Brushless DC motor diver
    
    Might be needed if I intend to finish a complete CNC mill in Fab Academy. The course requirements are "no commersial boards" so I can't buy a ESC (electronic speed controller) of the shelf.
    
    
    Googling DIY or Open BLDC ESC 2016 to get modern hits
    Resources:
    https://github.com/bluerobotics/BlueESC - last update 2015
    http://diydrones.com/forum/topics/worlds-best-esc-making-it-better - A god reference ESC apparently
    
    VESC
    https://github.com/vedderb - the Repo
    http://vedder.se/2015/01/vesc-open-source-esc/ - The blog / forum /info 
    http://hackaday.com/2016/02/04/adding-position-control-to-an-open-source-brushless-motor-driver/ - Seems like it has position awareness, RPM, current?
    https://www.youtube.com/watch?v=8CcqD5sw90U - Same video if it dies
    Quite possibly overly complicated
    
    
Research for Spindle driver with RPM and current feedback 
RPM reader for off shelf esc:
Resources: Old post about just adding RPM to off shelf esc https://www.rcgroups.com/forums/showthread.php?1006124-Brushless-rpm-Sensor
            Possible component! Does the trick? http://www.onsemi.com/pub_link/Collateral/MC33039-D.PDF
            Fits this controller http://www.onsemi.com/pub_link/Collateral/MC33035-D.PDF
            Together: http://www.onsemi.com/pub_link/Collateral/AN1046-D.PDF
            People using them: https://www.youtube.com/watch?v=Oz59tlRYJi8
                            MC33035 and MC33039 on breakboard, Mosfet IFR3205 and fet driver on testboard. yes i have been modified the schematic in MC33035 datasheet.
            Above uses hall effect sensors. 3 off.
            
            RPM Reader that you can stick on a BLDC
            https://www.eagletreesystems.com/Manuals/brushless-rpm.pdf
            People discussing it:
            http://diydrones.com/forum/topics/brushless-motor-rpm-sensor?id=705844%3ATopic%3A86002&page=3#comments

    another RPM ESC sensor
    http://www.robotshop.com/en/brushless-motor-rpm-sensor-v2.html Or rather the same from eagle tree....


Should be simple!! Just look at the scope. 
https://www.youtube.com/watch?v=-W9ocPHoNNY
Filter and compensate for coils and done... Or hack the esc to output it.
For detectinga a specific frequency: http://www.instructables.com/id/Frequency-Detector-using-PIC-12F683-Processor/
For more frequencies:  http://www.instructables.com/id/Arduino-Frequency-Counter/
                    http://circuitdigest.com/microcontroller-projects/arduino-frequency-counter-circuit



Simplest seems to make something like the blueesc and output digitally.
https://github.com/bluerobotics/BlueESC
Or buy and hack these or simmilar: https://hobbyking.com/en_us/multi-rotors-drones-parts-1/speed-controller-esc-1/afro-esc-series.html they are a predecessor

Seems easiest to hack firmware of an existing?

MAX EASY:
Hall sensor + magnet / optocounter Attach were you want, ex on stepper. Integrate into stepper driver board