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Components and Circuits For discussions about component types, alternatives and availability, circuit configurations and modifications etc. Discussions here should be of a general nature and not about specific sets.

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Old 15th May 2021, 11:45 am   #1
Richardgr
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Default Using LTSpice for schematics

There are times when it is necessary to draw a schematic, in my case to help with the understanding of the circuit, and I have been looking at the tools available. The traditional tool is the back of an unfolded cigarette packet, but they are not so easy to come by these days. The best tool of all is Microsoft Visio for non-professionals, but that has quite a steep learning curve and is expensive.

There are other tools like DIYLC, but I have found that LTSpice makes a great tool for schematics, regardless of its abilities to simulate eletronic circuits.

Attached is a view I created of an input stage of a radio. The original hand drawn schema was hard to follow, with missing joins, and could not be uploaded here due to copyright restrictions.

If you look at the schematic, you will see a heptode and a double diode triode. Those were really easy to create in the symbol editor, and then are added to the symbol library for future use. Now, you could go the whole distance and create a mathematical model for simulating a heptode, but for schematics it is not necessary.

The symbols snap to the grid, and connections snap to the connections on the symbols. The symbols can be duplicated, cut, moved and dragged.

LTSpice is free and can be found here: Analog Devices - LT Spice
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Old 15th May 2021, 12:18 pm   #2
kalee20
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Default Re: Using LTSpice for schematics

Very good work! I'm impressed, it's a good engineering diagram.

It's not the best schematic package I've come across - I prefer PADS - but LTSpice does then give you the ability to simulate the circuit. (Which is its primary purpose, of course).

So - give us a clue - you're clearly LTSpice-fluent, how long did it take to draw this?
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Old 15th May 2021, 1:12 pm   #3
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Default Re: Using LTSpice for schematics

I like LTspice, saves a lot of blowing up! There is one major downside, you can spend hours having fun! There are all sorts of additional components (like the valves you have used) available with the simulation constants included.
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Old 15th May 2021, 1:37 pm   #4
Richardgr
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Default Re: Using LTSpice for schematics

I guess there's a few hours there. Dragging is not as easy as in Visio, for example, so initial placement counts. The bit I discovered that I really liked was the tool for creating symbols. I created the variable caps, extra tubes, and then on another diagram I had ganged switches.
It was fun and kept me off the streets, and away from high voltages ;-)
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Old 15th May 2021, 1:44 pm   #5
paulsherwin
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Default Re: Using LTSpice for schematics

I don't find LTSpice particularly easy to use either for drawing or simulation, but then I don't spend enough time using it to become proficient.

For anyone interested, the Windows version runs well under Linux using Wine.
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Old 15th May 2021, 2:19 pm   #6
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Default Re: Using LTSpice for schematics

I wouldn't recommend the Mac version of LTspice, the human interface is remarkably pedantic and very tightly structured. It needs LOTS of right clicks to get pull down menus, which on a laptop means doing CTRL-Click simultaneously. It'll have you trying to eat the carpet! In this respect it is not at all like the PC version.

I've used LTspice for a long time and made some huge simulations of RF stuff and LF stuff controlling it. It works really well. Learning your way around it is not easy, nor is it particularly difficult. It is rewarding, however.

It looks intimidating to start with, but it's worth persevering with. It isn't crippleware, it isn't an amateur toy. It's the full-blooded real thing. You need to learn how to avoid all the fancy stuff at first and just use it as a basic tool. THis will get you going. But once you've got a bit up the learning curve, the fancy stuff is there, waiting for you when you want to use it.

The other approach is to get and use a beginner's toy simulator and learn on it. You soon find its limitations and need something grander. So you get a better simulator and start learning all over again.... until you hit its limitations and go buy something more comprehensive and start it from scratch.

Going for a full-blooded thing used to be expensive. Linear Technologies really blew the doors off that one. LTspice is free and fully the equal of many expensive professional packages. The remaining drawback is that it looks intimidating. But, a bit of 1 on 1 tuition to get you going easily overcomes the shakes. You can then learn at your own pace. I don't think any one person really knows the whole thing, but a very large number of people know enough for their own requirements.

The circuit drawing package is a bit stylised to suit simulation, but all circuit drawing packages are stylised one way or another. No computer drawing package touches the versatility and instinctive interface of a pencil :=)

David
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Old 15th May 2021, 2:33 pm   #7
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Default Re: Using LTSpice for schematics

I've been using LTSpice quite a bit lately (a few weeks only), not so much for drawing schematics, as to improve my understanding of solid state amps, and how they function / perform in detail, as well as to learn the use of the program itself.

