This module uses G6K-2P relays - and its design is inspired by Everlanders Automation projects (video) (Project Home page), where a Wemos D1 min wireless remote control option is added to the MaxxFan in the Everlander rig.
In their project G6L-1P relays are used, but they seem to be more expensive than G6K-2P relays, so this PCB is designed for G6K-2P 5V relays.
(See this MaxxFan Module B page if you want to use G6L-1P relays).
Project Status: PCB design verify (rev.A1 - 2023 May 16)
Here are some screen shots:
Notes about un-knowns:
Use the PCB viewer if you would like to see/test the entire copper path as it switches sides and/or connects to several solder points.
Chips:
Miniature relay G6K-2P
Datasheet: omron_g6k-2-relay.pdf
ULN2803a Darlington Transistor Array
(Top View)
Datasheet: uln2803a.pdf