Re: How inaccurate is a 555 or 7555 REALLY?


John Fields wrote:
On 5 Dec 2006 21:21:13 -0800, bill.sloman@xxxxxxxx wrote:


Phil Allison wrote:
<bill.slowman@xxxxxxxx>

John Fields:

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.


** Funny how they sell over 1 billion examples each year then, isn't it
????

Not at all. Legacy designs, and land occasional legacy designer, like
John Fields, are an entirely sufficient explanation.

---
Hardly an "occasional" designer, what with designs from, say, 30, or
20, or 10 years ago that are still being manufactured and using up
555's like crazy? Nothing wrong with that, is there?

The designs could be smaller, cheaper, faster and more
current-efficient with more modern designs and components, but
manufacturers are extremely nervous about disrupting an existing
production process. When I - briefly - worked for Chessell Recorders in
the U.K. in 1979, their 100,000-ish per year pen recorder still used a
six-transistor servo amplifier that blew up whenever the pen carriage
stalled. Development had been wanting to replace it with something
cheaper, smaller and stall-proof involving an op amp for years, but
production wouldn' risk any change to their smooth-running production.

Eventually, the Eurotherm board shook up the Chessell management team -
four of us resigned from Chessell's on the same day (purely by
coincidence) and all got to talk to the chairman of the Eurotherm
board. I hadn't been there long enough to say anything interesting, but
others had been there longer ..

Or legacy
designers like me who know how to use a 555 to its best advantage
for many purposes and have no qualms about using it if it's the
device of choice?

Even if a slightly more broadly educated designer might have made
another choice.

Nothing wrong with that either. Especially
since, unlike you, _I'm_ still a working designer. You might also
have noticed that, unlike you, I post actual working designs here
from time to time.

Yes. I've seen them. All very nostalgic. Your recent exercise with a
4024 (the last post in this thread) reminds me of stuff I was doing in
1974 with a 4040, though I didn't decode with three diodes and a
resistor, even back then.

In terms of components, you should have been able to squeeze your
design into a single CMOS 22V10 programmable logic chip. With something
bigger but pin-compatible, like the ICT 7024 PEEL part - which is the
most recent programmable logic part that I've had a chance to play with
- you could proably have also fitted in Arlet's suggestion of dividing
by 79 once in a while to get the average frequency closer to 420Hz, or
divided down from David L. Jones 10.752MHz crystal and got exactly
420Hz.

A more modern programmable logic part - like the Xilinx Coolrunner
series - with in-system programming, 1.8V supply and some really
compact packages - looks as if it would be even nicer, but I've not yet
been able to contrive an excuse to play with one of these parts.

Do you by any chance work for some kind of museum of technology,
exhibiting your skills alongside the guys who make flint arrowheads?

--
Bill Sloman, Nijmegen (but in Sydney at the moment).

.

Relevant Pages

  • Re: How inaccurate is a 555 or 7555 REALLY?
    ... It isn't a "bad" chip, but very rarely an acceptable candidate for any ... Legacy designs, and land occasional legacy designer, like ... John Fields, ... since, unlike you, _I'm_ still a working designer. ...
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  • Re: How inaccurate is a 555 or 7555 REALLY?
    ... It isn't a "bad" chip, but very rarely an acceptable candidate for any ... electronic engineers don't seem to be using it any more. ... It would be interesting to see the shape of the buying curve - the ... selling predominantly into the continueing production of old designs. ...
    (sci.electronics.design)