On Mon, 2008-04-28 at 21:08 -0400, John Kasunich wrote: ... snip > After I wrote my reply I looked closer at the schematic and saw the how > big your caps are. I also noticed that you are using an LS14. I used > much smaller caps, probably 0.1uF for the filter and 0.01uF or smaller > for the pumps. I used proportionally higher resistors to get the time > constants I wanted, but the net result is less loading on the '14 > sections that are driving the pump.
I started with .1 uF pump caps but could not get enough voltage. When I put the 2.2 uF caps, I got what I wanted and went on to other issues. One of these days, it would be nice to learn spice and do a proper job of design. > In your case, the input current requirements of the LS14 make it > interesting. IIRC, LS inputs go high when open - you need to make sure > your load resistor R5 is low enough to ensure a logic zero when the pump > is off. If you've socketed the chip, I'd strongly consider replacing it > with CMOS one, like an HC or HCT. I checked for proper output (low) for steady high and steady low input signals. I used the LS because that is what I found in a pile of telecomm boards I use for my own little RadioShack. I have never paid much attention to the technology types, so I appreciate your advise and will take it into consideration when I put my Digikey order together. For the current circuit it might be helpful if I got the scope out and looked at the signals along the way. > Since the CMOS parts have very high DC input impedance, you could put > 10K to 50K between the top of R5 and the input to the chip. That would > greatly limit any current that might flow into internal protection > diodes, and make the clamp issue go away. And since the signal is DC at this point, switching speed is not an issue, so the resistor would not have any down side(?). > The tradeoff between HC and HCT is driven mostly by the input from the > PC (pin 5). HC is better for the output section, since I think the HC > thresholds are about mid-rail. HCT thresholds are lower, and are a good > choice if the parport might be driving only 3.3V. > > Regards, > > John Kasunich -- Kirk Wallace (California, USA http://www.wallacecompany.com/machine_shop/ Hardinge HNC/EMC CNC lathe, Bridgeport mill conversion, doing XY now, Zubal lathe conversion pending Craftsman AA 109 restoration Shizuoka ST-N/EMC CNC) ------------------------------------------------------------------------- This SF.net email is sponsored by the 2008 JavaOne(SM) Conference Don't miss this year's exciting event. There's still time to save $100. Use priority code J8TL2D2. http://ad.doubleclick.net/clk;198757673;13503038;p?http://java.sun.com/javaone _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
