How inaccurate is a 555 or 7555 REALLY?

[Phil Allison]

"WildIrish Narcissistic Asshole "

What dividers are used by wristwatches?

** Custom chips are used, mounted direct on a PCB with no package.

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

 

[David L. Jones]

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?

You are in luck. A 10.752MHz crystal available from Farnell will give
you precisely 420Hz when divided by 25600.
But you are out of luck in that the ever-so-handy 74HC4060 divider IC
can not go that high (by one lousy bit would be believe it), otherwise
it would have been a single chip solution. The 74HC4060 has an internal
crystal oscillator too. So you'll need the 74HC4060 + an extra divider
chip.

http://www.fairchildsemi.com/ds/MM/MM74HC4060.pdf

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?

They use custom ASIC chips, not something you can get off the shelf.
Yes, it's effectively just a normal 32768 divider inside (plus a lot of
extra stuff of course)

Yep, either 1.5V (silver oxide battery) or 3V (lithium button cell)
operation.

Dave

 

[Robert Baer]

On Sun, 03 Dec 2006 19:19:05 GMT, Robert Baer



Jim Thompson wrote:



On Sun, 03 Dec 2006 06:44:33 GMT, Robert Baer

[snip]



Ignoring the insufficent supply voltage, the basic inaccuracy of the
555 design rests on the offset voltage of the comparitors combined with
the mismatch of the internal resistor divider ratios.


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.




Crudely speaking, 0.1% cannot be achieved with one 555.


Probably not.




If you want a relatively accurate frequency, look to crystal or
tuning fork oscillators using discrete SMT parts.


Agreed.

...Jim Thompson

That ratio is temperature sensitive...


What "ratio" is that?

...Jim Thompson

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

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

I suggest that you do some measuring...

 

[David L. Jones]

You are in luck. A 10.752MHz crystal available from Farnell will give
you precisely 420Hz when divided by 25600.
But you are out of luck in that the ever-so-handy 74HC4060 divider IC
can not go that high (by one lousy bit would be believe it), otherwise
it would have been a single chip solution. The 74HC4060 has an internal
crystal oscillator too. So you'll need the 74HC4060 + an extra divider
chip.

http://www.fairchildsemi.com/ds/MM/MM74HC4060.pdf

Oops, I forgot the extra divider gates needed. Perhaps the 74HCT40104
as someone else mentioned might be better...
Either way you need a 10.752MHz oscillator and some form of 15 stage
divider.

Space-wise I still think a small 8pin microcontroller is a better
solution. Do you need 50-50 duty cycle?, if so you'll need an extra D
flip-flop on on the output.

Dave

 

[[email protected]]

** And *nobody* thought of using cascode?

Didn't help. There wasn't all that much headroom t play with, and a
smaller collector-base bias meant that the Early effect was more
signiificant to start with - anything we won on the swings we lost on
the roundabouts.

My boss might have been over-optimistic, but he'd been trained at the
Royal Radar Establishment, working for Peter Baxandall, and his
electronics was very good indeed - I learned a great deal from him.

 

[Jim Thompson]

Jim Thompson wrote:

On Sun, 03 Dec 2006 19:19:05 GMT, Robert Baer
[snip]

That ratio is temperature sensitive...


What "ratio" is that?

...Jim Thompson

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

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

I suggest that you do some measuring...

I suggest you get you head out of your ass. I've been designing IC's
since the beginning of time... ratiometric is what it's all about.

...Jim Thompson

 

[John Fields]

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?

If you switch to 3V you can use common 74HC or 4000 family logic
and use whatever package size you need to fit into your box.

I've attached an LTSPICE circuit list using what amounts to a 4024
7-stage ripple counter, a 4013 dual D type flip-flop, and a decoder
made from 3 diodes and a resistor to realize a divide-by-78 circuit
which will output 420.103Hz from a 32768Hz input.

That's an error of about 0.025%

I would've used a 4060 counter, which includes the oscillator but,
unfortunately, this type of counter must be reset to zero once the
proper number of counts has been reached and, In a 4060, the
oscillator is stopped when the chip is reset.

32768Hz tuning fork crystals are cheap, available everywhere, and
application notes are available telling how to go about building a
clock oscillator using them, so I just showed the oscillator as a
32768Hz pulse generator.

The output of the circuit will be a 50% duty cycle 420.103Hz square
wave.


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[John Fields]

metal film


polyphenylidene sulphide


Fat chance. You'd have to stqabilise the voltage as well as the
temperature - the divider inside the 555 is a series of three
voltage-sensitive diffused silicon resistors.

