3D Printer Enclosure Air Quality Monitor with Ventilation Fan Control

Enclosing a 3D printer improves ABS and ASA prints, but it also traps heat and the volatile compounds filaments release — and most hobby enclosures have no instrumentation at all. Users discover overheating when a print warps, and fumes when the room smells. This project instruments the enclosure: a BME280 measures temperature and humidity, an MQ-135 tracks air-quality trends, and an ESP32 runs the control loop — fan on at temperature or air-quality thresholds, thermal alarm with buzzer at the high limit, everything visible on an OLED and a WiFi dashboard. The report documents what each sensor can and cannot claim: the BME280 is a proper calibrated sensor, while the MQ-135 needs a 24-hour burn-in and yields a relative index, not laboratory ppm. That distinction — plus a fan that demonstrably spins up when you warm the sensor or waft a solvent — makes the demo and the viva both credible.

1. The ESP32 samples the BME280 (temperature, humidity) and the MQ-135 (analog air-quality signal) on a fixed cycle (design target ~5 s).
2. The MQ-135 reading is normalized against its burn-in baseline into a relative air-quality index (design target 0–100 scale).
3. Temperature and the index are each compared against their on/off threshold pairs with hysteresis.
4. When either threshold trips, the relay energizes the 12 V fan; the OLED and dashboard switch fan state to ON with the triggering cause.
5. If temperature crosses the separate high-limit, the buzzer sounds and the OLED shows a thermal warning regardless of fan state.
6. When readings fall back below the off-points, the fan stops; all transitions are logged with timestamps on the dashboard.
7. Thresholds are editable on the WiFi page and apply immediately, so examiners can force a fan cycle during the demo.

Tech stack:

• ESP32 (WiFi-enabled microcontroller)
• BME280 temperature/humidity/pressure sensor
• MQ-135 air-quality gas sensor
• 2-channel 5 V relay module
• 12 V DC cooling fan
• 0.96" OLED display (I2C)
• Piezo buzzer
• Arduino IDE · ESP32 core

• [BME280 climate sensing] Temperature (±0.5 °C) and humidity (±3 %RH) from a factory-calibrated sensor — the trustworthy half of the instrument.
• [MQ-135 air-quality trend] Tin-oxide gas sensor tracked as a relative air-quality index after burn-in, used for fan control and alerting, never as certified ppm.
• [Relay fan control] A 2-channel relay drives a 12 V enclosure fan with separate temperature and air-quality thresholds plus hysteresis.
• [Thermal high-limit alarm] Buzzer and OLED warning when temperature crosses the safety limit, independent of the fan loop.
• [OLED live display] Enclosure temperature, humidity, air-quality index and fan state on a 0.96" OLED.
• [WiFi dashboard] The ESP32 hosts a local page with live readings, threshold settings and recent fan/alarm events.
• [Hysteresis control] Separate on/off points per threshold stop the fan from chattering at the boundary — demonstrated live.
• [Burn-in calibration note] A documented MQ-135 burn-in and baseline procedure so the index means something for the buyer's enclosure.

• Fully wired prototype: ESP32 assembly, BME280, MQ-135, relay module, 12 V fan, OLED, buzzer
• Acrylic enclosure corner panel for the demo arrangement
• ESP32 firmware source code with thresholds and hysteresis logic
• MQ-135 burn-in and baseline calibration procedure
• Wiring diagram and connection table
• Project report PDF (background, sensor theory, methodology, results, limitations)
• PPT presentation for final review
• Viva Q&A preparation document (BME280 vs MQ-135 sensing principles, hysteresis, burn-in)

• The MQ-135 yields a relative air-quality index, not certified VOC ppm — the listing never claims laboratory-grade gas measurement, and neither should the student.
• The monitor assists supervision; it does not make an enclosed printer safe to leave unattended — thermal runaway protection remains the printer firmware's job.
• The fan moves air but is not a fume-extraction system; ducting to outdoors is listed as future scope.
• MQ-135 needs the documented burn-in before readings stabilize; first-day numbers are meaningless.
• The demo enclosure corner is a display arrangement, not a full printer enclosure — the buyer mounts sensors in their own enclosure per the guide.