Re: How inaccurate is a 555 or 7555 REALLY?


mri_bob wrote:
i did not make up the .005% spec for the 555. It is on the first page of
National's data ***. the poster said he wanted .1% and i said the 555
would not be the controlling factor.

It isn't the whole story, like most manufacturer's specifications.

as for prototype/production issues, the guy said he wanted to make one, he
didn't say 1000. your experience in a production environment is
irrelevant.

If he isn't in a production environment, how many capacitors does he
have to buy to find one that drifts the right way to the right extent?
Bearing in mind that capacitors from a single batch are usualy a lot
more similar that parts from successive batches.

Selecting parts is a mugs games.

i said crystals were good enough. i don't know why you are arguing that
point? you seem to be misstating my position on that one just so you can
disagree with me.

10MHz crystals are a lot better than 32768Hz crystals. My Farnell
catalogue is back i Nijmegen, which made it difficult to be
quantitative.

i said .1% is a minute and a half a DAY and a $2 watch is better than
that,

Mainly because it is temperature controlled by your wrist.

then you rant about needing to go to a lot of trouble to get .5
seconds per day and say that is .01% Well, there are 86,400 seconds in a
day so .01% is 8.6 seconds. You are off by over an order of magnitude and
you are berating me saying i don't know what i'm talking about?

That was a typo - it should have been 0.001% or +/-5ppm. I used to
worry about that sort of error - now I just try and cross-check.
Everybody makes an error like that about once every 30 minutes when
sober ...

and you do not need automatic frequency control in a radio to keep it from
drifting 100 kHz.

Once it has warmed up

nor do you need a PLL. a cheap simple fm ham receiver


Which has an operator to provide AFC via a slow PLL

with no AFC will not drift that much by an order of magnitude.

Regular FM radios have a PLL to provide AFC, lacking an operator
prepared to act as a dumb servo ina slow loop.

To quote you: "Try to understand the technology you pontificate about before you
claim to be getting real"

I do, you don't. Pity about that.

--
Bill Sloman, Nijmegen (but in Sydney at the moment, and a glass or two
f red wine off sober)

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