Enclosure Sensor Board

3D Printer Enclosure Sensors & Heater Control

Hardware for closed-loop control of the air temperature inside a 3D printer enclosure. The system pairs a chain of small I²C sensor PCBs with a hacked space-heater whose mechanical thermostat has been replaced by a solid-state relay, all driven from a Raspberry Pi running OctoPrint.

The end result is software-controlled enclosure temperature with multi-point monitoring, which is what made it possible to reliably print materials like polypropylene on a stock Ender 3 V3 SE.

Sensor boards

A small, chainable I²C PCB designed to be daisy-chained around the inside of the enclosure to give multi-point temperature readings.

• MCP9808 high-accuracy digital temperature sensor
• Optional, depopulatable footprint for a BME280 for combined temperature / humidity / pressure
• 4-pin power + bus connector on each end so boards chain in series with no glue logic
• 4-position DIP switch on the back to assign each board's two I²C addresses

No I²C bus repeaters are used. The full chain runs to a Raspberry Pi 4, which tolerates significantly more bus capacitance than the I²C spec calls for -- this lets the design stay cheap and dumb while still working reliably across the full enclosure length.

Two BOM variants are provided in the project:

• Enclosure Sensor Board BOM.csv -- full populate (MCP9808 + BME280)
• Enclosure Sensor Board - T Only BOM.csv -- temperature only (MCP9808, no humidity)

A printable holder for the assembled board is provided in Sensor Board/Enclosure Sensor Holder/ as Inventor source plus exported .stl and .3mf.

Heater control

A space heater modified by removing its bimetal thermostat and substituting an SSR-40DA solid-state relay so that the heater can be switched from a GPIO. The control loop runs on the Pi and uses the sensor chain above for feedback -- a slow PWM (~1–10 Hz) drives the SSR, and the resulting average power maintains a setpoint via a PID loop in OctoPrint.

Heater/ contains:

• SSR Holder/ -- Inventor part + exported .stl / .3mf / .wmv for a bracket that mechanically captures the SSR
• SSR40DA Part/ -- Inventor model of the SSR itself, used while designing the holder
• SSR Data/ -- bench measurements taken while characterising the SSR's switching behaviour at different drive voltages, captured with Digilent WaveForms. The .csv files in this folder are the raw scope captures:
  • 30V Step Test.csv -- turn-on/turn-off response at 30 V load, nominal control drive
  • 30V Step Test 3v3 Drive.csv -- same, but driven directly from a 3.3 V GPIO (the real use case)
  • 120VAC 3v3 Test.csv -- switching behaviour with a 120 VAC load
• Notes.txt -- control-loop notes (PWM frequency target)

License

Released under the MIT License -- see LICENSE.