# Field Sensor Deployment Guide ## Site Selection Place sensors where you need data - not where it is convenient to access. Ideal sites are often inconvenient: a peak for a weather station, a stream bank for water level, a crop row for soil temperature. Choose the site first, then engineer the power and connectivity to support it. ## Weatherproofing Sensors Temperature and humidity sensors require a **radiation shield** (white louvered housing) for accurate readings. In direct sunlight a bare sensor's error can exceed 10 °C, sometimes much more, depending on wind and the sensor (see weather-station siting references). Heat trapped inside a sealed enclosure will do the same. Rules: - Never seal a BME280 or BME680 inside a closed waterproof enclosure - humidity will read 100 % and temperature will reflect enclosure heat, not ambient air. - Mount the sensor in a louvered radiation shield. A hobby plastic louvered shield runs roughly $10-25 (price varies; check a current product listing), while a full traditional Stevenson screen is considerably more expensive. - If you cannot use a radiation shield, at minimum shade the sensor from direct sun and allow free airflow. ## Enclosure Strategy Keep electronics and sensors in separate compartments: - Main board, battery, and solar charge controller in an **IP67 sealed enclosure** (ABS or polycarbonate, UV-rated). - Run sensor wiring through a cable gland or a small hole sealed with self-amalgamating tape. - BME280 / BME680: mount in the radiation shield outside the enclosure and run I2C wiring inside. Keep I2C cable runs short - under ~50 cm is a useful rule of thumb, ultimately governed by the 400 pF total bus-capacitance limit in the I2C specification (NXP UM10204). For longer runs use an active I2C bus extender/repeater rather than a simple buffer. - For insect protection, cover any ventilation holes with fine stainless mesh - spiders love warm enclosures. ## Power Sizing Sensor node consumption is low with the right hardware and firmware. The figures below are an idealized best case (they exclude regulator quiescent draw and wake/active current); real nodes often run somewhat higher:
Component Average current (10-min TX interval)
nRF52840 MCU (sleep)~2 µA
BME280 (sleep / active)~0.1 µA sleep; ~3.6 µA active at 1 Hz
LoRa TX burst (10 s/day total)~0.1 mA averaged (TX current × airtime ÷ 86400 s; e.g. ~118 mA at +22 dBm × ~10 s/day ÷ 86400 s ≈ 0.014 mA — adjust for your actual TX power and airtime)
**Total daily****< 5 mAh/day (idealized best case; excludes regulator quiescent and wake/active current)**
- **Battery-only:** 3 000 mAh LiPo → ~600 days as a theoretical maximum. Derate for LiPo self-discharge and regulator quiescent draw - real runtime will be shorter. - **Solar-maintained:** a 1 W (6 V) panel can keep a 3 000 mAh pack topped up at sites that reliably get ~4+ peak-sun-hours, but this does **not** hold in every climate - high-latitude winters and shaded/canopy sites can fall short for extended periods. Size conservatively for worst-case winter insolation rather than assuming indefinite operation. Also ensure the battery is not charged below 0 °C: use a charge controller with a low-temperature charge cutoff (charging any lithium cell, including LiFePO4, below freezing causes plating and permanent damage). - For critical sensors in low-light environments (north-facing, dense canopy), upsize to 2 - 3 W and add a 5 000 - 6 000 mAh pack. Tie panel/battery sizing to your actual load budget and local peak-sun-hours (e.g. via PVWatts/ NREL insolation data) rather than fixed numbers. ## Connectivity Range Sensor nodes use the same LoRa mesh relay infrastructure as every other node. A sensor 20 km from the nearest internet gateway can deliver data with low latency when the relay path is healthy, but mesh delivery is best-effort: expect dropped readings and gaps whenever any hop fails (see Data Gaps below). Do not rely on near-real-time delivery for time-critical or safety-of-life monitoring. When planning a sensor deployment, map out the relay chain first: 1. Identify the target sensor location. 2. Verify line-of-sight or near-LOS to at least one repeater. 3. Trace that repeater's path to a node with internet/MQTT uplink. 4. Add intermediate repeaters if any hop is marginal. ## Data Gaps and Local Storage If the mesh path to a gateway is down, sensor readings are lost - sensor nodes have no local storage. Mitigation options: - **Store-and-Forward (Meshtastic):** the Store & Forward module requires a dedicated ESP32 node with PSRAM acting as a S&F server on a private channel, and it primarily re-serves *text-message* history on request. It is **not** a transparent telemetry buffer that automatically backfills sensor data across gateway outages. For sensor-data gap recovery, prefer local SD logging (below). - **MeshCore room servers:** a Room Server is a store-and-forward BBS that holds room *chat* history for clients on request - it is not a sensor-telemetry buffer that flushes accumulated readings across a gateway outage. See MeshCore docs; do not rely on it to recover lost telemetry. - **Local SD card logging:** for critical sensors add an SD card module and log locally in CSV format. This is the recommended way to recover from gateway outages. A recovery script can push historical data to InfluxDB when connectivity is restored. ## Maintenance Planning Remote sensor nodes require infrequent but non-zero maintenance: - BME280 radiation shield accumulates dust, pollen, and spider webs over time - clean annually or after wildfire smoke events. - **Fit an in-line fuse (or PTC/polyfuse) on the battery positive lead of every field node.** Outdoor wiring is exposed to corrosion, abrasion, and water, and an unfused lithium pack can start a fire on a short. Inspect the fuse and connections during the annual maintenance visit. - INA219 shunt connections can corrode in marine environments - inspect annually and apply dielectric grease. - Battery capacity degrades over 2 - 4 years - plan for a pack swap. - **Label every enclosure** with the node name, deployment date, battery install date, and a contact name/number. Future you (or a search and rescue volunteer) will be grateful. - Design for access: if a node is on a 3-hour hike, make the enclosure tool-free to open (quarter-turn latches rather than screws).