I spent a month or so back in 1974 on exactly this problem, and
discarded the 555 very early on.


For a individiual capacitor - the temperature coefficient of wound
capacitors depends on the mechanical tesion in the dielectric, and the
tolerance on te temperature coefficient is all over the place.

Polyphenylidene sulphide sufrace mount capacitors are not wound (as far
as I know) and do better, but they still don't hack it at the 0.1%
level.


10MHz crystals are sold with a +/-0.1% absolute tolerance.

 

[Phil Allison]

"John Fields"

Instead of trying to remember your Farnell catalog, you ought to
visit crystal manufacturers' websites to fined out what's current.

20ppm at 25C for tuning fork crystals is easily achievable nowadays.

** Watch crystals with that accuracy have been available since the mid
1970s.

This site has some of the history of the tuning fork watch crystal.

http://www.ledwatches.net/articles/Statek Corporation - Watch Crystals.htm



........ Phil

 

[John Fields]

My own idea of my
attitude on this news group is "polite until provoked"

---
Which generally manifests itself as provocation = disagreement.
---

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).

---
Which is about the double standard you exact. If, in fact, your
posts are made without rancor, which is ridiculous on its face, you
insist that what must then be "carelessness" on your part be not
interpreted as insult, but that infinite care be taken with
correspondence directed to you in order that you not interpret it as
insult.
---

 

[John Fields]

"John Fields"




** Watch crystals with that accuracy have been available since the mid
1970s.

This site has some of the history of the tuning fork watch crystal.

http://www.ledwatches.net/articles/Statek Corporation - Watch Crystals.htm



....... Phil

---
Nice, thanks.

I still have a few of their early crystals, sealed in glass and, for
that time, pretty far out, being surface mount.

Speaking of early surface mount stuff, have you ever heard of a
device called a "Gifft Recorder"?

It was a SONAR transmitter/receiver invented by a man named Tom
Gifft which output about 1200 watts into a UQN transducer (if I
remember correctly) and used surface mount TI chips on all of its
PCBs.

Back when I was a young lad and worked for an outfit named "Marine
Acoustical Services" in Miami, Florida, I regularly went to sea as
the ship's radio officer and did double duty running the Gifft
Recorder.

One of its claims to fame was a stainless steel belt that had three
tabs welded to it, 120 degrees apart, which traversed a wet paper
belt which would change color when an echo was detected.

Also on the belt was a series of punched-out holes with an optical
emitter shining through the holes on one side and a detector on the
other working against a crystal time base. An early PLL.

Oh well, just reminiscing...

 

[[email protected]]

---
Which generally manifests itself as provocation = disagreement.
---


---
Which is about the double standard you exact. If, in fact, your
posts are made without rancor, which is ridiculous on its face, you
insist that what must then be "carelessness" on your part be not
interpreted as insult, but that infinite care be taken with
correspondence directed to you in order that you not interpret it as
insult.
---

Of course, if you could find an example where I was unreasonably easily
provoked, or "accidentally" produced a grievous insult, you'd quote it,
thus converting a pointless troll into something worth reading.

If you say so John - since you don't know my wife or her colleagues,
you are free to let your imagination run wild. Pity you haven't got an
imagination that can usefully exploit this lack of factual restraint,
let alone any more modern electronic component than the 555.

 

[Robert Baer]

Oops, I forgot the extra divider gates needed. Perhaps the 74HCT40104
as someone else mentioned might be better...
Either way you need a 10.752MHz oscillator and some form of 15 stage
divider.

Space-wise I still think a small 8pin microcontroller is a better
solution. Do you need 50-50 duty cycle?, if so you'll need an extra D
flip-flop on on the output.

Dave

..do it in software..

 

[Robert Baer]

Jim Thompson wrote:

On Mon, 04 Dec 2006 00:03:56 GMT, Robert Baer



Jim Thompson wrote:


On Sun, 03 Dec 2006 19:19:05 GMT, Robert Baer

[snip]

That ratio is temperature sensitive...


What "ratio" is that?

...Jim Thompson

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


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

I suggest that you do some measuring...

I suggest you get you head out of your ass. I've been designing IC's
since the beginning of time... ratiometric is what it's all about.

...Jim Thompson

Do tell; that is ASS-u-ME-ing that the ratios are *constant*.

 

[Jim Thompson]

Jim Thompson wrote:


On Mon, 04 Dec 2006 00:03:56 GMT, Robert Baer



Jim Thompson wrote:


On Sun, 03 Dec 2006 19:19:05 GMT, Robert Baer

[snip]

That ratio is temperature sensitive...


