I wanted to slow down my Dewalt router to 12000 RPM so I started to investigate a closed loop controller. So I looked into SuperPID which seemed to be what I needed. However at $200 it didn’t seem to be worth it. So I designed my own, most of the parts I had n had to order about $30 of components. I’m using an Arduino Nano to measure speed using an optical sensor and control the router using a triac by changing the firing angles. I had to modify the router to bypass the internal speed controller. Speed set point is received from my GRBL board which is another Arduino Nano. Now I can slow down the router to 5000 RPMs. To view all the information and modify setting I use wifi and app. Just wanted to let people know incase they are looking for the same thing but felt SuperPID is too expensive. I’ll post pics soon.