On Mon, 10 Mar 2008, John Kasunich wrote: > > Kirk Wallace wrote: >> I am looking into adding a knob for setting spindle speed manually. This >> serial encoder is close to what I am looking for: >> >> http://www.usdigital.com/products/a2/ >> >> but is over-kill and way too expensive. Does anyone have a link to an 8 >> or 10 bit serial (SPI like) absolute encoder? I checked Digikey but >> didn't find anything. Other options are to use a potentiometer and >> serial ADC or PWM to serial, but an inexpensive single unit would be >> better. Thanks. > > I would not recommend absolute encoders (or pots with A/Ds, which are > also absolute). > > Think about something like feed override, where the is a slider on the > GUI as well as a physical knob. If you turn the knob, EMC will adjust > the position of the slider to match. But if you move the GUI slider, it > is impossible to turn the knob to match. > > If you use an incremental encoder with no scale, then it can coexist > nicely with the GUI slider (or with other physical controls - for > example you could have a knob at the machine control, and another knob > located on the far side of a large machine table. > > Another example would be on-off controls like spindle or coolant. If > you use a toggle switch, you can have only one. If you use start and > stop buttons, you can have as many of each as you want. > > This concept of using incremental controls is a fundamental principle > adopted by NIST when they were designing EMC. Think long and hard about > the implications before you switch to absolute controls. > > Regards, > > John Kasunich
I agree wholeheartedly with John. However if you do need an inexpensive absolute encoder, austria microsystems makes an interesting magnetic sensor with 8-12 bit precision for under $20: http://www.austriamicrosystems.com/03products/20_rotary_encoders.htm They have the magnets too. -fenn ------------------------------------------------------------------------- This SF.net email is sponsored by: Microsoft Defy all challenges. Microsoft(R) Visual Studio 2008. http://clk.atdmt.com/MRT/go/vse0120000070mrt/direct/01/ _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
