On Thursday 20 April 2017 23:54:53 Danny Miller wrote: > Leadshine drives input/output are not just opto, they're differential. > i.e. the step signal has 2 wires and dir has 2 wires, there's no > common ground or common anode. So they're not just galvoisolated from > the pulse source, but from each other. > > When run as twisted pairs or just pairs, the noise immunity is greater > than you'd ever need. > > You are still going to tie them together as common-gnd or common-anode > at the pulse source, but the differential-pair part that creates is > important.
You are saying in essence that I should be powering the drivers opto's as two twisted pairs, + from the 5 volt source on the 7i90, and - from the gpio pin. Nice in theory I suppose, but prevented by the fact that the 7i90 has a total of 4, 5 volt srcs, one pin on each of the 3 50 pin connectors and the 5 volt power src. The ability to handle large numbers of 5 volt srcs is handled by an inch of bare 14 gauge wire inserted into the back of that teeny power connector, and the various grounds and 5 volt loads such as the + connectors on the drives are soldered on there. Grounds can be had as there is a ground pin on the other row of the 50 pin for every active input or output. Radiated noise inside the box those 2 drivers are in can be picked up with nothing but the push-on clip it to a wire clip of the typical 10x probe feeding a gigahertz sampler scope, spectrum of that noise seems peaked at 90 to 110 mhz, and can easily exceed 30 volts peak to peak in the air 2" from the drivers. With only a 5 volt tolerance at the connections on the 7i90, I've destroyed 3 of the 7i90's so far. I see that going to fiber as a way to prevent the nominally 12" piece of ribbon cable going to the drivers input opto's as an antenna, potentially destroying yet another 7i90. I have just received a separate box, way bigger than needed, which I am going to move the pi, the 7i90, and a large group of snubber diodes so that no input can go above about 4.75 volts, nor below ground more than the on bias of a 1n914, and bypassed to ground with a .005 ceramic capacitor. Each i/o line will be so protected. The way the spi cable leaves the pi and connects to the 7i90 is problem because just about the only way to run it that doesn't need a pin order swap, is to run it over the pi, or under it. Running the pi on 1" high standoff, it can run under the pi and be about 2" shorter than my present lashup, which has to improve the noise margin of the spi bus. That leaves room for the hdmi cable to clear the 7i90 sitting on much lower standoffs. And thats a ground loop right there because the monitor has its own power cord ground, so thats a good noise pickup src. > Fiber optic requires serialization, added a lot of new complexity and > latency, for no real benefit. Serialization? How so? Maybe with toslink. Here the led is on, or its off. Signal latencies are nanoseconds in single digit quantities. This is not, and never will be, an encoded serial bit stream anyplace but over the spi cable. Anything else is a logic signal of totally arbitrary duration. With enough noise on it to destroy a 7i90. BTDT, 3 too many times already. And I've just clicked on a bigger box to put the power electronics in, so I will be able to put the vfd inside it. And I'd really like to make ALL of those control interconnects fiber. Presently thats 4 to drive the steppers, 3 to drive the SpinX1, and two to drive a pair of SSR's switching all motor power with the LCNC enable button. 9 total. With the links I sent earlier, the only missing piece is the fiber interconnection, which is not a toslink style connector & therefore 1/4 the cost since there shouldn't be a toslink/firewire royalty to pay per socket. Apparently those royalties are still being collected despite Jack Tramiel's passing some years ago. > Danny Cheers, Gene Heskett -- "There are four boxes to be used in defense of liberty: soap, ballot, jury, and ammo. Please use in that order." -Ed Howdershelt (Author) Genes Web page <http://geneslinuxbox.net:6309/gene> ------------------------------------------------------------------------------ Check out the vibrant tech community on one of the world's most engaging tech sites, Slashdot.org! http://sdm.link/slashdot _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
