Bubble counter for monitoring fermentation process. I cracked open one of these (IR Optocoupler LM393) to make them wider. Also you need to have some kind of bubble cap (eg. this one) Afterwards just place it in this rig connect to esp8266 and you should be ready to go. If anyone interested I can share code.
Idea came from this guy. Its modelled in onshape, here is the source.
The author marked this model as their own original creation.