Voltage-variable capacitor doesn't work in LTSpice

Thanks, John, that actually seems to work. Beats me why mine didn't because the only difference was that I called "ZZ" "Y" instead.

--
Regards, Joerg 

http://www.analogconsultants.com/

Well, that's what you need an expert for!

It may matter about whitespace in the Q equation; it doesn't seem to like any.

Well, I may find this useful in the future.

--

John Larkin         Highland Technology, Inc 
picosecond timing   precision measurement  

jlarkin att highlandtechnology dott com 
http://www.highlandtechnology.com

Well, energy conservation seems silly... if you are changing C, moving plates around, someone has to provide the energy. And I assume charge or voltage depends on how it's hooked up.

George H.

Win 7 is a royal pain in the you-know-what. I needed a new PC because of simulation speed and they didn't offer XP anymore :-(

Yeah, but now I have to bicycle lots of extra miles to work off the calories.

Thanks. I'll still try that but meantime John's version worked on my PC. It doesn't need any custom symbols. I originally tried it almost the same way but mine produced error messages while John's doesn't.

--
Regards, Joerg 

http://www.analogconsultants.com/

tried right-click "run as administrator" ?

you can put stuff the program directory you just have to copy and say yes to a UAC prompt

-Lasse

Yup :-)

I think I know what it could have been. I had a voltage rail called "X" left in the schematic and it must have not liked that.

--
Regards, Joerg 

http://www.analogconsultants.com/

I did that and then it put it into some extra directory and marked the file with a yellow padlock. I can't stand such behavior of an OS that MS calls "professional".

--
Regards, Joerg 

http://www.analogconsultants.com/

The simulation I posted ala Joerg's transducer demonstrates energy changes (AM modulation) and the FM modulation you'd expect from the capacitor changing value.

I'm musing how to set up an old fashioned "pump" frequency multiplier ;-) ...Jim Thompson

--
| James E.Thompson                                 |    mens     | 
| Analog Innovations                               |     et      | 
| Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    | 
| San Tan Valley, AZ 85142     Skype: skypeanalog  |             | 
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  | 
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I love to cook with wine.     Sometimes I even put it in the food.

Jim, can I assume that your subcircuit switches capacitance between two values based on a voltage? I suspect Joerg's desire is for something that is a mite less "binary".

Which is where I was heading with my question about conservation of charge. Perhaps changing the capacitance breaks something inside the sim related to continuity of charge.

I've seen maybe 10 or 20 examples for sale retail. seen adverts for more.

"change", not "charge"

conservation of matter and all that.

--
umop apisdn

Try this one:

the peak inductor current triples from start to end, so the stored energy in the tank goes up almost 10:1.

--

John Larkin         Highland Technology, Inc 
picosecond timing   laser drivers and controllers 

jlarkin att highlandtechnology dott com 
http://www.highlandtechnology.com

I you make an instantaneous change in C, LT Spice conserves charge, so doesn't conserve energy. Spice doesn't need to conserve energy.

--

John Larkin         Highland Technology, Inc 
picosecond timing   laser drivers and controllers 

jlarkin att highlandtechnology dott com 
http://www.highlandtechnology.com

That probably only works in the cyber world :-)

SPICE has weirdnesses. When I tried to massage the stimulus pulse for the cap values using LC the capacitor action flatlined. The stimulus itself looks ok, it's just that the formula in the cap seems to choke. So I had to restrict it to RC. Beats me why but for now it's good enough.

Thanks again for all the hints. I got it to run and produce a useful WAV output for the software engineer. 60 cardiac cycles. Ba-bump .. ba-bump .. ba-bump .. ba-bump .. ba-bump ............... *BEEEEEEEEEP* .... just kidding ...

--
Regards, Joerg 

http://www.analogconsultants.com/

This is fun:

LTS doesn't mind zero value resistors or caps, but it doesn't like L=0 in this circuit.

--

John Larkin         Highland Technology, Inc 
picosecond timing   precision measurement  

jlarkin att highlandtechnology dott com 
http://www.highlandtechnology.com

[...]

Another method might be to search google for 'heart sounds'. You will find many examples of normal and abnormal sounds to work with. Find a site that allows you to download the file in MP3 format, such as

A normal heart sounds like

Download it and listen in VLC to see if it's what you want. Then search google for MP3 to WAV converters. Watch out for ones that want you to download a 'download management' file. Skip those ones. There's a good online site at

In this case, the normal.mp3 file is 154,227 bytes, and the WAV file is

850,220 bytes. There seems to be some mashup at the beginning, but otherwise it sounds exactly like the MP3 file. You can probably edit it and trim the part you want or extend it.

You can find all kinds of abnormalities to listen to. I have a young and very pretty doctor who just gave me a complete physical. I have absolutely no idea how she can memorize all those different sounds. There are hundreds of them. But maybe you can put them in your device and have them detected automatically.

But it works if you give the inductor 1 femtohenry. Nothing in the world could ever have such a low inductance.

--
Regards, Joerg 

http://www.analogconsultants.com/

The problem is that I need the aortic pressure signal and not the sound. I've mimicked it with an asymmetrical RC sawtooth for now, good enough to test the software initially.

It comes with experience of maybe she has a knack for it. As a kid I was pretty good at diagnosing car engine troubles by ear. Until a kablouie kind of accident in the army messed up my hearing.

Once I told my dad a valve on his new 5-cylinder Audi may be bad, probably an exhaust valve. So he brought it to the dealer. They laughed. "Phhht ... it's brand new and besides, what does a kid know?". My dad insisted. So they did a compression test and sure enough it failed the test on one cylinder. Major engine tear down and its exhaust valve had a deep V-cut burned into it from the side, totally toast. It was a warranty repair.

--
Regards, Joerg 

http://www.analogconsultants.com/

Cool! That signal appears to be much more complex. Good thing you're doing it and not me!