Review of first PCB design - Single Switch Node with Hylink AC/DC

[Chester]

Good evening!

I have been doing some bits and pieces, built a few temperature sensor nodes that are happily collecting information throughout the house.

I wanted to turn my attention to designing some in-wall modules, as I have a specific light switch for my garage that the builders decided to put in a very odd spot, its on the wall right in the middle of where one of our car bonnets end up, so you have to lean across the car just to turn the lights on!

So this is the first module I have ever designed, its done in EAGLE, with a combination of imported libraries for things like the HLK-PM03, and I have modified a pro-mini 3v3 layout to remove some of the pins that I won't use in this project, to try and keep things a little easier to route.

This is also the first time I have done PCB work with 240V power, so I would appreciate any comments that you might have!

One thing to note is that currently there are just mounting holes for the Live and Neutral inputs, I haven't yet decided on the terminals for those, I'll have to pop down to Jaycar Electronics during the week and pick up some samples for measurement so that I can make a footprint for them. Also, the Serial Upload pins shown in the image are just because I didn't get around to removing them from the design, I would still have them on the end product, but I would spin them around so they run over the top of the pro-mini board.

Many thanks to everyone on the "Safe in wall ac/dc converters" thread, that has been very invaluable for research!

I know that I haven't got any voids in the board to section off the AC traces, that is my next learning experience too

Some things to consider, will be that I will have a capacitive switch sensor for the 3 pin header, I will mount that behind a blank faceplate, and have the LED lighting up the faceplate. Further versions will have more than one switch sensor and LED, this is just to get an idea of size and how well it fits behind a wallplate. I'm also using the HLK PM-03, which gives a 3v3 output, so I don't have to bother with voltage regulation for the RFM69, and the capacitive buttons are happy with a 3v3 input too, with no degradation in range/sensitivity.

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[sundberg84]

@chester Hi!

When i designed my first AC/DC pcb i read alof and tried to collect as much info as possible here: https://forum.mysensors.org/topic/4175/clearance-creepage-and-other-safety-aspects-in-mysensors-pcbs/

There are more to discuss and im not sure everything is 100% but some notes on your design:

I would add a air-gap (drill) here to get more creepage (this it not safe and you have to measure every distance between traces) or move the component to allow more creepange and clearance.

It all depends on in which enviroment you are going to use this but if you design a case (sealed).

"If you seal your box completely (see IP classifications) to avoid contamination from your environment you can design your board with distansens from pollution degree 1. This means pretty much clearance and creepage are the same. This means you need at 250v 0.56 mm [ref] between AC circuit (basic insulation) and 3.3mm between AC high voltage and DC low voltage. This has alot to do with material quality so I would add some extra space to be sure."

Im always using 5mm between AC/DC and 3mm between AC/AC (same as in between the HLK-PM pins).

Check out the design of my HLK-PM01 pcb

https://www.openhardware.io/view/504/HLK-PM01-breakout-board

Edit: Also, increase the drillholes for the varistor and HLK.
They are much bigger in real life.

[Chester]

@sundberg84 Thank you so much for the advice, I knew that it would come down to small things here and there, and it's so much easier to tinker around in eagle than try to order a board, find the errors and fix/reorder over and over, so I appreciate it very much!

Time to get back in and make some changes