On Tuesday 13 November 2012 19:17:17 Viesturs Lācis did opine: > 2012/11/14 Gene Heskett <ghesk...@wdtv.com>: > > That is a good start. In view of the noise, I think I would add a quad > > of 1n914 type diodes, such that the noise can't rise too far above > > the 5volt line, or go too far below ground. Two with the cathode > > bands toward 5v, the anodes to A & B, and two more from a & B with > > their anodes connected to ground. It might save you a mysteriously > > blown chip at some point in the future. > > Thanks!
In fact, I think I would put those diodes about a 100 ohm resistor away from the chip pins, it will add to the protection they give. The chip itself, since both the diodes and the chip are si tech, they'll have about the same fwd voltage clamping action. By adding the 100 ohm resistors in series with the AB's on the chip, more of a noise overvoltage spike will be absorbed by the diodes. Someone else whose msg I didn't reply to seems to think that the A & B here, is the A and B from the encoder, but this is a differential receiver circuit so the A & B here, are actually connected to the encoder A and -A outputs, and an identical circuit then has as its A & B inputs, the B and - B outputs from the encoder. Similarly the I(Z?) and -I(Z?) (index pulse) outputs from the encoder are connected to a 3rd identical circuits A & B inputs, so there are in fact, 6 wires and the shielding from those 3 circuits to the encoder, plus of course the shielding which should be grounded close to the gnd point of all 3 of these circuits, covering as much of the wires to the encoder as it can, but NOT actually connected to a ground at the encoder end of the connecting cable. The dis-continuous grounding furnishes shielding but prevents ground loops, where stray magnetic fields can create circulating currents that flow all the way around the loop, effectively becoming unwanted signals on their own. We call this the star topology because there is only one ground point, a bolt perhaps, and ALL other grounds connect to this single bolt, including the buildings static ground. Not its neutral since unbalanced loads phase to phase can and will create a lot of neutral current, complete with its associated I*R losses noise. Here in the U.S.A. at least, the ONLY place where these two circuits can legally meet, is in the service box immediately downstream of the service meter, and where by N.E.C. regs we must have pair of heavy gage wires from that buss, out to a pair of at least 6 foot ground rods, driven at least 6 feet apart. It must work fairly well, I haven't had any lightning damage here since I installed a new meter/breaker box in 2006, doing it according to code, since the original install from the '70's was done long before the code had any teeth. That OEM box is now a 60 amp subcircuit off the new 200 amp one. 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) My web page: <http://coyoteden.dyndns-free.com:85/gene> is up! Genuine happiness is when a wife sees a double chin on her husband's old girl friend. ------------------------------------------------------------------------------ Monitor your physical, virtual and cloud infrastructure from a single web console. Get in-depth insight into apps, servers, databases, vmware, SAP, cloud infrastructure, etc. Download 30-day Free Trial. Pricing starts from $795 for 25 servers or applications! http://p.sf.net/sfu/zoho_dev2dev_nov _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
