# Sensor Node Hardware Selection

## Sensor Node Hardware Selection

Choosing the right sensor hardware determines the long-term reliability, accuracy, and maintainability of your mesh monitoring deployment. This page compares the two dominant approaches: RAK WisBlock modular sensor boards and Meshtastic telemetry running on commodity hardware such as the TTGO T-Beam.

### RAK WisBlock Sensor Modules

WisBlock is RAK Wireless's modular ecosystem: a WisBlock Core module (e.g., the RAK4631 = Nordic nRF52840 / SX1262) pairs with a WisBlock Base board such as the RAK19007 (other bases exist, e.g. RAK5005-O and RAK19003). Sensor modules snap onto the base board's sensor slots with no soldering required, making field assembly and repair straightforward.

- **RAK1906 (BME680)** - Measures temperature (±1°C), relative humidity (±3% RH), barometric pressure (±0.6 hPa), and volatile organic compound (VOC) air quality index. The BME680 gas sensor requires a burn-in period of roughly 48 hours before IAQ readings stabilise (IAQ also depends on the Bosch BSEC library and ongoing calibration). Current draw: ~0.15 µA sleep; the standard temperature/humidity/pressure measurement is in the microamp range (a few µA at 1 Hz), while the integrated gas (VOC) heater draws several mA in bursts only when VOC sensing is enabled. Ideal for indoor air quality and outdoor environmental monitoring.
- **RAK12500 (u-blox ZOE-M8Q GPS)** - Adds GNSS positioning for mobile or asset-tracking nodes. Cold-start TTFF ~29 s, hot-start ~1 s. Active current ~17-18 mA; disable when stationary to preserve battery. Compatible with external active antenna via U.FL connector.
- **RAK12004 (MQ-2 Gas Sensor)** - Detects LPG, propane, hydrogen, methane, and smoke. The MQ-2 heater (~150 mA) cannot be put to sleep and must run continuously for valid readings; duty-cycling it to save power makes gas readings unreliable until the heater re-stabilises (tens of seconds to minutes after warm-up). This ~150 mA continuous draw (~3.6 Ah/day) dominates the power budget, so the MQ-2 is poorly suited to small solar/battery nodes and should not be relied on as a life-safety combustible-gas detector.
- **RAK1901 (SHTC3)** - Dedicated temperature/humidity sensor with ±0.2°C and ±2% RH accuracy. Lower-power alternative to the BME680 when pressure and air quality are not needed. Current: ~0.5 mA during measurement, <1 µA idle.

### Meshtastic Telemetry on T-Beam / Generic Boards

Meshtastic supports telemetry from I2C sensors wired to the GPIO header of ESP32-based boards. Common pairings include:

- **BMP280 / BME280** - Temperature, pressure, and (BME280) humidity. Widely available and inexpensive. Direct I2C wiring to SDA/SCL pins. The BME280 draws only ~3.6 µA active (typical, @ 1 Hz, humidity+pressure+temperature) and well under 1 µA in sleep per the Bosch datasheet - negligible relative to the radio and MCU.
- **SHT31** - High-accuracy temperature and humidity (±0.3°C, ±2% RH). More robust against contamination than the cheap capacitive temperature/humidity modules often used on hobbyist nodes.
- Enable the Telemetry module in Meshtastic and set the sensor type in the module config. Data is broadcast on the mesh as Protobuf telemetry packets at the configured interval.

### Power Consumption Comparison

<table id="bkmrk-componentactive-curr"> <thead><tr><th>Component</th><th>Active Current</th><th>Sleep Current</th></tr></thead> <tbody> <tr><td>RAK4631 base node (LoRa TX)</td><td>10 - 50 mA (lower-power TX); SX1262 reaches ~118 mA at +22 dBm</td><td>2.5 µA</td></tr> <tr><td>BME680 (RAK1906)</td><td>+microamps (T/RH/P); gas heater several mA in bursts only when enabled</td><td>+0.15 µA</td></tr> <tr><td>SHTC3 (RAK1901)</td><td>+~0.5 mA (during measurement)</td><td>+0.5 µA</td></tr> <tr><td>ZOE-M8Q GPS (RAK12500)</td><td>+~17-18 mA</td><td>+7.5 µA (backup)</td></tr> <tr><td>MQ-2 heater (RAK12004)</td><td>+150 mA</td><td>Cannot sleep heater</td></tr> <tr><td>T-Beam + BME280 (Meshtastic)</td><td>~80 mA (board-level)</td><td>~500 µA</td></tr> </tbody></table>

Note: the T-Beam figures are board-level (ESP32 + GPS + peripherals). Stock T-Beam deep-sleep current is frequently in the low-mA range unless peripherals are disabled, and is often higher than 500 µA in practice; the BME280's own contribution is microamp-level.

For battery-constrained outdoor deployments the RAK WisBlock platform with BME680 or SHTC3 is strongly preferred. Base sleep current below 5 µA enables multi-month operation on a modest LiPo without solar, assuming moderate temperatures - cold significantly reduces usable battery capacity. **Outdoor lithium-powered nodes (including LiFePO4) must not be charged below 0°C (32°F);** see the deployment pages for low-temperature charge-cutoff guidance when a node is solar-equipped.

### Form Factor and Weatherproofing

Outdoor sensor nodes must be rated for the deployment environment. Common IP ratings relevant to mesh sensor nodes:

- **IP65** - Dust-tight, protected against low-pressure water jets. Minimum for exposed outdoor use.
- **IP67** - Dust-tight, temporary immersion to 1 m. Suitable for ground-level or flood-risk sites.
- **IP68** - Continuous submersion rated. Required near water crossings or in humid tropical climates.

Membrane vents (Gore-Tex or equivalent) are essential for enclosures containing humidity sensors. A sealed enclosure traps heat and distorts readings. In the Northern Hemisphere, mount the enclosure on a north-facing surface to minimise solar heating effects on temperature sensors, or use a radiation shield (Stevenson screen style) for meteorological-grade accuracy.