Adding despiking capacitors

You can add these capacitors in the schematic like you would add any other part and connect them to the chip the way you would connect any other parts.  On the schematic, it doesn't matter where you place the capacitors physically, but they should be connected directly to the chip electrically.  When you make your board, then you can place the parts very close together.

The INVOKE command is used for the chips themselves and allows you to place part of the chip on your schematic.  For example, if you have a quad op amp, you can invoke any of the four op amp circuits.  If you don't use one or more of the op amps, you don't have to invoke them and they won't show on the schematic.

Dear Don Hersey,  mcb1 + Doug Wellington,

Wow!!!! Very fast and awesome response!! Thank you so much gentlemen. Yes, very correct, one just has to place them in the schematic and then later move them closer to the chips. I am now after I read the insight on, "over use" of these caps........thinking of.......instead of one cap per chip, perhaps will use......one cap per two chips. It is very easy to overdo this decoupling/despiking thing. The currents will start to breath instead of flow on the tracks.

I am designing my power tracks 3 times ticker then my signal tracks also, much better for the overall impedance.

Thx again gentlemen!

Cheers,

peter

Yes it is possible to "over decouple" your supply by having too many large capacitors  however it's generally better to have many small (say0.1uf) capacitors by every chip than having a larger one every so often. Each small capacitor supplies decoupling to each chip in turn which is what you are after!

Yes it is possible to "over decouple" your supply by having too many large capacitors  however it's generally better to have many small (say0.1uf) capacitors by every chip than having a larger one every so often. Each small capacitor supplies decoupling to each chip in turn which is what you are after!

Decoupling caps actually provide 2 services - most people think they help

keep the power clean to the logic chips.  That is true, HOWEVER, they also

are there to prevent the logic chips from putting their switching noise

back on the power line for the other chips.  Many people look at from the

standpoint of if the power is clean, then everything on the board will be

fine and forget that switching transients from different families of logic

can be pretty nasty.  TTL used to have a bunch of issues like that (but I

date myself ... )

mikey

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mikey

You are so correct.

I guess as old timers we remember our training and sort of jump to the end ..ie a clean power supply.

Knowing that to have a clean power supply you have removed the mains/switching ripple at the supply, then removed the switching transients caused by the logic (or other) again at the source.

We've also ignored that we know the appropriate type of capacitor to use for each instance.

Thanks for reminding me to not overlook the bits that became ingrained during our training.

Mark

Ah the old days of 100 mixed chips on a wirewrapped card.  We frantically

sprinkled 0.1ufd ceramic caps all over the place (remember the IC sockets

with the 0.1ufd caps in them?).  Without proper bypassing, you could spend

weeks trying to troubleshoot a board only to discover the issue was

switching transients causing all your problems.  Didn't have these issues

with vacuum tubes, but I do remember getting some nasty shocks poking

around in there

mikey

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Web access to CadSoft support forums at www.eaglecentral.ca.  Where the CadSoft EAGLE community meets.

100 mixed chips on a wirewrapped card

(remember the IC socketswith the 0.1ufd caps in them?

I remember them but luckily never had to work with them.

I do remember getting some nasty shocks poking around in there

I recall one of my fellow workers whom had grown used to 12v equipment, doing some leaping around as the high voltage got him ...

When you talk about valves now some of them think you're bonkers .... why would you have a thing that stops air coming out in your electronics ...

I said in another post ...

people don't understand magic smoke ....  even after you explain it doesn't work if you release it .... they still don't get it.

We should go back to valves so they can see where its held.

Mark

How about the predecessor to the Integrated Circuit from the vacuum tube

(valve) side - remember the old "compactrons" - they actually had several

devices inside one glass envelope.  They were around for a few years.  And,

if you had a bunch of tube equipment, you had no need for heat in your

building!  Yeah, 200-400 volts could get your attention if you got your

fingers on it while poking around.  Everybody laughed, you got back up off

the floor and went back to work

mikey

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remember the old "compactrons"

No sorry don't recall those, but I do recall the introduction of 'thick film technology'

An engineer came and spoke to us and told us they were far too complicated for us to understand.

(he was lucky the high voltage was away that day)

We used the valve transmitter for the taxi channel as a 'pie warmer' (before microwaves) at a station ... very handy.

Mark

An interesting read:  http://en.wikipedia.org/wiki/Compactron

I remember back in '68 or so Popular Electronics had an article on a guy

with some sort of surplus computer he purchased. All tubes.  Took up his

whole shop and required something like a 20 ton air conditioner to keep it

cool.

mikey

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And that was with no redundant cooling system.

Once we went to transistorized equipment, the rodent problem in winter seemed to also drop.

Mark