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IAQ BOX - Low-Power IoT Air Quality Monitor IAQ BOX - Low-Power IoT Air Quality Monitor

IAQ BOX - Low-Power IoT Air Quality Monitor

5 Apr 2022

Overview

IAQ BOX is a low-power IoT device that measures air quality (temperature, humidity, air pressure and VOC level) with a Bosch BME680 sensor. The E-Ink display keeps showing the data without drawing power, while solar charging makes the device fully self-sufficient. It was designed for low-power operation and can be integrated into smart home systems over the ESP-NOW protocol.

Technical implementation

Hardware design

  • Custom PCB: designed in EasyEDA to make the connections simpler and safer:
    • ESP8266 (D1 Mini v4.0): an affordable Wi-Fi module on a carrier shield, which avoids having to solder SMD connectors.
    • HT7833 linear voltage regulator: minimal quiescent current and a low dropout voltage.
    • TP4056 charge controller + DW01A battery protection chip: essential for handling the high-capacity battery pack safely.
    • PH2.0/SH1.0 connectors: reliable connections for the E-Ink display and the sensors.
  • Power system:
    • 4× 18650 Li-ion cells in a 1S4P configuration.
    • 5 V 250 mA solar panel: the largest panel that was practical for charging.
  • 3D-printed enclosure:
    • Wood-filled PLA filament: an enclosure that smells like wood and has a rough texture.
    • Magnetic mounting system: easy assembly and an electrical connection to the solar panel.

Software architecture

  • Power-saving firmware:
    • Deep sleep: the device only syncs on every 6th run, which brings the average current draw down to 2.5 mA.
    • Data kept in RTC memory: readings survive deep sleep, because the RTC memory stays powered.
    • ESP-NOW communication: a power-efficient peer-to-peer link to an IAQ BRIDGE device that acts as a gateway.
  • Cloud integration:
    • Adafruit IO: real-time data visualization and history.
    • MQTT: lightweight IoT messaging.
  • Fault tolerance:
    • Automatic recovery when the connection drops.
    • Sensor diagnostics and error handling.
    • Battery health monitoring based on voltage thresholds.

Key features

  • Power-saving display: a 2.9-inch E-Ink display that shows data without consuming power.
  • Self-sufficient: with enough light, solar charging gives it practically unlimited runtime.
  • Modular design: magnetic mounts and connectors make it easy to swap sensors and displays.
  • Smart home compatible: integrates with Home Assistant and other IoT platforms.
  • Cheap to build: all parts together cost less than 30 000 HUF.

Technologies

  • Embedded systems: ESP8266, FreeRTOS (Arduino Core).
  • Protocols: ESP-NOW, MQTT.
  • Cloud services: Adafruit IO.
  • CAD tools: EasyEDA (PCB design), Fusion 360 (3D modeling), Cura (3D printing).
  • Power management: linear voltage regulators, lithium battery management.
  • Data visualization: E-Ink.

Results

  • First place at SZIIV 2022
  • 9.32 mW average power consumption
  • 225 days of runtime
  • E-Ink display
  • ESP-NOW integration
  • Demo video
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