ESPHome Sen66 Air Quality Sensor

A new all-in-one sensor from Senserion with a new case for it. This is similar to my Sen55 case (Link, in black, first picture), but smaller. 

A few improvements over the last design:

• Smaller footprint

• Smaller fan

• Easier to print tray

• Better Sensor (now with CO2, etc)

• No fiddly front grill that falls out without glue

BOM

• Printed parts (1x Case, 1x Tray, 1x Sensor clip)

• Senserion Sen6x module (pick based on your preferences)

• JST-GHR-06 cable (like this: Link)

• Any small ESP32, preferably Seeed Studio XIAO ESP32-C3, C6 or S3

• USB-C Charger spoofing board (this will power all components and make sure they get 5V no matter what kind of charger you hook this up to)

• Noctua NF-A4x10 5V PWM (or any other 40mm PWM fan, this is designed for a 10mm deep fan)

• Soldering tools

• A handful of breadboard jumper cables or thin wire (Jumper cables and pins make the ESP32 removable in case it breaks)

• 2x M3 Heat-set Inserts

• 2x M3x8 or M3x10 screws

• Double-sided tape

• A few Zip ties for cable management

• Razor blade to trim printed parts if they don't fit

Printing

Print the Housing face-side down, meaning the cheese grater is on the build plate.

The Tray needs to be printed flat. The cheesegrater pattern in the back might be a tad difficult, but with a bit of tuning it will work. If you print in PETG, make sure to have retraction, cooling and flow configured correctly, or you will end up with holes (see last picture). 

The Sen6x clip should print fine with the clips sticking up. They shouldn't require supports, but use them if it doesn't print for you.

Assembly

Print the parts, remove supports if you used them (the cheese grater pattern might require them). Press the heat-set inserts into the holes at the front for mounting the fan.

Before you assemble everything and glue things down, you should test your electronics. Make sure you can get a reading from the sensor, and that everything works as intended. If you use ESPHome, make sure to install it on the ESP before adding the sensor and the fan, so you can push later updates via OTA updates, instead of having to manually connect it. Having the fan run through the internal power supply can fry the board, since it draws too much current at max speed on some boards. 

When everything is printed and your electronics work, put the Sen6x into its clip, and put it into the tray. If it doesn't stay, use a drop or two of superglue to hold it down. Note the orientation, the two small holes on the sensor should face the ramp pointed at the fan, the fan in the sensor should face the back. 

At this point, solder everything together, ajust cable lengths as needed, or keep them at full length so you don't have to choose (like I did in the pictures). You can use Dupont, Microfit or JST connectors inside to keep things modular, but it might get a bit cramped in the housing. My recommendation is to solder Pins to the ESP board, so you can take it out again, but to solder the power wires to the supply board (This shouldn't break).

Place the USB-C board on the tray, plug it in with the cable running through the shell, to get an estimate for where you have to place it with tape. These boards come in a variety of shapes and sizes, so there's no universal formula for this.

Once your power delivery board is taped down, take a small piece of double sided tape to secure the ESP (if you don't want it floating around). I designed the case so there would be some airflow over the board to keep it cool, in case you want to do other things with this board, not just the Air Sensor part.

Finally, the cables need some tidying up, especially if you kept them long. Everything should be ready to deploy. Slide the tray into the case, and plug it in.

Why a fan?

I've run these sensors for months, and run some very unscientific tests with and without fans in different housings so they don't look awful sitting on my kitchen counter, in my bathroom, or at my desk. One thing is quite clear: Putting this sensor into a housing without some way to push air through it makes them less usable. Readings take (in some cases) more than half an hour to reflect the actual state of the air in the room, compared to just having the sensor and all the wires out in the open. Additionally, a fan keeps the sensor from recycling its own air, which would throw off readings as well.

ESPHome notes

I used uELKO's "External Components" library to make the Sen66 work, since there was no support for it natively at the time. I haven't changed my code since, since everything works just fine this way, but it might be supported natively by the time you read this. I also copied some of their code for the more complex functions that they already figured out (thank you <3).