On Friday 14 October 2016 19:41:23 MC Cason wrote:
> On 10/14/2016 02:01 PM, Gene Heskett wrote:
> > On Friday 14 October 2016 14:45:31 Chris Albertson wrote:
> >> Typically 0.1 bypass caps REALLY to have to be physically close to
> >> the load they are bypassing. Within a few millimeters. Cut the
> >> leads short and bridge the power pins with the cap.
> >> Placing a larger cap farther away can't cause any harm but it is
> >> not going to do the same job.
> >> Reason: The real world is not the same as theory. All caps have
> >> an internal series resistance (ESR). Think of them as a cap and
> >> resister in series and model them that way too when you design the
> >> circuit. The ESR of a .1uF ceramic cap is nearly zero, but for the
> >> tantalum, you need to look it up in the data sheet.
> >> Why physically close to the load. Wire has non-zero impedance.
> >> Mainly in this case it is inductive. You need to minimize the
> >> value of the inductor between the 0.1 cap and the device.
> >> Apparently the manufacturer wants a low impedance power supply.
> >> Draw the circuit schematic with a the lead wire inductance and
> >> cap's ESR shown then you can see that needs to be minimized. Don't
> >> worry about space you candy 0.1 caps that are the size of a large
> >> grain of sand
> > Anyplace of note to source them?
> Here is one in a 01005 package (Metric 0402) 0.016"L x 0.008"W -
> (0.40mm x 0.20mm) :
> They are cheaper than the through hole caps that I normally buy.
> Hand soldering them will be a royal PIMA!
At .2mm x.4mm, you have that right, the pain will be in My Ass. My hands
are just starting to get nervous, which won't help a bit. And to see
them well, I might have to get some cataracts removed. That is about
the size of a comma in the newspaper! My hot air wand could blow it
away, never to be found again by anything but the vacuum cleaner. That
would fit across the gap between 2 traces, cut about as narrow as my
mill could make them. This is going to be fun, for some definition of
fun. I may even see if a bigger one, say about 1/8" long might be had.
Those I have played with a wee bit.
Thanks MC Cason.
> >> The usual way to mount these is to make a tiny PCB that has the
> >> device on to and a mounting hole and the passive parts like the
> >> capacitor(s) and a connector for the cable.
I considered that, but the magnets in the 667's are strong enough to
wiggle and crack the joints, so the 667s are super-glued to the bottom
of their protective trench's.
I'll have to reach a much bigger board a couple inches away with wire
wrapping wire before it graduates to a 5 conductor cable to snake its
way out of the back rear of the spindle housing. Stress relief & all
that twaddle. :-)
> >> All that said, it will likely work OK if you can get that small ca
> >> reasonably close. Better to get the 0.1 closer then a larger one
> >> farther way as the goal is to minimize the amount of wire
> >> And using a larger cap is no substitute for the .01 either because
> >> I bet the .1 was spec'd mainly for its low ESR, not because it
> >> needed to be exactly 0.1uF
> > As a CET, I am well aware of all that, including the inductance of
> > 2" of wire.
> > As for the ESR, tantalums are generally sub ohmic too. For half a
> > century or more. Its reverse bias that nails them to the fence, even
> > a few millivolts will do it eventually.
> > Any caps on the leads will have to be not longer than the 667 is
> > wide, and not more than half its thickness.
> > Thanks Chris.
> >> On Fri, Oct 14, 2016 at 9:51 AM, Gene Heskett
> >> <ghesk...@shentel.net>
> > wrote:
> >>> Greetings everybody;
> >>> A bit too cold this morning to go out to the shop and saw out the
> >>> thicker spacers I am going to need to permanently mount the Z
> >>> motor and screw anchor.
> >>> So, not wanting to waste the day waiting for it to warm, I went
> >>> back to work on the encoder thing this morning.
> >>> I now have an additional tab of alu extending to the left to hold
> >>> one of these ATS667's as an index pulse generator, and have that
> >>> one s-glued in a bit beyond where the center of the glued on screw
> >>> passes by, hoping it won't trigger on a regular tooth.
> >>> But, I've never used any of these before. No clue as to their bad
> >>> habits.
> >>> The spec sheet I have shows a "required" .1 bypass to ground on
> >>> the VCC lead, but has anyone had any problems using just one for
> >>> all 3 devices? This thing is cramped for space for a bulky mylar
> >>> .1.
> >>> So I intend to put an even larger tantalum on the pcb, which will
> >>> be on the left face of this added tab as I can let it project
> >>> inward nearly 20 mm's in that space, lots of space before
> >>> encountering anything that moves there. That means I'll have to
> >>> paste some wrapping wire to extend the leads about 1" to get to
> >>> the pcb. So this bypass cap may be as much as 2" of wire away
> >>> from the device body.
> >>> Can anyone testify that the extra lead length is a problem?
> >>> Thanks all.
> >>> 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
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> > Cheers, Gene Heskett
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
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