How do you design these days?
in [Design]
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From: krw on 4 Jan 2010 19:55 On Mon, 04 Jan 2010 16:52:09 +0000, Baron <baron.nospam(a)linuxmaniac.nospam.net> wrote: >Spehro Pefhany Inscribed thus: >> >> With the spindle Morse taper Loctited in so that the side forces don't >> loosen it up! >> >> Best regards, >> Spehro Pefhany > >I've never had a Morse taper fitting loosen due to side forces or had to >use Locktite on one. You haven't put any side pressure on one, then. This is a very common occurrence for woodworkers using their drill press as a drum sander; not a good thing to do.
From: krw on 4 Jan 2010 19:59 On Sun, 03 Jan 2010 22:33:34 -0800, John Larkin <jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote: >On Sun, 03 Jan 2010 19:43:46 -0600, krw <krw(a)att.bizzzzzzzzzzz> wrote: > >>On Sun, 03 Jan 2010 16:49:45 -0800, John Larkin >><jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote: >> >>>On Sun, 03 Jan 2010 14:15:52 -0600, krw <krw(a)att.bizzzzzzzzzzz> wrote: >>> >>>>On Sun, 03 Jan 2010 10:08:15 -0800, John Larkin >>>><jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote: >>>> >>>>>On Fri, 01 Jan 2010 19:19:42 -0600, krw <krw(a)att.bizzzzzzzzzzz> wrote: >>>>> >>>>>>On Fri, 01 Jan 2010 17:40:54 -0500, ehsjr <ehsjr(a)nospamverizon.net> >>>>>>wrote: >>>>>> >>>> >>>><snip> >>>> >>>>>>>You've got a steadier hand than I'll ever have. >>>>>>>I have to do it with a Dremel mounted in a drill press >>>>>>>adapter, and slide the board against guides clamped to >>>>>>>the bed. Even then ... :-( >>>>>> >>>>>>Sounds like you need a small milling machine. >>>>> >>>>>We had one of those PCB mills, on indefinite loan from a customer who >>>>>wasn't using it. It was such a hassle that we wound up not using it >>>>>too. >>>> >>>>Gotta be better than fence clamped to a drill press. >>>> >>>>>I can do the modest stuff with a knife and some kapton tape. After >>>>>that, it's easiest to just lay out a board and have a pcb house make a >>>>>few. >>>> >>>>You mean copper-clad kapton tape? >>> >>>No, just bits stuck to the copperclad and cut into patterns, as local >>>insulators. >> >>What good does that do? I guess I don't see the purpose of the >>insulator without a pad to solder to. Got a picture? > >Under the SO8... > >ftp://jjlarkin.lmi.net/BB_fast.JPG Neat. I would have thought you would have just hogged out the foil underneath. BTW, John, I've had some time to play with the fake caps and fake resistors. I looked up the pointer to your circuit in the archives but the pointee is gone. Any chance you could put it up again? Any other pointers would be very handy, too. I need something that's good for four quadrants (or at least bipolar currents). Thanks.
From: krw on 4 Jan 2010 20:04 On Mon, 4 Jan 2010 10:53:31 -0800, "Joel Koltner" <zapwireDASHgroups(a)yahoo.com> wrote: >"krw" <krw(a)att.bizzzzzzzzzzz> wrote in message >news:ngu1k5lciqj2c6h9svs4m69eu4nu9ih7ut(a)4ax.com... >> Maybe I'll try it, but I don't do much prototyping. We have a >> prototyping machine but bringing it up has always been on the "to do" >> list. > >My experience is that it's almost always is cheaper to have boards made out of >house (particularly as soon as you have enough vias that you're better off >with plated-through holes rather than just soldering in jumper wires) than on >a milling machine *so long as you can wait for a week-long turn*. If I can get a two sided board in a day, I'll take it. We haven't been in the prototype circuit mode, so it's something new. New is bad. >E.g., I can get, say, a 6"x8" boards with solder mask, silkscreen, >plated-through holes/vias, and 6/6 traces and spaces for something like $100 >if I'm willing to wait a week, whereas having our guys make a board like that >with the LPKF machine we have is probably more like $500 and they start to >look worried with designs rules tighter than about 8/8. I'll certainly think about prototype houses. I don't have anything planned for the immediate future, though. We're kinda slow in the hardware department, at least until the firmware guys catch up. :-( >But it is nice to have around if you just need a single side+ground plane >board (which often works fine for the RF test boards I do) and can live >without a silkscreen or soldermask and would like the board *today*. Yeah, it doesn't have to look pretty. There are a lot of "tools" I'd like to have, too. Proto circuits would work fine. Wire on perf board works too, but it's such a PITA and mechanically unreliable.
