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Exhaust Fan Controller for Range Hood

Automate your existing range hood exhaust fan, ramping the fan up as-needed based on both temperature above the range and smoke levels.

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While watching our roommate and my wife cooking, I noticed that they frequently didn’t think to turn on the exhaust fan until the kitchen started getting fairly smoky or hot (in the summer). The particular model of range hood we have (IKEA LUFTIG, however when I purchased it I noticed that nearly every major brand had the EXACT same looking model within a few dollars of each other) has 4 buttons (light, fan on/low, fan medium, fan high). Seemed like a very straight-forward fix via a microcontroller, some sensors and relays. I’m partial to Particle Photons and they happen to make a Particle Relay Shield that has 4 relays built-on, so it was a perfect fit. The temp sensor was an easy solution, however smoke proved harder than initially expected.

Sources:
blog.dzl.dk/2012/01/02/hacked-smoke-detector/
Dzl

I started with a MQ-2 gas sensor as it seemed to be what I was after (multiple sources I found referenced using it for detecting smoke). While it technically worked, the readings it gave tended to drift quite a bit (it frequently would start giving readings indicative of a lot of smoke for no particular reason) and of particular issue was the fact that it was sensitive to specific gases in addition to smoke. Of particular interest was LPG, which happens to be the propellant for the cooking spray I frequently used. This would result in the fan ramping to high every time I used the spray, even if I was quite a distance away.

After having disabled the smoke sensor and only using the temperature sensor (which didn’t prove to be enough of an indicator by itself), I finally stumbled upon Dzl’s post in regards to getting analog smoke readings from most any residential smoke alarm. I ultimately bought one (~$10) at the local hardware store and after some time carefully taking it apart (mine had more electrical components hiding the chip than his did) was able to get to the chip and solder a wire to the pin he referred to. After wiring up the power wires to run off of the 5V from the Particle Photon, and cutting the wires to the buzzer I was able to get the analog readings without any issues.

After some initial calibration in my garage I was able to get some rough values. I subsequently soldered everything up and 3D-printed some enclosures for both the Particle Photon Relay Shield and my Sensors. I ran one test seasoning a cast-iron pan to generate smoke and have been happy with the calibration values I arrived at, although I may tweak it over time if warranted.

Exhaust Hood Controller Boxes.f3d

The original Fusion 360 File I used

fusion - 5.08 MB - 07/17/2019 at 17:03

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Exhaust Hood Controller Boxes.step

A STEP version of the project

step - 5.92 MB - 07/17/2019 at 17:03

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Enclosure.stl

Enclosure STL File

Standard Tesselated Geometry - 3.98 MB - 07/17/2019 at 17:03

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Lid.stl

Enclosure Lid STL File

Standard Tesselated Geometry - 29.57 kB - 07/17/2019 at 17:03

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Sensor Enclosure.stl

Sensor Enclosure STL File

Standard Tesselated Geometry - 204.28 kB - 07/17/2019 at 17:03

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View all 6 files

  • 1 × Particle Photon
  • 1 × Particle Relay Shield
  • 1 × 3D-Printed Component: Main Enclosure Lid
  • 1 × 3D-Printed Component: Sensor Enclosure very custom to my specific smoke alarm circuit board, so this may not work with yours.
  • 1 × 3D-Printed Component: Sensor Enclosure Lid

View all 13 components

  • Project Update

    Ben Brooks11/13/2019 at 17:44 0 comments

    Been using this project in it's current configuration for ~6 months now without any issues. Definitely had some concern that there would be drift or complete failure of the smoke detector sensor due to the high-grease environment, but nothing yet. I haven't even needed to adjust my parameters for controlling the fan based on temperature or smoke levels, which was surprising.

    Been one of those rare projects where it just works! I've been very happy with the responsiveness whenever any cooking begins, it's ramp-up as conditions worsen and with how long it runs after cooking stops. An absolute improvement over manual control of the exhaust fan.

View project log

  • 1
    WARNING!

    The first thing you need to know is this is dangerous; proceed at your own risk. The fan is directly wired to 120V and you will be working with this, so be careful and flip the breaker that it is on while you work. If you aren’t comfortable or qualified to work on line voltage, don’t.

  • 2
    Identify your setup

    With that out of the way, proceed with identifying how your fan is controlled using a multi-meter. In my case, power is ran through the switches and toggling them simply completes various circuits (the circuits ultimately being the various windings in the motor allowing it to be multi-speed). The actual wires were connected to the switch terminals with spade connectors, so it was quite easy to unplug them (remembering which wires go where). Ultimately, I bought similar connectors (though not quite the same size) at a local hardware store and crimped these to a piece of copper wire for connection to the relays (taking care to use heat shrink tubing to ensure nothing jostles loose). I then connected another set of wires to the buttons using the bought connectors as well. Additionally, I had to splice off the common wire so that each relay could be connected to it (as evidence by the red twist-on wire connector).

  • 3
    Make the board

    Beyond printing the components, the only other time-consuming part is soldering up the board. My skills are less-than-great and I didn’t run into any issues. While not the prettiest thing I’ve made, just follow the wiring diagram I made below.

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