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 -- "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
