On Tuesday 10 November 2009, Pat Lyons wrote: >my photo attachment of the red slide unit was rejected cause it was too big >a file. > >I have a new question though- > >is it possible that these encoders can be counted on both the rising and >falling edge of both signals? >in other words: > >if I count the falling edges on one wire as *640 falling edges per inch*, >does this actually mean its *640 x 2* for rising and falling edges? then x2 >again for two signal quadrature? or is the quadrature pair only to provide >direction information? > >thanks! >-pat
Pat: There are logic diagrams extant here on the web, check the major chip makers sites for application notes (and the wiki.linuxcnc.org pages too) and even complete chips available today that can derive from those quadrature outputs, a complete, valid # of steps and instant direction from them. The only use for the index pulse is so that the count can be zeroed at a specific point in the rotation. And in order for this to not have a potential of a one or two count ambiguity is if the index pulse is narrower than a single edge count going either way, eg the index must be narrow enough, and well centered in the time frame where both A&B are high or both A&B are low. Either that, which requires some decent precision in making the encoder, or a method worked out in the logic so that it will only use one edge of the index pulse, and which edge corresponds to the instant state of the direction signal. I haven't worked out that bit of logic but I believe it could be done. And it would certainly present the least restrictions on how sloppily the encoder is made. Thinking about the index 'problem', it might be possible to use the index pulse edge detected by the correct edge via using the instant direction state to select which edge of the index was actually the correct one. Here are 2 chips that might be usable: <http://www.avagotech.com/docs/AV02-0096EN> And also Pico Systems (our own Jon Elson) makes a board that can apparently handle 4 encoders, but I wasn't able to make the web page show me much about it. It does 24 bit counting. Other choices are just a google away. -- Cheers, Gene "There are four boxes to be used in defense of liberty: soap, ballot, jury, and ammo. Please use in that order." -Ed Howdershelt (Author) The NRA is offering FREE Associate memberships to anyone who wants them. <https://www.nrahq.org/nrabonus/accept-membership.asp> We will have solar energy as soon as the utility companies solve one technical problem -- how to run a sunbeam through a meter. ------------------------------------------------------------------------------ Let Crystal Reports handle the reporting - Free Crystal Reports 2008 30-Day trial. Simplify your report design, integration and deployment - and focus on what you do best, core application coding. Discover what's new with Crystal Reports now. http://p.sf.net/sfu/bobj-july _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
