On Thu, 2010-12-09 at 20:06 -0800, Kirk Wallace wrote: > I blew out the only 74HC (74HC04 NAND) part in my junk box, so I cut my > charge pump circuit down to this: > > ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ > _ _ > Buffer Card Output _| |_| |_ Charge pump in servo thread = 1kHz 0-5V > ---------+ > | > === C1 .01uF > | O'Scope > +-|>--+--|>--+-----+----------- > | | | > | C2 === \ > | .01uF | / R1 15k > | | \ > V (gnd) V V > > ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ > > I played with different caps I had on hand and got the best results > with .01 uF for both C1 and C2 and 15k for R1. Even with R1 removed the > output would decay pretty rapidly, so I had to bump C1 up enough to > offset the leakage. Anything larger for C2 didn't seem to fully charge. > Then I sized R1 to get a sub 1 second drop, so would probably trip the > output at 200 to 300ms after losing the input signal. I suppose a CMOS > input and the scope should be a similar load, so the timing should not > change much if I add a Schmidt buffer to the output? > > I also wired this up: > > +--------- O'Scope > _ _ | > _| |_| | | C1 .01uF > -----------\/\/-----+---||--+ > R1 15k | > V (gnd) > > If T=RC, T=15000x.00001=.15 ? > On the scope, I got a shark fin like signal where most of the signal > change occurred by 200ms, so I guess this confirms the .15 for T above? > I didn't quite understand what I read on Wikipedia -- something like RC > is the value where the signal change is at around 63% of the signal > swing? I suppose I could use this circuit to measure caps with C=T/R > with T@63% of signal? I'll have to play with this some more.
Hi, (Hope is not to late...) Why don't you use one of Mariss Freimanis circuits ?!? http://www.artofcnc.ca/ChargePumpSafety.pdf or this from EDN "Hardware watchdog timer accepts range of frequencies" http://www.edn.com/file/25543-Hardware_watchdog_timer_accepts_range_of_frequencies_PDF.pdf Florin ------------------------------------------------------------------------------ Colocation vs. Managed Hosting A question and answer guide to determining the best fit for your organization - today and in the future. http://p.sf.net/sfu/internap-sfd2d _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
