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'[EE]: SPICE and Simulators'
2001\01\02@105849 by Lawrence Lile

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In order to keep the flame wars about schematic editors going, I'd like to
discuss simulators.  I just ran across a simulator called Visual Spice.  The
price is reasonable, it looks like a professional package, and I'm checking
out a demo.  http://www.islandlogix.com/   Anybody used it?

I've been using a simulator/layout editor from Visionics called EDwin.  It
is a crude DOS port, crashes a lot, and refuses to simulate anything with an
Opamp in it, or anything very complex at all.  I'd gladly retire it, when I
get something better.


I've heard bad stuff about Electronics Workbench, although the demo looked
good last time I tried it out ( > 2 years ago)

I'm using Eagle as my layout package, and it doesn't come with any
simulator.  I've got plenty of access to free SPICE programs, with their
crude text interface that drives me nuts.  I think I've learned it and
forgot how to use text SPICE twice already.  I would rather pay good money
for a graphical schematic capture front-end, thank you.

Any recomendations?

-- Lawrence Lile
Sr. Project Engineer
Salton inc. Toastmaster Div.
573-446-5661 Voice
573-446-5676 Fax

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2001\01\02@112214 by David VanHorn

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I've had mixed results with simulation, mostly because they never include
ALL the details of the circuit.  I tend to simulate in hardware :)

BTW, how did the smoke detector work out?

I was thinking on that some more.. Your target is a little unusual, and a
reflective detector may not work.. If I understand it right, your target is
carbon soot, which absorbs IR very well.

Might work better, to set up a feedback loop that requires a certain level
of illumination on a phototransistor, and monitor LED drive current.

You could do both methods in the cruciform box arraingement.

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Where's dave? http://www.findu.com/cgi-bin/find.cgi?kc6ete-9

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2001\01\02@120437 by Lawrence Lile

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Dave pontificated:

> I've had mixed results with simulation, mostly because they never include
> ALL the details of the circuit.  I tend to simulate in hardware :)

I am usually trying to simulate just one aspect of the circuit.  For
instance, I've used simulators a lot to predict power usage in power supply
components, modeling he rest of the circuit as a big resistor.  Sometimes
this is not a trivial calculation.   I've used simulation to help work out
bias resistors in transistor circuits, instead of doing them the hard way.
Calculating parameters in circuits that are hard to measure in a real
prototype is another good use.  Simulation can often account for subtleties
that I'd ignore in hand calculations.   When it works, simulation is easier
and faster than breaking out the old handbooks or cooking up a crazy test
and measurement fixture.

One of the best simulator uses I had was modeling a rather tricky, but
simple analog circuit that had all sorts of temperature dependant parts.
Since it was a timer that was supposed to change it's timing in response to
temperature, using  timing capacitors that leak at high temperatures, SCR's
that change trip points at high temperatures, temperature dependant
resistors and so on, a simulator was the way to go when designing it.  I am
sure there are people who go a whole career without a simulator, it's not an
absolutely essential tool.  It's just real handy when things get
complicated.


I _never_ rely on simulation alone.  Like Ciarcia, my faith is in solder,
not sophistry.

--Lawrence Lile

"My favorite programming language is solder"  - Steve Ciarcia

{Original Message removed}

2001\01\02@123343 by Herbert Graf

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Try SuperSpice http://www.anasoft.co.uk/, I haven't used it much but it
looks very promising. TTYL

{Quote hidden}

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2001\01\02@124136 by Alan B. Pearce

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>I've heard bad stuff about Electronics Workbench, although the demo looked
>good last time I tried it out ( > 2 years ago)

My experience with EW has not been good. I used version 5.12 and found it
somewhat frustrating. One circuit I tried to simulate for a switch on delay
would not simulate apparently because the RC network was very early in the
netlist. Another circuit had a 74HC194 parallel to serial shift register that
just would not simulate properly. I do not know where they got the library from,
but I ended up getting a data book out and building the equivalent circuit as
given by a chip manufacturer and this simulated correctly.

Another problem is do not expect the connections on your circuit diagram to stay
in position once you place them. They rubber banding will snap in (slight pun)
and move them to where you dont want them just at a critical time when you are
trying to adjust something when time is critical. This sometimes results in the
lines being on top of others on the display in which case one turns off the
other, and you can have strange looking connections that do not actually exist.

To get the logic analyser tool to sample the waveforms correctly I had to have
an oscillator at twice the clock frequency of the circuit and include a
flip-flop to divide it by 2 to operate my circuit. The sample times of the logic
analyzer are related to the maximum clock frequency being used in the circuit,
you cannot sample at higher than the actual circuit frequency. My other
complaint with it is there is no way to label the traces with signal names to
show someone on a printout or documentation purposes.

On the other hand some of the tools are nice, like the LED you attach to a
signal line (without requiring a ground) to see the state. Makes a nice digital
probe.

When I did get it working it did give me reasonable results that allowed me to
build the required circuit, but it did produce a lot of frustration along the
way. Some of this may have been my fault as it was my first use of a spice tool,
but it was not a pleasant introduction.

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2001\01\02@152255 by Lawrence Lile

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I checked out SuperSpice a while ago.  Although the picture of the author
did not give me any confidence in his programming skills (looks rather like
a Death rocker to me)  his program seemed to be all there, unlike his morals
or his hairstylist.

Unfortunately it tended to crash rather early on in the simulation, and I
decided it wasn't for me.  I was worried about his depth of staff and
customer support, being only one guy, and prone to wierdness besides.   But
why not support those independant programmers?  That's what a lot of us want
to be isn't it?

So far Visual Spice is interesting.  It is a very bare visual layer on top
of a very hairy implementation of Spice - it looks like you really need to
understand Spice itself to use it (which is what I wanted to avoid...)
OTOH it is probably quite powerful (the usual tradeoff between power and
learning curve..)

For $99 to $299 US depending on version, it looks like a good deal.

-- Lawrence


{Original Message removed}

2001\01\02@164252 by steve

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> I am usually trying to simulate just one aspect of the circuit.  For
> instance, I've used simulators a lot to predict power usage in power supply
> components, modeling he rest of the circuit as a big resistor.

I've just pulled Switcher CAD 3 off Linear Tech's website. So far I'm
really impressed with it. It's very quick to cobble a circuit
together with real components (eg. Select an AVX 10uF, 16V Tant and
get all the parameters).
Generally I use the simulator as a second opinion/peer review and
this would be really good for that.

Steve.
======================================================
Steve Baldwin                Electronic Product Design
TLA Microsystems Ltd         Microcontroller Specialists
PO Box 15-680, New Lynn      http://www.tla.co.nz
Auckland, New Zealand        ph  +64 9 820-2221
email: spam_OUTstevebTakeThisOuTspamtla.co.nz      fax +64 9 820-1929
======================================================

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