How inaccurate is a 555 or 7555 REALLY?

And once you choose an R-C, what does those irregularities have to do with stability?

Most of the temperature variation in a 555 timer would come from the delay time through the comparators to the output.

Probably not.

Agreed.

...Jim Thompson

before you claim to be getting real" I do, you don't. Pity about that.

i guess i will have to turn in my engineering diploma then. i have run into clowns on newsgroups before who attacked other peoples ideas just so they could tell their own stories about how much they know, it's nothing new.

i was attempting to help a novice learn why it would be difficult but maybe not impossible to do it with a 555 if temperature was tightly controlled but that a microcomputer circuit would be better. bill has his own agenda which is different from mine. i'm finished with this topic. people who need to end their posts with insults have nothing to offer to me.

-bob

Thanks for all the great and useful data and information everyone, I really started a firestorm of argument on this topic. I'm happy to switch to the dividing circuits, but i'm stuck with using AA's... is there any packages that anyone can think of which will divide at that low of voltage that doesn't have minimum frequency limitations yet still pretty small?

Programmable solutions are acceptable, however I've gone crosseyed looking at datasheets that all show minium 3v with min Fout of xxxkHz instead of low hz ratings.

~Brendan

PS to Phil - not every> WildIrish wrote:

But making an oven to keep temperature within 3C is not difficult, so that part is not "totally impractical in the real world".

you

? "Nijmegen" ? *What* is that?

That ratio is temperature sensitive...

What "ratio" is that?

...Jim Thompson

in passing, i would like to address bill's ridiculous claim that a digital watch was only accurate to better than a minute or two a day because it was temperature regulated by the wearer's wrist. ridiculous nonsense that shows an ignorance of thermodynamics and of the stability of digital timepieces in general. How do you suppose the hundreds of millions of cheap digital wall clocks are thermally regulated?

-bob

Are you actually trying to generate a sine wave output?

Best regards, Spehro Pefhany

A town in the Netherlands, whose roots lie in the Novio Magnus military camp by the ancient Romans. Also the home of the Katholieke Universiteit where my wife went to the medical school.

Regards, Mikko

I wouldn't bother making the effort. Diploma's don't count for much. The IEEE admitted me as member 26 years ago without any evidence of any academic training in engineering (I do have a Ph.D. in Physical Chemistry) on the basis of a declaration from one of the IEEE members at EMI Central Research that I knew what I was talking about. I'd gotten two patents i the three years I'd worked there, so they may have had an exaggerated idea of my competence.

just so

And it does tend to stop people sounding off about stuff they don't know enough about.

Based on a fairly wearing month or so back in 1974 trying to do the same job for an over-optimistic boss. We ended up getting fairly close with an emitter-coupled multi-vibrator, but the temperature dependence of the Early effect was bad enough that even that circuit didn't make it.

Then you are condemned out of your own mouth.

Your second message in the thread - message 6 in the lst ends " let's get real, huh? " which is the kind of discourtesy I repay in kind. My own idea of my attitude on this news group is "polite until provoked" but John Larkin does keep on finding insults in my posts that I could have sworn weren't there when I composed them (and don't look much like insults to me when I reread them). Phil Allison would blame this on autism, but he blames a lot of stuff on autism. He's not an expert psychologist, unlike my wife's academic colleagues (who won't use me as a test subject any more, because I know too much).

The ratio of the ersistor calues in the (comparitor) divider.

just so

What makes you think resistor ratios have a TC?

Solid ratios is the only reason we can build analog IC's at all.

...Jim Thompson

- was I supposed to think otherwise ?

Your posts show a total lack of practical electronics knowledge.

Your alleged "engineering degree " is a worthless scrap of paper.

I absolutely stand by my comment:

" The size and performance criteria you have come up with make it a job for an expert. "

You still have a lot of growing to do - pal.

....... Phil

"mri_bob"

Must be a close relative of " Joe Blow"

Obviously, a worn watch undergoes a much smaller range of temperature variation than one that it not - hence the stability of its crystal based time keeping is much enhanced.

Battery operated clocks rely on the INDOOR room temp having a *long term * average that is not too far from 25C - their makers claim an accuracy of about 30 seconds a month, which is nothing wonderful.

Bob - do you have a diploma in utter stupidity or what ?

...... Phil

Hi Brendan Standard 74HC logic can work down to 2V, and you can get low voltage crystal oscillator modules. Some micros like the PIC and Atmel AVR series can work down to 2V too. That's enough headroom for a 2xAA battery supply.

You can also make your life a bit easier if needed by using a DC-DC converter to give you 5V from however many batteries you have.

Dave :) P.S. Ignore Phil, that's just the way he is unfortunately.

Thanks for your help. I can potentially bump up to 3v. Is there any 74HC or similar products that can perform divisions high enough to divide down a 10mhz oscillator in only ONE package? Someone early on suggested using a pair or 74HC's to do the job, is there any off the shelf dividers in on package capable of this assuming I switch to a 3V supply?

What dividers are used by wristwatches? they must take a 32768hz oscillator and divide it WAY down until it gets one second bursts to advance the stepper motors? What dividers do they use, they run at 1.5v right?

Thanks. That's unfortunate, he seems to know his stuff but exibits social issues.... i'd be afraid to work with a guy like him. Phil if you read this, don't waste your time on this thread anymore, we are all tired of you it appears, and I don't need or want your help. HOWEVER, I appreciate everyone else's time and energy in helping me to bridge gaps in my knowledge.

~Brendan

"WildIrish Narcissistic Asshole "

Take a look inside one some day.

You will first need to pull you head out of you arse in order to see anything.

Then grow up a lot more.

........ Phil