1 chip 1KHz xtal osc?

[martin griffith]

I read in sci.electronics.design that Reg Edwards

What about components that should be there, but aren't?

Those are extremely reliable



martin

Serious error.
All shortcuts have disappeared.
Screen. Mind. Both are blank.

 

[John Fields]

From my first reply: "I'd use a 74xx4040".

---
Yes, I neglected to notice the family. Mea culpa.
---

Hardly. I see far more systems get to production needing to be
completely re engineered over such null statements than I do because
someone got a chip number wrong. The latter problem shows up _really
early_ in the design process (when someone can't find oscillator pins
and asks, for instance). The former problem can make it all the way out
to the field before the problem is known ("hey, this thing looses a
minute a week!" "you said minimum parts count" "the customer needs a
minute a month!" etc.). Changing a part number before it even hits a
schematic is _way_ easier than a recall, or spending the next 10 years
struggling with unhappy customers.

---
I agree, but my "null statement" was more in line with "The customer
said he wanted plus or minus a minute a week, and that's not
attainable with just two parts, so the lowest parts count we can go
with to attain what he needs is three."
---

The reason is because such heavily qualified statements come from you
assuming that your assumptions are the same as mine. If your
assumptions really are the same as mine then all will be well.

---
I try not to make assumptions, assuming that when I do somehow or
another I'll get bitten.
---

probability the OP just wanted something reasonably close, and the
oscillator in a '4060 would be more than good enough

---
Here's the OP's request:

"I need a lowest possible parts count 1KHz square wave oscillator.

Must use crystal timing with accuracy as good as reasonably attainable
without use of oven.."

 

[Don Pearce]

Reliability is Quality versus Time.

ALL components MUST serve a recognisable purpose.

Any redundancy MUST be deliberately introduced and NOT have found its way
into the circuit by chance.

If a designer is unable to describe the purpose of each and every component
then he himself should be made redundant.

You have to watch out which reliability criteria you use. WHen I was
designing signal generators for Marconi we used Milstress. It gave a
rather amusing result that the reliability was supposedly much higher
without a cooling fan.

Go figure.

d
Pearce Consulting
http://www.pearce.uk.com

 

[John Fields]

Putting my marketing hat on for the moment (and not reading data sheets
_again_):

100ppm should be quite achievable with a crystal oscillator. So if you
have a 10MHz oscillator that's a 1kHz error, right?

10MHz ± 1000000ppm = ±100% = ± 10MHz
10MHz ± 100000ppm = ± 10% = ± 1MHz
10MHz ± 10000ppm = ± 1% = ± 100kHz
10MHz ± 1000ppm = ±0.1% = ± 10kHz
10MHz ± 100ppm = ±0.01% = ± 1kHz

Right.

Now if you have a 1kHz oscillator with 1.5% accuracy, that's only 15Hz,
right?

And 15Hz is _much_ smaller than 1kHz, right?

So they are getting better than crystal accuracy!

Wrong, but understandable if you're wearing a marketeer's hat!^)

1kHz ± 100ppm = 1kHz ± 0.01%, therefore 1kHz ± 1.5% is 150 times worse
than crystal accuracy!

 

[John Woodgate]

I read in sci.electronics.design that John Fields <jfields@austininstrum

I agree, but my "null statement" was more in line with "The customer
said he wanted plus or minus a minute a week, and that's not
attainable with just two parts, so the lowest parts count we can go
with to attain what he needs is three."

That doesn't present too much of a problem. A problem is when the second
half of the sentence has '500' instead of 'three'. (;-)

 

[John Woodgate]

I read in sci.electronics.design that Don Pearce <[email protected]>

You have to watch out which reliability criteria you use. WHen I was
designing signal generators for Marconi we used Milstress. It gave a
rather amusing result that the reliability was supposedly much higher
without a cooling fan.

Would you like my TF2002 as a souvenir? I gave up trying to repair it
when I found the eighth case of degraded insulation having eroded the
wire away.

 

[Ben Bradley]

I need a lowest possible parts count 1KHz square wave oscillator.

[this is like a game show "Design That Circuit" in the spirit of
"Name That Tune"] I can do that with an op-amp, a capacitor and three
resistors.

Must use crystal timing with accuracy as good as reasonably attainable
without use of oven..

Oh, well that's different...
That would be a temperature-compensated crystal oscillator (TCXO).
Dallas makes one that oscillates at 32.768kHz, in fact that's almost
the part number.

To do this, I assume it is best to start with the highest frequency
crystal possible, as each divide down increases resolution.

No it doesn't, if the crystal changes frequency, the divided down
signal changes frequency by the same percentage. Higher frequency
crystals are pretty much as stable, or unstable, as lower frequency
ones.

Power requirements are open.

Can anyone please advise regarding the most suitable circuit design?

Do you need exactly 1kHz, or would a very stable signal at 1024Hz
or 992.9696...Hz? If either of those would work, you can use the
Dallas part and a 4024 to divide the oscillator output by 32 or 33.
If you need exactly 1kHz, there are plenty of other TCXO's at
higher frequencies that will divide down to exactly 1kHz.

 

[Tim Shoppa]

---
If your crystal is specified to perform to some level of accuracy
under some set of conditions, then regardless of the crystal frequency
or the number of divisions you do, the accuracy of the derived
frequency will be the same as that of the crystal, neglecting
artifacts introduced by the dividers.

At the same time, some crystals (like 32.768kHz) are manufactured by
the billions, are really cheap (like a dime), and have specs of better
then 20ppm at 25 C.

And different cuts are possible at different frequencies. He said
he doesn't want an oven but wants some undefined accuracy. Choosing a
cut that works well over his (unspecified) temperature range may limit
the available frequencies. (And may rule out 32.768kHz tuning fork crystals).

