I have a nice home brew table top mill that I am currently retrofitting. I would like to be able to know how fast my spindle is turning so I can use speed and feed calcs. Do they make something I can use that will attach to my spindle and tell me it’s RPM? I have a NI DAQ card that I can use to display this information on the PC I am using if had some kind of output voltage or something and know how that voltage relates to RPM.