Adding delay to the pulse

--
Why not?  You don\'t have anything better to do, do you?  But then,
you might find that your abhorrence of the part is unfounded and
you\'d have to give up all that precious prejudice you\'ve built up
over the years.  I understand.

--
Guess again.

I\'m just trying to keep it at a level you\'re capable of
understanding.

There's only one way to find out for sure...

Best regards, Spehro Pefhany

--
"it\'s the network..."                          "The Journey is the reward"
speff@interlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com

--
 ;)

All this violence and sex in our society- the Bible warned us about these times....

Yuk!! not while there's dogs in the street.

I very much doubt if you do. I don't have all that much in common with my thirty year younger self, but I don't have any reason to doubt the judgements I made then.

Actually, you are talking about saving money stupidly - worrying about

15 cents on a part when that corresponds to about 11 seconds of design time.

The 4047 is physically larger than the 555 because it offers more inputs and outputs. Since you don't seem to design around anything other than the 555, you may not see this an advantage, but someone whose components choice wasn't trapped in the early 1970's might see more possibilities

Your pathetic grasp of English has tripped you up again. My post made no such "admission". I've mostly worked on high-value low volume equipment, but I've also designed for higher volume production, where every cent counted - for a while I knew exactly what George Kent Limited paid for their regular resistors, their precision resistors and their small signal audio transistors, and adjusted my designs accordingly. The capacitors I had to look up. and at that time the integrated circuit prices were changing fast enough that you had to check them every few days. If I had to I could do it again - it isn't exactly difficult, just inappropriate for low volume and one-off-design, which is what we doing here

--
Bill Sloman, Nijmegen

It's also nasty. The 555 was never a model of stability, and your timings will wander around as room temperature changes and as the supply voltage changes, and will probably also vary with the phases of the moon. You'd better make sure that the weather isn't too humid - the

10M resistor you'd want to use to get the 1 second period isn't going to look like 10M when covered with dew.

You don't have to write code or buy a programmer to buy into this can of worms, but you may wish you had when the customer starts bitching.

These sorts of problems don't seem to get much attention in Texas - ever read a Texas Instrument data sheet carefully? - but can be important out in the real world where people measure stuff.

--
Bill Sloman, Nijmegen

--
You should. There\'s absolutely nothing wrong with a 555 for the
application which was being discussed, and your overriding need to
deny that is telling.

--
So... You don\'t know what the fuck you\'re talking about either!

From Signetics\' original 555 data sheet, for the monostable
configuration drift with temperature is typically 50ppm/C° and drift
with supply is typically 0.1%/V.  Not too shabby, even by today\'s
standards.  The astable is a little worse at 150ppm/C° and 0.3%/V,
but still not as bad as you\'d like to pretend.

As for that 10M resistor, forget it.  With a threshold current of
0.25µA, max, the timing resistor will be limited to 6.8M (per data
sheet) Realistically, since for the 555:


       T = 1.4RC

One would use something in the vicinity of 1µF for the cap, making
the resistor:

              T
       R = ------ ~ 700kR
            1.4C         


But, since it\'s almost always a good idea to use something other
than an electrolytic for timing because of leakage and we\'ve got up
to almost 7 megohms to play with, let\'s say we go for something like
a 0.47µF polyester cap.  Then the resistor will come out to be


                 1s
      R = --------------- ~ 1.5MR
           1.4 * 4.7E-7F

Perfect.

*Typical* drift? *Typical* supply voltage rejection ratio? Do you expect to be taken seriously?

--=20 Bill Sloman, Nijmegen

--
Yes, of course, and if you\'re so intent on _proving_ that the 555 is
such a shitty part then here\'s your chance to get off your ass, find
the data sheet, get the worst case spec\'s and post them.

But will you?  And shoot your own self down?  I think not, LOL!

=3DStarts

Interestingly, that data-sheet includes worst-case specs, while the LM555 data sheet in my National data book doesn't. Nor does the Fairchild datasheet from the web - unsurprising given the history.

The worst case specs aren't impressive - I can see why you didn't bother to post them.

--=20 Bill Sloman, Nijmegen

--- Fairchild's or the 555's?

That URL only points to the first page of 11, (Eleven??? Amazing, for a POS part, no? So many people using them in so many ways and all of them wrong...) but perusing Philips' data sheet (if that's the one you're referring to) shows worst case drift for the one-shot as 150ppm/C° for temp and 0.5%/V for supply rejection and, for the astable, 500ppm for temp and 1%/V for supply rejection.

---

--- Maybe I'm easily impressed, but if I've got a 555 wired as an astable running at, say, 100kHz and my supply dropping from 15V to

14V causes the astable's output frequency to go to 99kHz or, maybe, 101kHz, (I don't want to take the time to figure out which way it goes) I don't think that's horrible. What we're talking about, basically, is a 7% change in the supply causing a 1% change in the output frequency and, if the supply is stable, that change goes into the noise.

The reason I didn't post the worst case specs is because they're not in my Signetics' 1976 data manual and rather than me going hunting for them, I wanted you to do the legwork required to support your position that 555's are trash.

I think your search has proved otherwise. :-)

-- John Fields Professional Circuit Designer

S=3DStarts

Fairchild Semiconductor got taken over by National Semiconductor some years ago, then floated off again as a separate company.

The part itself was designed by Hans Camenzind for Signetics. His book "Designing Analog Chips" - ISBN 978-1-54939-718-7 - devotes the first eight pages of chapter 11 to the 555 and some variants - interesting stuff, but not interesting enough to persuade me to try to use the device.

The Philips data sheet I was looking at is shown as an eight page document - of which the first page is a DataSheetArchive header, leaving a seven page extract from the Philips data book (pages 346-352 inclusive), which isn't unusual for a Philips data sheet.

I would not go so far as to say that evey use of the 555 is per se wrong, but it is reasonable rule of thumb.

I seem to have worked on more demanding systems.

Even Hans Camenzind sees flaws in the original design. The absence of worst case specs gives the manufacturer carte blanch to mess around with the design to minimise the silicon area or to maximise the yield. I really don't like designing around that sort of part, and will go to quite a bit of trouble to replace it with something that is properly specified.

--=20 Bill Sloman, Nijmegen

--
Yes, I know. I worked with Fairchild\'s 100K ECL back in the late
\'70\'s

I didn't get to play with 100k until the early 1980's but on the other hand, I did clean up the beam-steering amplifiers on the first EMBF

10.5 electron-beam microfabricator Cambrdige Instruments sold - to Fairchild Semiconductor, to be used on making masks for 100k ECL.

Whenever I feel the urge to use a 555 coming on, I count up to three - which so far has always given me the time to come up with a better solution.

The 741 has also sold in the millions, not because it is a good part but because loads of people aren't prepared to spend the time learning what is available to do the job better.

--
Bill Sloman, Nijmegen

--
EBMF perhaps?

I\'ve always had a soft spot in my heart for Fairchild.  First with
the goods but, somehow, never able to beat out the competition and
then forced to give away their secrets just to stay alive.

--
EBMF perhaps?

I\'ve always had a soft spot in my heart for Fairchild.  First with
the goods but, somehow, never able to beat out the competition and
then forced to give away their secrets just to stay alive.