On Sun, Dec 12, 2010 at 10:49:33AM -0800, Kirk Wallace wrote: > > > > I need to add a voltage regulator and filter caps, but there is no magic > > > there. I've noticed Matt's circuit is leaner because it doesn't need > > > one. My circuit might be improved with some I/O protection, but that > > > will make it more complex. > > > > For just one 74HC14, a resistor and 5.1v zener diode will do. > > I'm used to a Zener on a gate input to limit the input voltage, but the > circuit input is an opto-isolator which is not so delicate.
Sorry for confusing by placing the zener comment one sentence too late. It was intended to suggest using the zener in place of a voltage regulator IC. If there's little else requiring +5v, then a resistor and 400 mW zener will do to supply tens of milliamps at 5.1v. (Perhaps 5.2v when the load is low, and the zener has to shunt more.) > I noticed an "extra" diode on my Bandit drivers opto's. My guess is > that the opto diode has a lower reverse break-down voltage and the > additional diode shores it up? The reverse breakdown voltage of a LED is not high, so the normal input voltage applied across LED and series resistor can easily be enough to destroy the LED, if accidentally reversed. (I avoid putting even 5v reverse polarity on them) The series diode blocks that. (My habit is to connect any old diode backwards across the LED, to clamp reverse bias at 0.7 or so. Any reversed drive is then dropped across the series resistor.) > I'm concerned about the buffer output, which could have a > pull-up, pull-down, and or current limit resistor. I suppose a Zener on > the output could help with over-voltage or reverse voltage, but the > buffer is supposed to be driving an input not a source, but an inductive > load could be a source, but... I usually put off the output components > until I know what I'm going to hook it up to. Though, this doesn't help > in coming up with a more generic consumer grade product. That's tricky. You never know what people will do with an exposed output. Perhaps a small relay, with flywheel diode across the coil, even if a transistor is used to drive it, would both provide a robust output, and be easy to include in an Estop chain? Erik ------------------------------------------------------------------------------ Oracle to DB2 Conversion Guide: Learn learn about native support for PL/SQL, new data types, scalar functions, improved concurrency, built-in packages, OCI, SQL*Plus, data movement tools, best practices and more. http://p.sf.net/sfu/oracle-sfdev2dev _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
