DIY Home Lab Sensors — Temp, Motion & CO2 Projects

Connectivity & data flow

• MQTT → Home Assistant dashboard
  • MQTT is lightweight and widely supported. Sensors publish to an MQTT broker and Home Assistant subscribes to topics to display data and trigger automations.
• HTTP/REST → Graylog ingestion for logs/alerts
  • Use HTTP POST to forward sensor events into a centralized log collector like Graylog for long-term storage, search, and alerting.
• Hybrid setups
  • Use ESP32 nodes to publish via MQTT to a Raspberry Pi gateway that forwards selected events to Graylog or stores them locally.

Design considerations

• Keep message formats simple and consistent across sensors.
• Use retained messages for last-known-state where appropriate.
• Implement local buffering when network connectivity is intermittent.

Project walkthroughs

Temp + humidity monitor (ESP32 + BME280)

• Concept: Networked temperature and humidity nodes to monitor server racks and cabinets.
• Parts: ESP32 dev board; BME280 sensor module; JST connector and small enclosure; Power supply (USB or LiPo for battery).
• Wiring notes: Connect BME280 via I2C (SDA, SCL, 3.3V, GND). Use pull-ups if your module lacks them.
• Integration: Publish sensor readings to an MQTT broker; create sensors in Home Assistant to visualize and alert on thresholds (over-temperature or high humidity).
• Practical tip: Place sensors near hotspots (air intakes, rack top) and avoid direct airflow from fans to prevent misleading readings.

Smart CO2 monitor (Sensirion SCD4x + ESP32)

• Concept: Reliable CO2 monitoring for room ventilation and air quality alerts.
• Parts: ESP32 dev board; Sensirion SCD4x breakout (factory-calibrated CO2, temperature, humidity); Enclosure with airflow paths.
• Wiring notes: Connect via I2C or the recommended interface on the breakout. Ensure proper 3.3V logic compatibility.
• Integration: Report CO2 ppm to Home Assistant and use automations for ventilation or notifications when values exceed comfort thresholds.
• Practical tip: Allow a stabilization period after powering the sensor; follow manufacturer guidance for calibration intervals.

PIR security alarm (Raspberry Pi + PIR sensor)

• Concept: Detect unexpected motion in sensitive areas and send notifications.
• Parts: Raspberry Pi (any model with GPIO); HC-SR501 or similar PIR sensor; Optional buzzer or relay for local alarm.
• Wiring notes: Connect PIR VCC to 5V or 3.3V as appropriate, GND to ground, and output to a GPIO pin with pull-down logic.
• Integration: Raspberry Pi can send events via MQTT to Home Assistant or call a webhook that records events to Graylog for audit trails.
• Practical tip: Tune PIR sensitivity and timeout to reduce false positives from HVAC or pets.

Centralized logging (Graylog for IoT sensor data)

• Concept: Aggregate telemetry and historical logs for analysis and alerts.
• Setup notes: Configure a Graylog input to accept JSON-formatted HTTP events or ingest via MQTT-to-HTTP bridge. Tag sensor events by location and device type for easier querying.
• Benefits: Long-term retention, structured queries, dashboards, and alerting for anomalous trends or downtime.

Parts list & deployment checklist

General parts for the projects above

• ESP32 dev board (WROOM-based)
• Raspberry Pi (3B/4) for gateway/logger
• BME280 or SHT3x temp/humidity sensors
• Sensirion SCD4x CO2 module
• HC-SR501 PIR motion sensor
• Enclosures, JST connectors, Dupont wires
• Stable power supplies and optional UPS for Raspberry Pi

Deployment checklist

• Verify sensor voltages and logic levels before connecting.
• Test connectivity locally before deploying to remote locations.
• Label devices with unique names and physical locations.
• Document MQTT topics and Graylog fields for each sensor type.

Best practices

• Calibration: Periodically verify sensors against a reference and record drift history. CO2 and humidity sensors can require occasional recalibration or replacement.
• Placement: Avoid direct fan exhausts and place sensors at appropriate heights for the data you want (CO2 near breathing height; temperature sensors where heat accumulates).
• Power management: For battery nodes, use deep sleep modes on ESP32 and sample infrequently for non-critical sensors.
• Security: Use strong authentication for MQTT brokers and TLS where possible. Limit API exposure for Home Assistant and Graylog to your local network or VPN.
• Naming & metadata: Include location, device type, and installation date in telemetry to simplify later analysis.

Privacy & alternatives

DIY sensors are flexible but can raise privacy concerns if you add cameras or audio. Camera-free, anonymous occupancy sensing is a strong alternative when privacy matters.

Butlr offers heat-based, anonymous occupancy sensing that detects presence and movement without capturing images or personal data. It’s a commercial option for people or organizations that want maintenance-free, privacy-first occupancy analytics.

Comparison highlights (DIY vs commercial heat-based)

• DIY sensors:
  • Pros: Low cost, highly customizable, great for hobbyists.
  • Cons: Ongoing maintenance, calibration needs, potential privacy temptations (cameras).
• Commercial heat-based (e.g., Butlr):
  • Pros: Anonymous occupancy detection, enterprise-grade reliability, less maintenance.
  • Cons: Higher upfront cost and less component-level control.

Resources & further reading

• Home Assistant documentation for MQTT sensors and dashboards.
• Graylog guides for ingesting and querying IoT telemetry.
• Sensirion SCD4x technical documentation for CO2 sensor characteristics.
• Community forums and Reddit homelab threads for practical anecdotes and troubleshooting.

FAQ

• Which sensor is best for server racks?
  • Use a temperature-focused sensor like BME280 for ambient readings and consider additional sensors at the intake and exhaust to measure differential temperatures.
• Which sensor should I use for air quality monitoring?
  • CO2 (SCD4x) is a practical proxy for ventilation and occupancy. For particulate matter, consider dedicated PM2.5 sensors if you need particulate monitoring.
• How do I log long-term sensor data?
  • Use a centralized system like Graylog or InfluxDB to store time-series and logs. Retain metadata (device, location) and implement rollups or retention policies to control storage costs.
• Where can I find parts, wiring diagrams, and example code?
  • Many community repositories and vendor guides provide wiring diagrams and code for ESP32/Raspberry Pi sensor integrations. For a polished, privacy-first occupancy alternative, evaluate enterprise heat-based sensors from companies like Butlr.

Next steps

• Build one temp/humidity node and connect it to an MQTT broker to learn the workflow.
• Add a CO2 sensor for air quality and set up a simple Home Assistant automation to alert on high CO2.
• Centralize logs into Graylog for searchable history and alerting.
• If privacy or maintenance is a concern, consider a commercial heat-based occupancy solution for anonymous presence detection.

Download a parts checklist and sample device naming convention to accelerate your deployment and keep your homelab reliable and secure.