Ping John Larkin: Question on MAX
in [Design]
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From: krw on 31 May 2010 23:18 On Mon, 31 May 2010 19:46:11 -0700, "Joel Koltner" <zapwireDASHgroups(a)yahoo.com> wrote: >"John Larkin" <jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote in message >news:atp806ddh0j8oqqql9n1ujvm3s1h21b2uc(a)4ax.com... >> "DESC" 0603 SURFACE MOUNT CAPACITOR >> >> Where HTI is our in-house MAX stock number. Pretty ugly, no? PITA to >> parse. > >Having the attribute names in quotes but the attribute values not in quotes >sure is a pain... > >> Parsing and comparing the values was a little tricky. 0.33uF was not >> exactly the same as 330nF in floating point > >I was wondering if you were going to deal with this... > >I've often felt a tool that goes around and "standardizes" all the decoupling >caps to 100nF or 0.1uF or whatever one prefers would be useful. Not because >I'm a nazi when it comes to suggesting that there should be hard rules for >when fractional values are OK or not (although some people around here >are...), but rather because I think there's value in having consistentcy in >your schematic: 100nF vs. 0.1uF vs. 0u1 (ouch!) tends to just say something >about how old you are (when you went to school) or if you're in the U.S. or >Europe, but different styles throughout the schematic makes you look >schizophrenic, which is rather more worrisome. We just skip nF completely. The only question is whether it's .001 (uF assumed), or 1000pF. I guess even that ends up dependent on where it's used. Decoupling it's .001 and in a filter it's 1000pF. Yes, a mess.
From: Joel Koltner on 31 May 2010 23:48 <krw(a)att.bizzzzzzzzzzzz> wrote in message news:0su806dlahcpgu29adn6d4i9c44j8tgid1(a)4ax.com... > We just skip nF completely. The only question is whether it's .001 (uF > assumed), or 1000pF. I guess even that ends up dependent on where it's > used. > Decoupling it's .001 and in a filter it's 1000pF. Yes, a mess. This is an area where I think those newly minted graduates do bring something of value to older engineers -- they don't shun nF. :-) We don't have any particularly hard and fast rules, but in general all capacitors and inductors get their full units spelled out (22nH, 100pF, etc.), whereas resistors don't have "ohms" added *unless they're 1-999 ohms* and hence would otherwise have no suffix at all. This is a sort of compromise between "ohms" spelled out looking a little dorky since ORCAD won't let you use a proper Omega symbol but still wanting at least something to suggest you didn't just forget a "k" or "M". I am guilty of doing dumb things like having just labeled a bunch of inductor in nH and then proceeding to label a bypass cap as 100nH rather than 100nF. Oops... When we first started implementing our new MRP system some years ago now I made the suggestion that, when searching for parts, It Would Be Nice to have the system be smart enough to understand the standard metric suffixes so that when someone creates a part that's 100nF it can still be found whether someone searches for 0.1uF, 100nF, 100000pF, 1e-9F, or any other silly combination you might think up. I'm not expecting anything that useful will actually end up being available (I'm not at all impressed with the flexibility of these big MRP systems -- seems like many of them aren't much better today that what existed 30 years ago), but I'm crossing my fingers that someday I'll be pleasantly surprised. ---Joel
From: krw on 1 Jun 2010 00:16 On Mon, 31 May 2010 20:48:14 -0700, "Joel Koltner" <zapwireDASHgroups(a)yahoo.com> wrote: ><krw(a)att.bizzzzzzzzzzzz> wrote in message >news:0su806dlahcpgu29adn6d4i9c44j8tgid1(a)4ax.com... >> We just skip nF completely. The only question is whether it's .001 (uF >> assumed), or 1000pF. I guess even that ends up dependent on where it's >> used. >> Decoupling it's .001 and in a filter it's 1000pF. Yes, a mess. > >This is an area where I think those newly minted graduates do bring something >of value to older engineers -- they don't shun nF. :-) I didn't either. In fact the hybrid I first worked on was all in nF because all the caps were in that range. They don't so I stopped. I don't really care, nF is easily enough covered by uF and pF. >We don't have any particularly hard and fast rules, but in general all >capacitors and inductors get their full units spelled out (22nH, 100pF, etc.), >whereas resistors don't have "ohms" added *unless they're 1-999 ohms* and >hence would