I understand that the current focus is to increase stability, Achim, we hear you! 
I will stay say it, for future reference: the question about the pinouts for shields could be easily solved if the case had a little more space above the D1 (or C3 in the future). Any shield could then go piggyback on top of the D1/C3.
You can select faster shipping options in AliExpress. By default it shows the slowest and cheapest. Click on the shipping options and you can see faster ones.
We will also experiement with the C3 or S2 board as a D1 replacement and I will inform if we get it running.
The new design is already submitted for production but I made a note of better placement for the MCU to allow shields on top in one of the next updates.
We are currently making a sample production with a new version that incorporates the following changes:
- ground plane
- improved tracing
- removed D1 shield
- added capacitors (optional) on 3v3 and 5v
- moved JST plug closer to MCU
- button pulls to ground
- OLED display is on 5v
Many thanks for the feedback, especially @ken830 and @l4ur for reviewing the schematics.
I should receive the new PCB next week for testing and will then give an update.
Could you send updated KiCad files for review?
Here are the new files: https://drive.google.com/file/d/1z6g0-oY6amFZzEOuNfQ8zrduPmo9SX5o/view?usp=share_link
Many thanks for reviewing.
Overall pretty good improvements considering your stated goals for this revision. Removing the shield and moving the PMS connector really eased the layout and made everything nicer.
I can see one small area of improvement. The SDA trace doesn’t need this extra transition to bottom layer if you just route SCL on the other side of it:
Like this:
Something to think about when you get an opportunity for the next batch if you’re already in fab with this version.
Got PCB version 4.1. yesterday and everything seems to work:
The PMS cable length is not ideal:
So we will probably switch to a smaller one with the kit.
I will post updated PCB files once we have these small changes done.
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Yay!
It’s looking great! Getting the OLED off the 3.3V rail is a big deal!
I just ordered the new PCB. Main improvements is the cutout around the WiFi antenna and some minor tracing and label improvements.
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@Achim_AirGradient - when would you anticipate the pcb v4.x selling? I’m looking to purchase a unit and am considering if I should wait or not.
By the way, reading the collaboration on this thread is exciting. Thanks to everyone that’s contributing!
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I expect a test board for v4.2 next week. Then if that works well, we will order higher quantities and put them into the shop but we also need to sell off the old boards first.
I think there is no fundamental issue with the previous PCB versions and most problems that people have @ken830 narrowed down on the software serial library. I have many DIY kits with the previous PCB versions running stable. Anyway, I will keep on putting updates in here about the test results and availability.
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Have you considered adding a cutout under the D1? This comment suggested it would improve wifi signal strength. There might be something to that. The current signal strength seems to be good enough in my setup, but my wifi access point does say the my kitchen AirGradient device’s “experience” is lower than anything else in the house (at 72%).
edit: oh, I just noticed in this comment you did exactly that. Neat!
Understood - thanks for the context!
I received the new version and everything looks good and seems to work:
Here you can see the PCB cutout under the D1 mini antenna:
I will test a few days more and then if all is well publish the new instructions including files.
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What procotol is this latest oard using to talk to the PM sensor? UART, i2c, pwm?
The PM sensor we use can only understand UART (via software serial library on the D1 mini).
Looks cool, thanks! I Found this manual
is it the final version? I want to build myself a new version.
About TVOC. I have not yet deeply studied the instructions, maybe I missed something, I did not find instructions for self-production of the module. Can I buy the sensor myself
for example this: https://aliexpress.ru/item/1005003799982166.html
and build my own module for TVOC?
UPD
I understand, these sensors from ali are already suitable, just needs to look for suitable contacts and resistors.
Yes 4.2 is the latest version.
Please note that if you want to use 3rd party TVOC modules you might need to remove the pull up resistors to make it work.
Thanks for the replies, it’s a pity I can’t order a DIY kit (no shipping to my country).