More on dual pulse generator

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...

I was using m for Micro, having no "mu" on my keyboard. I do know the difference.

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? 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.

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. I shouldn't have been in such a hurry to pick up the soldering iron. and

Ed

I know, I wasn't doubting that. However, typing mF means 1e-3F, so it was confusing for me. Instead of mu, I use u, as in uF. That seems to be unambiguous.

Well, there doesn't seem to be one. (I have 4 different variants, and I can't find any advice except the LM555 from national, which states that the sum of Ra and Rb should be less than 20M).

Good luck with it.

--
Regards,
   Robert Monsen

"Your Highness, I have no need of this hypothesis."
     - Pierre Laplace (1749-1827), to Napoleon,
        on why his works on celestial mechanics make no mention of God.

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.

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

and

interloper

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

maybe

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

Ed

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

---

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 2µA 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

order to

PNP

base

threshold

so

TH

TH

Well, I asked! Thanks, John.

the

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

Ed

Yes.

--
Terry Pinnell
Hobbyist, West Sussex, UK