On Monday 04 May 2009, Erik Christiansen wrote: >On Sun, May 03, 2009 at 09:05:54PM -0400, Gene Heskett wrote: >> I used 2 pieces of brass tubing from the model hobby store that slip >> inside the next larger size. 1/4" & the next size smaller. I cut a pair >> of windows in the outside 1/4" tube such that a one piece opto interrupter >> (ir led on one side, ir photo-transistor looking at the led across the air >> gap) fit by friction across the slots. Then in the smaller tube I cut a >> longer pair of matching windows in, using diamond wheels in a dremel cuz >> that stuff bends easily, too easily to saw, filled the top with solder so >> a ball point pen spring could rest on it pushing it down, made a steel >> pointed plugin for the bottom of it, and slid a piece of a black cable tie >> inside it to act as the light valve. The outside tube is swaged in at the >> top just enough to trap the ball point pen spring. > >Gene, that's a super clear word picture. Good enough to build from. I >hadn't imagined a simple shutter (the piece of black cable tie), >transitting the light beam from one side (below), cutting off the light >beam in anything but a gradual manner. > >The little bagful of Sharp opto interrupters I bought last week have a >0.5 mm slit on the detector side of the slot. Ahh ... with a schmitt >trigger (or just a comparator with minimal hysteresis) on the detector >output, we can trigger on a (reasonably) fixed light level, and so a >fixed point in the 0.5 mm beam transit. > >Many thanks for the description. (I'll still be in the audience when the >pictures are published. :-) > They are now included at <http://gene.homelinux.net:85/gene/emc> as 'probe-*.jpg'
These opto's I used have about a .150" gap. It holds the thing together when assembled. I don't recall now if they have schmidt outputs or not. Now this is Off Topic: As for the accuracy, I have a home made version, build up from small pieces of cherry to hold the led and transistors, gapped wide enough to straddle the beam on my ancient Ohaus 505 powder scale and use it to control an H&R stepper driver kit, which in turn controls a large ecomony sized home made powder dribbler that can hold over half a pound of powder. I found the action as the beam moves very sudden, so I used 2 photo-transistors stacked vertically in parallel as the detectors in order to gradualize its response, along with a very dim led, but its still so sudden that I had to build a very weak spring in under the scale beam to hold it to about -.15 gr position when the pan is empty. Positioned carefully so that it doesn't touch the beam by about 20 thou when its in balance. The stepper slows down very very quickly in the last 2 grains dumped, and it stops the stepper when the beam is at about -.1gr and the beam actually coasts into balance when everything is right, including which side your chaw of kentucky twist is held. (yours maybe, not mine, I haven't used tobacco in 20 years) But I can get +- .02 grain accuracy out of it, 50 charges in a row, and that is what counts. I have to shade it from room lights with a hunk of scotch 88 over the top of it as the lights effect it about .1 grains. Obviously I do a little target shooting too. Enough that 3 boxes of factory shells, and a couple shoeboxes of old mill brass from Camp Perry in the mid 60's, have now about burned out the 2nd barrel (one of Ed Shilen's) on the 22-250, and 3 barrels on my Ackley-06 I use for my venison getter. :) It has had too much of the WV hunting season which corresponds to our fall monsoon here, aka rust pits near the muzzle. So now I carry a bag of balloons to pull over the muzzle & shoot through them when I'm out in the rain. But I suspect it will take a trip to Cross Lanes WV to get it fixed, another fresh Douglas Supreme before its again a one minute gun. Stainless I think this time. It won't last as long before the throat goes away, but won't rust either. At my age now, I don't expect to wear the next barrel out. One of my boys might though. :-) >Cheers, >Erik -- Cheers, Gene "There are four boxes to be used in defense of liberty: soap, ballot, jury, and ammo. Please use in that order." -Ed Howdershelt (Author) Adapt. Enjoy. Survive. ------------------------------------------------------------------------------ Register Now & Save for Velocity, the Web Performance & Operations Conference from O'Reilly Media. Velocity features a full day of expert-led, hands-on workshops and two days of sessions from industry leaders in dedicated Performance & Operations tracks. Use code vel09scf and Save an extra 15% before 5/3. http://p.sf.net/sfu/velocityconf _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
