an hourly heartbeat is due (TransmissionPolicy).
• Broadcasts a compact 14-byte manufacturer-data block via BLE advertising — no pairing, no connection. Each probe identifies itself with a name like TEMP-5A6B7C derived from its own BLE address.

The board is a two-layer, button-cell-powered design built in KiCad (Probe/hardware/): an MDBT42Q nRF52 module with a PCB antenna, an SHT40 sensor, a spring-contact coin-cell holder, a programming header, and a power switch.

PCB layout (top view)	3D render

Hub (Hub/)

A Seeed XIAO ESP32C6 running Arduino firmware.

• Continuously scans for probe advertisements, decoding and deduplicating readings from up to 50 known probes (by sensor ID + sequence number).
• Buffers up to 500 readings in RAM and uploads them in bounded batches over Wi-Fi to a configurable URL. Upload scheduling is adaptive: every 15 s when healthy, faster under queue backlog, with exponential backoff after failures. Readings are only removed from the queue after the server accepts them.
• Shows live status (sensors, queue, upload counters) on an onboard ST7789 display.
• On first boot (or after a 3-second BOOT-button hold clears the config) it opens a Wi-Fi access point with a captive portal to enter your network credentials and destination URL.
• Uses the external U.FL antenna via the board's RF switch.

Shared protocol (Probe/lib/tempsensor_protocol/)

The on-air message layout is defined once, in Probe/lib/tempsensor_protocol/src/tempsensor_protocol.hpp, and consumed by both firmwares (the Hub pulls it in through a PlatformIO file:// library dependency). The probe encoder and hub decoder can therefore never drift apart; changing the layout means bumping kProtocolVersion and reflashing both sides.

The hub POSTs JSON of the form {hub_mac, hub_rssi, readings: [{timestamp, sensor_id, sequence, temperature, humidity, battery_mv, ble_rssi}, ...]}. The receiving server is not part of this repository and must deduplicate per reading by (hub_mac, sensor_id, sequence, timestamp).

Getting started

Requires PlatformIO Core.

# Build the probe firmware (nRF52 DK, uploads via J-Link)
cd Probe && pio run && pio run --target upload

# Build the hub firmware (XIAO ESP32C6, uploads over USB serial)
cd Hub && pio run && pio run --target upload

# Watch serial output (115200 baud)
pio run --target monitor

First hub boot with no saved configuration: connect to the hub's setup access-point, open the captive portal, and save your Wi-Fi SSID/password and webhook URL. See AGENTS.md for the full agent/developer reference (build config, test workflow, troubleshooting) and Hub/docs/ for the upload reliability and stress-testing notes.

Repository layout

TempSensor/             # repository root
├── AGENTS.md           # Developer/agent reference: builds, tests, conventions
├── Probe/              # BLE sensor firmware (nRF52, Zephyr)
│   ├── lib/tempsensor_protocol/   # Shared on-air schema (used by both sides)
│   └── hardware/       # KiCad PCB design and component models
└── Hub/                # Collector/upload firmware (XIAO ESP32C6, Arduino)
    ├── docs/           # Reliability & stress-test documentation
    └── test/           # Host-side policy tests + serial stress capture