Dear forum,
I am working on an open source / open hardware project that started out as a remote switch for my coffee machine - hence the name. The initial build was put together on vero board but since this prototype has been running stable without issues for a couple of months now, I want to move on to making a PCB layout and pushing the project to my github for everyone else to fiddle with it. Of course all schematics, KiCAD files, BOM, and firmware will be released under a suitable license. I am thinking MIT license but suggestions are welcome - this is my first contribution to the OSHW world.
The initial design consists of a Wemos D1 mini, one relay, MAX6675 + K-Type TC and a MeanWell IRM board mounted AC/DC 5V converter (Class II) enclosed in an industrial style plastic case.
Now here is my question: With only one Class II isolated power supply on-board, is it of any use to control the relay via an isolated optocoupler?
Mainly, I want to make the design as reliable and safe as possible, but I am not an electrician. What kind of safety features should I look into? Of course mains and low voltage circuits will be separated on the PCB and isolation slots incorporated to work against surface creepage.
Also: This started out as a one-off build for my own purpose, but I thought others might be interested as well. I want to keep the platform as adaptable as possible so I am thankful for any suggestions / wishes of features to build in. All unused pins will be broken out to the edge of the PCB. I also thought about possible solutions for plug-in modules via industrial connectors but have yet to sort out some design decisions.
At the moment, the webserver has the Wifi credentials hard coded into the firmware on upload. However I am working on a new version using a wifi manager and a physical switch to put the ESP into AP mode for configuration. Also firmware update OTA is on the list, but I did not implement it properly as of today.
Here are some logo ideas/sketches you might or might not like, feedback is welcome too
Please let me know what you think and fire away your suggestions.
Thank you!
Frederik
Edit: Fixed broken links.