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--- construction [2024/04/26 00:12] – [Removal] river
+++ construction [2024/04/28 01:51] (current) – river
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 ====== Electronics Construction / Hardware Notes ======
-===== Conformal Coating =====
+Excellent looking guide to waterproofing electronics, from people who have done it for underwater sensors: [[https://thecavepearlproject.org/2023/03/17/waterproofing-your-electronics-project/|Waterproofing electronics]].
-This is a very worthwhile technique to protect any electronics that has a chance of getting wet. I have spent weeks repairing electronics that was damaged by water, which would probably have been fine if the manufacturer had spent a little more time on coating the PCBs. Enclosures designed to be waterproof often end up not being so.
+[[conformal_coating|Conformal Coating]]
-The types of most relevance for most things are probably acrylic or silicone. Acrylic generally and silicone if needed for higher temperatures or some chemical resistance. Other types are more resistant to chemicals and heat but probably more expensive and/or harder to use.
+===== Waterproof Enclosures =====
-Application in small quantities will probably be by brush or spray. A spray can is much quicker and easier unless you have a lot of parts to mask, then maybe quicker to brush around them. Note though that the coating will spread out somewhat and may be drawn into unmasked parts.
+==== Metal or plastic? ====
-==== Parts to mask ====
+Metal can corrode, but provides RF screening, and may be stronger if it could get bashed. RF screening is generally good, especially when you are putting it beside other radios up a mast, but bad if you want to talk to small WiFi boards that are inside it. :) Also not suitable for putting a lightning detector inside.
-  * Moving parts: buttons, encoders.
+=== HAMMOND 1590WPFL ===
-  * Connectors. Put the mating parts together first too.
-  * Test points and programming pads if still needed.
-  * Antennas or other areas sensitive to dielectric constant. (Unless you design with coating in mind of course).
-  * Sensor holes - like barometers and humidity sensors.
-Parts not conformal coated may be suitable to be protected with silicone grease - particularly connectors.
+{{:ribbed_hammond_box.jpg?600|}}
-==== Removal ====
+This is a HAMMOND 1590WPFL, which I got to try.
-Acrylic softens in IPA. I read on a forum that tetrahydrofuran (THF) would work much better, but I've not tried it. Supposedly acetone works but might damage the board.
+I did not consider when ordering this box that it has internal ribs. This is a problem for forming a watertight seal with connectors that want to do that on the inside. I ground an area flat around the hole for the NMEA-2000 connector, and applied plenty of butyl sealant tape.
-Acrylic and silicone can also be burnt off with a soldering iron.
+The N type connector in the foreground is designed to seal on the outside. I choose this because it seemed like a better idea. This kind is harder to find. I thought the sealing o-ring was barely thick enough though, so I added butyl here too.
-I have found that I can use multimeter probes on acrylic coated parts without removing the coating - it seems the probes can just push through, but not super reliably.
+This box type is also not that great, because the seal is a stick on rubber gasket that goes on the edge, without any flange.  It looks like a box that was not designed to be waterproof, but the seal was an add-on. I'd get something better next time.
-==== Hacky Options ====
+I also noticed now that the picture on Farnell is wrong. The datasheet is correct though.
-Acrylic conformal coating looks, feels, and smells very much like clear nail varnish. I don't know if they are any different.
+It comes with zinc plated screws and rubber o-rings for them. This is not ideal - both because the screws will probably corrode themselves in salt water, and because of galvanic corrosion with the aluminium box. Marine stainless screws with a suitable compound would be much better.
-Other grease coatings. Lanocoat if that's what you have on hand?
+Another detail is that the box is thinner at the bottom, which you need to allow for if measuring. Maybe better to design inserts / PCBs to the datasheet spec.
-==== Questions ====
+=== A Plastic Box ===
-How much does coating affect frequency of crystal oscillators? They are easily pulled by changes in capacitance.
+{{::img_20240428_023639.jpg?600|}}
-===== Links =====
+I also have a plastic box. It seems to be meant as a junction box, and has knockouts on the sides. These are far too large to be useful for my purposes, so they will just weaken the box. It has plastic fasteners to hold the lid on, which is good for corrosion, but no way to mount it without drilling a hole to the inside, or glueing something on. Some boxes like this do have a place to put mounting screws under the box fasteners, but this one doesn't.
-  * Excellent looking guide to waterproofing electronics, from people who have done it for underwater sensors: [[https://thecavepearlproject.org/2023/03/17/waterproofing-your-electronics-project/|Waterproofing electronics]].
-  * [[https://titoma.com/blog/conformal-coating|A good guide to conformal coating]]