3D Printer Enclosure Guard: Heat and Fume Monitor with Auto Shut-Off

Enclosures help ABS and ASA prints, but they trap heat and fumes. A BME280 and an SGP30 inside the box report to Home Assistant over MQTT, and an automation switches off the printer's smart plug when temperature or VOC readings cross your limits.

Mission steps

1. Mount the sensors

   Place the BME280 and SGP30 high inside the enclosure, away from the hotend and heated bed, wired to the Pi's I2C pins.

2. Install libraries

   In a venv run pip install adafruit-blinka adafruit-circuitpython-bme280 adafruit-circuitpython-sgp30 paho-mqtt.

3. Publish readings

   The script reads every second (the SGP30 needs that rhythm) and publishes to MQTT; it sends an alarm message over the limits.

4. Add the shut-off

   In Home Assistant, an automation on the alarm topic turns off the printer's smart plug and notifies your phone.

5. Test safely

   Lower the temperature limit below room temperature for a minute and confirm the plug switches off.

Code

import time, json, board
import paho.mqtt.client as mqtt
import adafruit_sgp30
from adafruit_bme280 import basic as adafruit_bme280

i2c = board.I2C()
bme = adafruit_bme280.Adafruit_BME280_I2C(i2c, address=0x76)
sgp = adafruit_sgp30.Adafruit_SGP30(i2c)
sgp.iaq_init()

client = mqtt.Client(mqtt.CallbackAPIVersion.VERSION2)
client.username_pw_set('printer', 'change-me')
client.connect('homeassistant.local', 1883)
client.loop_start()

MAX_C, MAX_TVOC = 55, 2000          # tune for your printer and filament
while True:
    t, tvoc = bme.temperature, sgp.TVOC
    client.publish('enclosure/state', json.dumps({'temp': round(t, 1), 'tvoc': tvoc}))
    if t > MAX_C or tvoc > MAX_TVOC:
        client.publish('enclosure/alarm', 'ON')
    time.sleep(1)

alias: Printer enclosure emergency off
triggers:
  - trigger: mqtt
    topic: enclosure/alarm
    payload: "ON"
actions:
  - action: switch.turn_off
    target:
      entity_id: switch.printer_plug
  - action: notify.notify
    data:
      message: "Printer power cut: enclosure too hot or fumes too high."
mode: single

Tip: test every script on the bench before installing it in a moving machine.

Questions