More on dual pulse generator

[Jag Man]

Whether it's a nuisance to _you_ is of no consequence when you're the
one asking for help.

Actually, I was thinking of it from the perspective of any reader, not just
me. Since
e-mail tools usually have a the ability to coordinate threads anyone needing
the
history can easily read the prior messages, in which case only two things
are
important: the new comment and what, specifically, is being responded to.
I can't imagine anyone wanting to hit the page down key
5 or 6 times to see what new is being added, unless of course threading
is not being handled by the mail tool. Other mail lists and
newsgroups I participate in have rules prohibiting excessive
quoting, as it unnecessarily clutters the archives. So one is encouraged to
edit out all but the cogent part
of the previous message and then insert the new material, either before,
inline, or after
the quoted part. But, I have already conceded the point, and am willing
to conform to local rules. The info is what I'm after, and have no wish to
iritate anyone.

Guess the problem I have there is translating what I read there into
something actionable.
In this case, which datasheet limit should I use to set resistances for
acceptable current?

---
Maximum currents into the trigger and threshold inputs.
---

How would one calculate these two values from circuit parameters in order to
have something to compare to the spec sheet values?

I know that my main problem is the transistor was still new technology
and
the IC was
still 15 years away when I took my circuits class... IOW, I'm and
interloper
here! Thanks
for your patience.

---
You're not an interloper. This is, after all, sci.electronics.basic,
but you do seem to have an attitude.

None intended. Maybe I go back over my posting and see if I could have
put something differently.

Anyway, my little box seems to be working well enough to use now, so
maybe
wait a while
before going back and changing all those resistors and caps.

---
Hey, if it works, don't fix it!

Hope it does. If so, it will be because of help form you and other members
of this
group.

Ed

 

[Terry Pinnell]

Robert Monsen <rcsurname@comcast.net> wrote:

Jag Man wrote:
I took the IC components back to the breadboard so I could make changes
easier.
When I changed the input harness to the trirgering 555, multiplying all
resistors by 100
and dividing the capacitor by 100 the power rail voltage became clean.
However,
the bad behavior continued.

<snip>

(You really need to start bottom posting. Thats the convention here, and
it makes it easier for everybody to read the replies)

Could you also do something about your word-wrap setting please. I see
all your posts like the fragment above. No amount of adjustment here
(in Agent) corrects them.

From OE Help
To set the line length in outgoing newsgroup messages
-----------------------------------------------------

Outlook Express automatically sets the line length of messages using
plain text format at 76 characters per line. This accommodates news
servers that do not display more than 80 characters per line. When
messages are quoted in a reply, the original text is usually marked
and indented with an additional character. If your message is likely
to be quoted after posting, set your text to wrap at 70 or 72
characters per line to prevent text from running beyond the edge of
the window.

On the Tools menu, click Options.
On the Send tab, in the News Sending Format section, select Plain
Text, and then click the Plain Text Settings button.
In the text box for Automatically wrap text at x characters when
sending, type the number of characters you want displayed per line.

--
Terry Pinnell
Hobbyist, West Sussex, UK

 

[John Fields]

On Wed, 08 Dec 2004 04:14:43 GMT, "Jag Man"
<Jag_Man653R-E-MOVE@hotmail.com> wrote:

Guess the problem I have there is translating what I read there into
something actionable.
In this case, which datasheet limit should I use to set resistances for
acceptable current?

---
Maximum currents into the trigger and threshold inputs.
---

How would one calculate these two values from circuit parameters in order to
have something to compare to the spec sheet values?

---

In the original NE555, the TRIGGER input is the base of a bipolar PNP
transistor which sources current, and the THRESHOLD input is the base
of an NPN which sinks current WRT GROUND.

Signetics spec's the trigger current at 2ľA typical and the threshold
current at 250nA max so, when the 555 is cofigured as a monostable,
the timing resistor must supply the input current to the 555 as well
as the current required to charge the timing cap. The current
required to charge the cap includes the leakage current of the cap,
which can be considered to be a resistor in parallel with the cap, so
the timing resistor needs to be chosen to allow the voltage at the TH
terminal to rise to 2/3Vcc while supplying the current to charge the
cap, the leakage current for the cap, and the input current to the TH
input.

When configured as an astable a similar situation will arise, but the
current being sourced by the TRIGGER needs to be considered.

For most applications, however, the easy way out is to just slap
something in there and see if it works...

--
John Fields

 

[Jag Man]

How would one calculate these two values from circuit parameters in
order to
have something to compare to the spec sheet values?

---

In the original NE555, the TRIGGER input is the base of a bipolar
PNP
transistor which sources current, and the THRESHOLD input is the
base
of an NPN which sinks current WRT GROUND.

Signetics spec's the trigger current at 2ľA typical and the
threshold
current at 250nA max so, when the 555 is cofigured as a monostable,
the timing resistor must supply the input current to the 555 as well
as the current required to charge the timing cap. The current
required to charge the cap includes the leakage current of the cap,
which can be considered to be a resistor in parallel with the cap,
so
the timing resistor needs to be chosen to allow the voltage at the
TH
terminal to rise to 2/3Vcc while supplying the current to charge the
cap, the leakage current for the cap, and the input current to the
TH
input.

Well, I asked! Thanks, John.

When configured as an astable a similar situation will arise, but
the
current being sourced by the TRIGGER needs to be considered.

For most applications, however, the easy way out is to just slap
something in there and see if it works...

Tell me, do SPICE and similar programs typically have models of
the generic 555 that are good enough for desigh calcs like this?


Ed

 

[Rich Grise]

On Tue, 07 Dec 2004 21:51:59 -0600, John Fields wrote:

On Tue, 07 Dec 2004 22:36:03 GMT, "Jag Man"
Jag_Man653R-E-MOVE@hotmail.com> wrote:



(You really need to start bottom posting. Thats the convention here, and
it makes it easier for everybody to read the replies)

I noticed that, but to me it's a nuisance to have to skip down through
several pages of
history to see what's new. But, when in Rome...

---
Whether it's a nuisance to _you_ is of no consequence when you're the
one asking for help.

Yes, and it could be a nuisance to decide whether to say, "So-ji ma-la!"
or "Don't shoot!"

i.e., it behooves the asker to use the language of the askee.

Thanks,
Rich