32kHz crystals aren't quite as cheap as 32.768kHz but they are cheap
and widely available and the division to 1kHz is trivially easy.

Tim.

 

[Don Pearce]

I read in sci.electronics.design that Don Pearce <[email protected]>


Would you like my TF2002 as a souvenir? I gave up trying to repair it
when I found the eighth case of degraded insulation having eroded the
wire away.

Oops! - a bit pre-me, that one. My designs were the 2031/ 2041
gennies.

d
Pearce Consulting
http://www.pearce.uk.com

 

[John Fields]

32kHz crystals aren't quite as cheap as 32.768kHz but they are cheap
and widely available and the division to 1kHz is trivially easy.

 

[Paul Burridge]

Reliability is Quality versus Time.

ALL components MUST serve a recognisable purpose.

Any redundancy MUST be deliberately introduced and NOT have found its way
into the circuit by chance.

If a designer is unable to describe the purpose of each and every component
then he himself should be made redundant.

Do you smoke, Reg?

 

[CFoley1064]

Subject: 1 chip 1KHz xtal osc?

From: Mark Roberts [email protected]
Date: 7/8/2004 8:35 PM Central Daylight Time
Message-id: <[email protected]>

I need a lowest possible parts count 1KHz square wave oscillator.

Must use crystal timing with accuracy as good as reasonably attainable
without use of oven..

To do this, I assume it is best to start with the highest frequency
crystal possible, as each divide down increases resolution.

Power requirements are open.

Can anyone please advise regarding the most suitable circuit design?

With appreciation,

Mark

3 parts?

1KHz Crystal-Based Oscillator VCC
+
VCC 16|
+ .---o----------------------.
Vcc|4 | Vcc |
.-----o------. | |
| | | |
O/E| 2.048 MHz |Out 10| |

----o Oscillator o------oCLK HC4040 |

Control 1| |3 | |
Signal | GND | | |
'-----o------' | |
2| | |
=== | GND RST /2^11 |
GND '---o-----o----------o-----'
8| 11| 15|
=== === |
GND GND |
|
^
1KHz Out

created by Andy´s ASCII-Circuit v1.24.140803 Beta www.tech-chat.de

crystal oscillator: Crystek C3391-2.048 (25ppm stability over temp range of 0
- 70 deg. C, Mouser P/N 549-C3391-2.048)
@ 2.64 USD ea. qty 1

IC: Fairchild MM74HC4040M (SOIC-14 SMT) Mouser P/N 512-MM74HC4040M, $0.43 ea.
qty 1

The third part is an 0.1uF bypass cap across the oscillator power supply.

Use a 5VDC power supply. Use a smaller IC if you want. Would you like fries
with that?

Good luck
Chris

 

[John Fields]

I read in sci.electronics.design that John Fields <jfields@austininstrum


That doesn't present too much of a problem. A problem is when the second
half of the sentence has '500' instead of 'three'. (;-)

 

[John Woodgate]

I read in sci.electronics.design that John Fields <[email protected]>

Good to see you back; where ya been?

Too busy; newsgroups were taking up too many hours, and during May I was
travelling in Europe a great deal. I came back to ask for help with the
SMPS mains harmonics problem.

 

[David L. Jones]

Why not a PIC10F clocked with a 32KHz crystal and 10 lines of assembly code
? A sub-1$ solution...

How do you get an accurate 1KHz from a 32.768KHz crystal?
It requires a division ratio of 32.768
Or if you actually mean a 32.000KHz crystal, then where are they readily available?

Dave

 

[David L. Jones]

The Epson SPG6851 is a true single chip solution with NO external
components required (it's a programmbale oscillator). BUT it is
offically discontinued according to Epson, so is not recommended for
new designs. But you can still buy it at Farnell (300-3097) and other
places.
Tempco ain't that great though.

There may be other programmable oscillators around, but I don't know
any off-hand that will do 1KHz.

Regards
Dave

Correction. Tempco of that model is 5ppm - fantastic.
Guess that's why it's so expensive.

Dave

 

[Robert Lacoste]

How do you get an accurate 1KHz from a 32.768KHz crystal?
It requires a division ratio of 32.768
Or if you actually mean a 32.000KHz crystal, then where are they readily

available?

Yeah, agreed, I clicked on "send" too quickly, my apologizes.
Say a pic 16F and a 4/8/10/12MHz crystal (still close to $1, no ?) ;+)

Friendly,
Robert

 

[Tim Shoppa]

You have to watch out which reliability criteria you use. WHen I was
designing signal generators for Marconi we used Milstress. It gave a
rather amusing result that the reliability was supposedly much higher
without a cooling fan.

Go figure.

Easy: the cooling fan was the least reliable component .

Of course, profit (especially for a government contractor) is usually
inversely proportional to reliability!

Tim.

 

[Fred Bloggs]

You have to watch out which reliability criteria you use. WHen I was
designing signal generators for Marconi we used Milstress. It gave a
rather amusing result that the reliability was supposedly much higher
without a cooling fan.

Go figure.

That would be easy to figure, you did not allow MILSTRESS to update the
elevated temperature failure rate acceleration factors with fan removed,
which should have made it less reliable than the fan-cooled system. It's
all the same anyway, now that a gazillion device-hours of data are
available, it has been found that there is nowhere near the improvement
in lifetime of modern devices from reduced Tj as predicted.

 

[John Fields]

How do you get an accurate 1KHz from a 32.768KHz crystal?
It requires a division ratio of 32.768
Or if you actually mean a 32.000KHz crystal, then where are they readily available?