From: Terry Pinnell
Subject: Re: Flash a string of LEDs
Date: Thu, 05 Dec 2002 13:53:44 +0000
References: <firstname.lastname@example.org> <email@example.com>
NNTP-Posting-Date: Thu, 5 Dec 2002 13:54:06 +0000 (UTC)
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"fred bartoli" wrote:
>Yes, the same. I've just set the cap value to 22uF as I recall something
>like that from an earlier exchange between you and Spehro. However it should
>not change anything about the behaviour, except the flash period of course.
>The simulation time is set to 10 seconds.
>The time step has nothing to do with simulation.
Not sure I understand that, Fred? If I accept the defaults that CM
offers, of 5 uS and 20 nS for step and stop respectively, then I
obviously won't see much! As with most of my sims, I have to set it
manually. In this case (having reduced cap to 22 uF) I chose a stop
time of 10 S and a step time of 10 mS. These have a very significant
effect on whether I see the result in a second or two, or a few days
But, apart from the *display* (which is maybe what you meant?),
doesn't the step value also affect simulation itself? I frequently get
'timestep too small' or some such message. And I'm pretty sure I
recall changing this value has sometimes got an oscillator simulating
(or stopped it).
>It has effects after the
>simulation is done and gives the sampling period of the raw datas, *after*
>the simulation is done, for the ascii output file. I don't know about CM but
>I guess almost all todays spices don't use this file as the interface with
>the scope program as this leads to lots of artifacts problems
>(undersampling...). So if CM directly use raw data, simply set TimeStep to a
>reasonably low value (don't generate huge text files) and all should be OK.
>You can test this by setting a simple simulation file with a sine wave and
>running 2 sims varying the timestep parameter and looking at what you have
>in your scope.
>For your simulation still not working don't forget that the oscillator, as
>all, has a start up time (in my case with 22uF it's about 5 seconds), so let
>enough simulation time.
>Hmmm, wait a minute...
>Ok, that's it. I've set the cap to 220 uF. It also refuse to start and
>instead gently settle to the DC bias point I obtain without using the UIC
>Now build an AC analysis to measure the circuit loop gain (there was a
>recent thread about this but I can't remember what it was). Then vary the
>cap and see what happens to your loop gain.
>In my case with a 22uF cap the loop gain goes above 0dB somewhere -> the
>When setting the cap to 220uF the loop gain *never* go above 0dB -> no
>Then I set the 1uF cap to 10uF, the loop gain rise again above 0dB somewhere
>and the circuit starts again.
>Setting back to 220uF/1uF but increasing the 220R value to 1K, the loop gain
>rise again above 0dB somewhere and the circuit still starts.
Thanks for taking the trouble, Fred. It's made me even more determined
to get it working (especially as it works so well on breadboard, even
with 220 uF). But as you see from
it still eludes me!
Hobbyist, West Sussex, UK