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4 layer PCB version as alternative for coating #74
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I decided to proceed by making a 4 layer PCB layout myself.
Here's a kicad render of the top and bottom sides: I just ordered the board at JLC. I will post back here when I have done some testing with the boards. In case someone else wants to build this, I created a fork with my changes in: https://github.com/nielsfaber/b-parasite |
Hey @nielsfaber tks for sharing! I am happy link your variant in the wiki, but I would suggest we keep your fork separate for now. Otherwise it gets tricky for us to maintain all of them with different calibrations / peripherals (we also have a mini variant in #69 for example). A few thoughts:
I've started working on a v2.0.0 hardware revision with some improvements (revised capacitance sensing circuitry, a couple of buttons, better footprints for hand soldering the RF module). I also fixed the bottom footprint issue you raised in #75. It's a WIP in the Let us know how it goes! |
I agree. Perhaps (in time) it would be nice to add some sort of table with all the flavours such that users can choose.
I work in a company that manufactures electronics boards, we apply conformal coating to boards which need IP67+ rating, but the sides are always left uncoated. I have never heard about cases where moisture creeps in between the layers.
Good point, I didn't consider this at all.
Fair point.
Definitely true, I was planning to make an adapted version (also for reaching the button) when the boards are here.
I will take a look into the revised sensing circuit, thanks for the heads-up. I was wondering whether the Cpara cap needs to be assembled or not (in the current HW revision). Any thoughts on this? |
That's cool! Can I ask you what kind of coating do you use? I only have real experience with acrylic-based ones, but I think there's better stuff out there.
No, it does not. I put the Cpara para there to make probing with the scope easier, but the pads are just connected to the parasitic capacitor in the PCB. It's not a very good idea, and at least I should have marked it as "do not populate" in KiCad. In |
One of the coatings we use is Peters Elpeguard SL 1307 FLZ (link).
Good to know! It was not that evident to me, especially since it was linked with a LCSC part and indeed not marked as not assembled part. Will just remove it when the boards arrive, no problem. |
I hope this is an appropriate place to post this. It occurred to me that relatively inexpensive UV resin for 3d printing would be an excellent way of coating the entire PCB in a durable material. Using a "dunk and cure" approach with multiple layers would make for an extremely rugged surface coating. I don't know why I didn't consider to do this sooner. Has anyone else tried this? |
Hi together, @nielsfaber Thanks! |
@Steiniken
* I still have to decide whether to use the BLE or zigbee firmware version. I haven't found any time yet for any of these. Will follow-up when there is progress on this (I'm also planning to update my forked repo with the changes). |
Hi @nielsfaber |
@Steiniken I put the project on hold since I couldn't get the debugging / programming working. |
Hm, do you think a J-Link helps with troubleshooting? |
According to@nielsfaber
But judging from the picture of the oxidation situation in the wiki, the oxidation starts from the edge. Maybe you can adjust the edges of the copper zones. Keep it away from the cut edge so that the copper will not be exposed to air and water. See how another project handles this https://github.com/diyruz/flower |
I'm very interested in this project.
I have a couple of MiFlora's, but they have not proven to be reliable for me, so I'd like to try a different approach.
I was wondering if any considerations or attempts have been made to use a 4 layer PCB instead.
This would allow the copper pads for moisture measurement to be placed on the inner layers of the PCB, sandwiched between (bare) FR4.
To me it seems more elegant and reliable option compared to using a coating spray, by mitigating the risk for corrosion.
Of course the PCB will become a bit more expensive, but I think the benefits outweigh this.
One concern I have is whether the measurement would be impacted by a change in the PCB layout.
The capacitive coupling to the soil would become slightly different.
Would there be any way to (re)calibrate such PCB layout to obtain the same performance as the original design?
Note: a similar approach can be found here: https://github.com/diyruz/flower
EDIT: I found some pointers on how to re-do the calibration for a different PCB layout.
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