thanks gene and andy looks like i have some more reading to do i will see whats available here and see what i can come up with
On 17-03-27 01:29 AM, Gene Heskett wrote: > On Monday 27 March 2017 01:38:13 linden wrote: > >> An other question for the Electronics experts on here; >> >> Is there a simple elegant way to drive the digital input 15 of the >> servo drive high to enable the servo using a digital output from the >> mesa 7i76e. I have attached a drawing using a relay and the examples >> from the dmm manual. Any ideas or suggestions would be greatly >> appreciated. I am afraid i know just enough to be dangerous and am a >> little leery of blowing out the io pins. >> >> thanks linden > The switched line fom the 7i76e will need a snubber diode, connected > between TB5-17 and the power supply rail, polarised to prevent the > inductance of the relay coil from putting a back emf spike more than the > on drop of the diode above the supply rail. Without that, the 7i76e will > have a good chance to be blown the first time the relay is turned off. > > The current flow thru the diode as the 7i76e turns off will prolong the > on-time of the relay, but thats not more than 10 milliseconds, and the > relay is probably slower than that. > > Current flow is always into the point of the symbolic arrow used on a > schematic, so the back of the point is the anode. Connect the anode to > TB5-17, and the cathode, marked by a ring mark on the end of the > package, should be connected to the + supply rail at the 7i76e. A > 1n914, which can be had in hundred packs for a couple dollars, is > probably sufficient for a small signaling relay. Big power type > rectifiers are also much slower than the 1n914, and may not be fast > enough to clamp off that turnoff spike. > > It may be that instead of the relay, an opto-isolator could pull the ena > line down, and that wuld not have the relay coils back emf spike at > turnoff. If it only takes 2 or 3 milliamps of current sink to do it, > I'd use the isolator & not muck with the relay. That will need a > current limit R, 200 ohms or thereabouts, in series with the input pin. > > Most logic circuits can sink more current than they can source, so the > mesa cards prefer that the on condition for the gear being controlled, > is a logic zero. Default power up is as an input, floating high. Thay > way you don't get surprise startups when turning stuff on it the > mornings. > > Oh, and wear one of those grounding wrist straps when working on this > stuff, a lesson I've recently learned. > > Cheers, Gene Heskett ------------------------------------------------------------------------------ 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 [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
