The controller consists of:
- an RPM sensor (an opto emitter and receiver pair) mounted in the router body
- a TRIAC to control the router speed
- a zero cross detector so we can do phase control
- an Arduino to compare the target RPM with the real RPM and make changes using PID
You can order a PCB from osh park, and you'll need components spec'd in the BOM. If you are going to give it a go then let me know because I've made a few changes that haven't been merged into the schematic yet. Check the todo section of the github readme.