What "ratio" is that?

...Jim Thompson

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


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

I suggest that you do some measuring...

I suggest you get you head out of your ass. I've been designing IC's
since the beginning of time... ratiometric is what it's all about.

...Jim Thompson

Do tell; that is ASS-u-ME-ing that the ratios are *constant*.

Who do you think you are, Eeyore or some similarly IGNORANT person?

Please explain on me how the ratios are not. (Assuming you have even
the vaguest clue about resistor TYPES.)

...Jim Thompson

 

[John Fields]

Of course, if you could find an example where I was unreasonably easily
provoked, or "accidentally" produced a grievous insult, you'd quote it,
thus converting a pointless troll into something worth reading.

---
Just because I can't be bothered to slog through the morass of your
posting history in order to find an example of your nasty attitude
certainly doesn't mean there aren't thousands of examples out there.
---

If you say so John - since you don't know my wife or her colleagues,
you are free to let your imagination run wild. Pity you haven't got an
imagination that can usefully exploit this lack of factual restraint,
let alone any more modern electronic component than the 555.

---
It's true that I don't know them, but knowing _you_ is enough to
know how they'd behave if they were nice people who had to but up
with an overbearing know-it-all like you.

I'm working on a project right now where I'm using an MC68HC908JL8.
And you?

Still hanging on to that pig-ignorant belief that a 555 is a "bad"
chip which no one should use because you won't? Even when it's the
perfect candidate for the job?

 

[Robert Baer]

Jim Thompson wrote:

On Mon, 04 Dec 2006 05:27:34 GMT, Robert Baer



Jim Thompson wrote:



On Mon, 04 Dec 2006 00:03:56 GMT, Robert Baer




Jim Thompson wrote:



On Sun, 03 Dec 2006 19:19:05 GMT, Robert Baer


[snip]


That ratio is temperature sensitive...


What "ratio" is that?

...Jim Thompson

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


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

I suggest that you do some measuring...


I suggest you get you head out of your ass. I've been designing IC's
since the beginning of time... ratiometric is what it's all about.

...Jim Thompson

Do tell; that is ASS-u-ME-ing that the ratios are *constant*.

Who do you think you are, Eeyore or some similarly IGNORANT person?

Please explain on me how the ratios are not. (Assuming you have even
the vaguest clue about resistor TYPES.)

...Jim Thompson

Sounds like you may need an education in electronics...

 

[Jim Thompson]

Jim Thompson wrote:
[snip]

Who do you think you are, Eeyore or some similarly IGNORANT person?

Please explain on me how the ratios are not. (Assuming you have even
the vaguest clue about resistor TYPES.)

...Jim Thompson

Sounds like you may need an education in electronics...

Sounds like you need a PLONK ;-)

...Jim Thompson

 

[David L. Jones]

Jim Thompson wrote:
[snip]

Do tell; that is ASS-u-ME-ing that the ratios are *constant*.


Who do you think you are, Eeyore or some similarly IGNORANT person?

Please explain on me how the ratios are not. (Assuming you have even
the vaguest clue about resistor TYPES.)

...Jim Thompson

Sounds like you may need an education in electronics...

Sounds like you need a PLONK ;-)

I wonder how many of your IC's Robert has used and didn't even know it?
;-)

Dave

 

[[email protected]]

---
Just because I can't be bothered to slog through the morass of your
posting history in order to find an example of your nasty attitude
certainly doesn't mean there aren't thousands of examples out there.
---

Your search skills aren't exactly impressive, but the intelligent
reader will still conclude that there are many fewer than thousands of
examples out there, with the likeliest number being zero. Since I seem
only to have cranked out 6520 postings over the past ten years, there
is an upper limit to the examples that you could find.

They are (mostly) nice people, but probably even better-informed in
their subjects than I am in mine - not the sort of company that you
seem to keep, let alone know anything about.

I'm working on a project right now where I'm using an MC68HC908JL8.
And you?

You've got me there. I'm just flat hunting. On the other hand the
MC68HC908 is the 2002 version of Motorola's 8-bit microcontroller,
going back back via the 6805 to the original 6800 from 1975. RISC and
DSP seem to have passed you by.

Still hanging on to that pig-ignorant belief that a 555 is a "bad"
chip which no one should use because you won't? Even when it's the
perfect candidate for the job?

It isn't a "bad" chip, but very rarely an acceptable candidate for any
job in serious electronics these days. There was a thread about this
here a while back, and the concensus was that most professional
electronic engineers don't seem to be using it any more.