From: krw on 4 Jan 2010 20:11 On Mon, 4 Jan 2010 11:04:43 -0800, "Joel Koltner" <zapwireDASHgroups(a)yahoo.com> wrote: >> On Sun, 03 Jan 2010 10:19:37 -0800, John Larkin >>>One mistake we used to make too often was swapping V+ and V- on >>>opamps. Engineers tend to flip an opamp to make the feedback path look >>>nice (different for inverting/noninverting) and that moves the power >>>pins too. We check that really hard now. > >We've been bitten by that. Originally some of the op-amps didn't even have >their power pins labeled -- the idea was "Vcc is on the top, Vee is on the >bottom" -- which of course is almost guaranteed to create an error if someone >flips a symbols. So now we require that all pins are labeled... > >I like Keith's idea of adding an alternative view so that power pins can >always end up with Vcc on top and Vee on the bottom. It's always been a >battle with the techs to get them to add more than one view of a part -- they >were really annoyed when I asked for about a half-dozen views for the >"universal" logic gate ICs (NC7SZ57 and NC7SZ58). "They" can get annoyed. The boss wants better schematics (they are a mess). He's not going to get entirely what he wants as long as they insist on WhoreCad, but that discussion was a few months ago. >Some tools make this sort of thing easier than others... ORCAD, for instance, >has the notion that a "part" can have only two views (they were thinking >"normal" and DeMorgan) and exactly one footprint. We use OrCrap, too. If you think about it, swapping the input pins of an opamp is sorta a DeMorgan thing. ;-) That's exactly what I have the layout guy/librarian do. With unit logic I have him do the DeMorgan thing - inverters, too. >Pulsonix is far more >powerful in that if keeps symbols, footprints, and parts all in separate >libraries and you can have a part consist of as many different symbols and >footprints as you feel like. I seem to recall that PADS is somewhere >inbetween those two extremes... (Obviously with any tools you can just create >multiple parts to work around such restrictions, but then if you discover an >error in one you have to make sure you correct all of the "equivalent" parts.) I don't like that, at all. As you point out, it's virtually impossible to make sure corrections are made everywhere. Errors are quite embarrassing the second time around.
From: krw on 4 Jan 2010 20:19
On Mon, 4 Jan 2010 15:02:59 -0800, "Joel Koltner" <zapwireDASHgroups(a)yahoo.com> wrote: >Hi Mark, > >"markp" <map.nospam(a)f2s.com> wrote in message >news:7qf5u7Fk7nU1(a)mid.individual.net... >> I have used Orcad Capture quite extensively, it actually has the concept of >> multi-part schematic symbols. There are two options, heterogenous or >> homogenous parts (i.e. different part symbols, or the same part symbol for >> all parts). If you define a 4 gate opamp as heterogenous with 5 parts you >> can create the 4 opamp gates with their repective pin numbers for each, and >> a fifth part with just the power supply pins only. That way you can flip or >> rotate the individual gates without affecting the power supply part. > >Agreed, that is useful, and I do the same thing for, e.g., quad or hex logic >gates (...also prompting whining from some people who haven't seen this done >previously). For dual op-amps, I think to date I usually just add the power >pins to both of them (and the DRC function tells me if I didn't connect them >both the same way), but even there I can understand someone splitting off a >separate power block, and it makes lots of sense for a quad op-amp. That's the argument I get from the layout guy. I'd rather just have two heterogeneous parts, one "gate" and one power. That way I can define the part usage later. Power can be placed with decoupling. With power pins on both parts of a dual op-amp, showing decoupling gets difficult. >The nice thing about CAD packages that let you have as many symbols as you >want for a given part is that you don't have to debate these things with your >fellow engineers or techs -- I want a quad op-amp symbol that shows all four >op-amps together and 2 power pins, I can have it. You want 4 separate symbols >plus a little power block, you can have it. Yet we're both still linked to >the same footprint, the same manufacturer's part no., etc. (A more concrete >example of this that I use is bussed resistor packages -- sometimes I'd like >all 4 or 8 or however many of them displayed as one symbol right next to each >other, other times I'd like all discrete symbols.) As you pointed out earlier, though, this can lead to corrections not being propagated to all symbols. >> A minor bug-bear I have though is that if you forget to put the power supply >> part on the schematic it won't flag it up as having unconnected power pins >> in the DRC (at least in the older versions of Capture). > >I make the power block the first "gate," so it shows up immediately when you >go to place the part. Hence it requires additional effort to forget about it. >:-) I make it the last, to get it out of the way. I generally create the "gates" from the front of the schematic to the back and the power page(s) at the rear of the schematic. |