otherwise have no suffix at all. This is a sort of compromise >between "ohms" spelled out looking a little dorky since ORCAD won't let you >use a proper Omega symbol but still wanting at least something to suggest you >didn't just forget a "k" or "M". We could, but there are more significant digits in resistor values and the vast majority of resistors are in the 1K to 1M range. I significant percentage are 10K. ;-) I could argue that you should be using mF, too, to be consistent. ;-) >I am guilty of doing dumb things like having just labeled a bunch of inductor >in nH and then proceeding to label a bypass cap as 100nH rather than 100nF. >Oops... See, you wouldn't make that mistake if you labeled them ".1". ;-) >When we first started implementing our new MRP system some years ago now I >made the suggestion that, when searching for parts, It Would Be Nice to have >the system be smart enough to understand the standard metric suffixes so that >when someone creates a part that's 100nF it can still be found whether someone >searches for 0.1uF, 100nF, 100000pF, 1e-9F, or any other silly combination you >might think up. Amen! As it is, I do this in a Excel spreadsheet but it's a PITA. The parts system should take care of that administrivia. That's what computers (are supposed to) do. As I'm told, our system was quite expensive, yet one couldn't design a much worse UI on purpose. >I'm not expecting anything that useful will actually end up being available >(I'm not at all impressed with the flexibility of these big MRP systems -- >seems like many of them aren't much better today that what existed 30 years >ago), but I'm crossing my fingers that someday I'll be pleasantly surprised. Why would you even hope for sanity? It's just something to live with.
From: John Larkin on 1 Jun 2010 00:28 On Mon, 31 May 2010 20:48:14 -0700, "Joel Koltner" <zapwireDASHgroups(a)yahoo.com> wrote: ><krw(a)att.bizzzzzzzzzzzz> wrote in message >news:0su806dlahcpgu29adn6d4i9c44j8tgid1(a)4ax.com... >> We just skip nF completely. The only question is whether it's .001 (uF >> assumed), or 1000pF. I guess even that ends up dependent on where it's >> used. >> Decoupling it's .001 and in a filter it's 1000pF. Yes, a mess. > >This is an area where I think those newly minted graduates do bring something >of value to older engineers -- they don't shun nF. :-) > >We don't have any particularly hard and fast rules, but in general all >capacitors and inductors get their full units spelled out (22nH, 100pF, etc.), >whereas resistors don't have "ohms" added *unless they're 1-999 ohms* and >hence would otherwise have no suffix at all. This is a sort of compromise >between "ohms" spelled out looking a little dorky since ORCAD won't let you >use a proper Omega symbol but still wanting at least something to suggest you >didn't just forget a "k" or "M". We have standardized on pF, nF, uF, and, sadly, mF. Numbers are never below 1, except 0.5 pF maybe, and never start with a decimal point. Resistors are 12R, 3.01K, 22M, 3G, 1T. I suppose I'd parse 14mR or just 14m as 14 milliohms. "12" will parse as 12 ohms. We will NEVER use the juvenile 4k7 thing. I'll enforce that in my will. Hmmm, maybe I should parse 2.2F properly, in case we buy some supercaps some day; I'm not doing that now. One more line of code. > >I am guilty of doing dumb things like having just labeled a bunch of inductor >in nH and then proceeding to label a bypass cap as 100nH rather than 100nF. >Oops... We are all shocked, shocked. It is fun when you ECO replace a resistor, like R99, on a board with a capacitor, which has to still be R99. I wonder what my crosschecker would do in that case. > >When we first started implementing our new MRP system some years ago now I >made the suggestion that, when searching for parts, It Would Be Nice to have >the system be smart enough to understand the standard metric suffixes so that >when someone creates a part that's 100nF it can still be found whether someone >searches for 0.1uF, 100nF, 100000pF, 1e-9F, or any other silly combination you >might think up. All our resistors and caps are... believe it or not... IN ORDER BY VALUE. That makes shopping for parts really nice. I also have a program that finds resistors in stock that approximate desired ratios. John
From: Nial Stewart on 1 Jun 2010 05:52
> being tied to the database has the advantage that you can choose > components you already have ....and have double sourced and have confirmed footprints! Nial. |