It's been very educational using the published schematics and spec. of a NAD 3020, to draw and simulate parts of the circuit (most) in LTSpice. Not all the components exist within the basic LTSpice library, so I've been 'forced' to learn how to build the symbols and schematics needed for e.g., linear, inv. log, and tapped potentiometers, as I went along, as well as finding and adding the specific component 'models' for various transistors, etc. Simulation of RIIA networks was also somewhat of a 'hurdle' for a while...

In any case, starting from a known schematic and performance spec. I think has helped quite a lot - so it's now at a point where I can simulate a lot of the circuit stages, e.g., to obtain the correct frequency response for the pre-amp, including bass, treble, and tapped volume controls, the transient start-up characteristics of the muting circuit, etc. It's certainly a very useful tool, or will be, albeit one with a not insignificant, but none-the-less enjoyable, learning curve...

It's still very much a work (hobby) in progress, but I'd have to say I've been very impressed with its capabilities so far. I'm not sure I'd recommend it specifically for drawing a circuit but I'm sure I'm still lacking some of the necessary skills...

Alan
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Old 15th May 2021, 2:36 pm   #8
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Default Re: Using LTSpice for schematics

Quote:
Originally Posted by Richardgr View Post
Attached is a view I created of an input stage of a radio. The original hand drawn schema was hard to follow, with missing joins, and could not be uploaded here due to copyright restrictions.
Quite a clear redraw, but not putting B+ line across the top still leaves it harder to follow for Brits.

Aside.... is the UK (and perhaps its previous colonies?) the only place(s) where HT+ (B+) goes at the top, where the power feeds don't have to dive back down to the bottom adding to the tangle of interconnection lines?
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Old 15th May 2021, 3:02 pm   #9
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Default Re: Using LTSpice for schematics

One simple thing in LTSpice is ALT-right-click, it gives the power dissipation. I have used it for a while now and don't even bother with calculating things like roll off frequencies for a simple RC network anymore. Just stick into LTSpice.
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Old 15th May 2021, 3:56 pm   #10
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Default Re: Using LTSpice for schematics

As David says the Mac version of LTSpice has a bizarre user interface. The Windows version isn't that much better but I guess you get used to it, and the core simulation engine is good.

I couldn't really find anything free that supported both Mac, Windows and Linux and had a decent symbol editor for creating your own schematic symbols, so I ended up writing my own (peardrop.co.uk if you're interested) which although still work in progress does most of what I need these days.
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Old 16th May 2021, 6:33 am   #11
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Default Re: Using LTSpice for schematics

I use LT spice for simulations, it takes a bit of getting used to but is very powerful.
I had a need to do a tolerance analysis on a simple circuit to prove that it would meet the required spec under any combination of values within the specified tolerances of the individual components. That's when I discovered that LT spice has some added features not in the manual like, Monte Carlo analysis which did exaclty what I wanted.

However to draw a neat schematic I use Splan7 especially if it is to be published.

Peter
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Old 16th May 2021, 1:14 pm   #12
AndyWright
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Default Re: Using LTSpice for schematics

I use LTSpice for simulations, but for drawing schematics I prefer KiCAD, a free CAD tool which also has PCB layout capabilities. It is possible to run Spice within KiCAD, although I find it a bit more laborious to use.
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Old 16th May 2021, 5:49 pm   #13
kalee20
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Default Re: Using LTSpice for schematics

Can anyone recommend a website or a book to learn LTSpice? I know the basics, but the various Spice Directives, how to use (and write!) macromodels, are all hidden mysteries to me at present.
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Old 16th May 2021, 6:14 pm   #14
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Default Re: Using LTSpice for schematics

Hi Peter, "The LT Spice IV Simulator" Giles Brocard from Wurth Elektronik, possibly one of the books available from Elektor ISBN 978-3-89929-258-9.

It goes in to the full depth but is also quite readable for a beginner and allows you time to progress.
The program is free to download from NI and they also have some good app notes

Ed
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Old 16th May 2021, 7:53 pm   #15
Richardgr
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Default Re: Using LTSpice for schematics

This is a very good place to start with LTSpice, with basic exercises like a tone control ...
Fun With Tubes
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Old 17th May 2021, 7:02 am   #16
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Default Re: Using LTSpice for schematics

Quote:
Originally Posted by Richardgr View Post
This is a very good place to start with LTSpice, with basic exercises like a tone control ...
Fun With Tubes
Excellent link - I wish I'd found that a couple of weeks ago. The 3020 I was using to learn LTSpice & how to simulate tone controls uses inv. log pots for the the tone controls, so while the inv. log. maths were straightforward enough, it took me an embarassing number of hours to find the info needed to assemble the correct spice operatives.... it probably also helps if you don't put (non-linear) pots in upside down

Alan
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Old 18th May 2021, 11:46 am   #17
kalee20
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Default Re: Using LTSpice for schematics

Hi Richard and Ed, thanks very much for the links!
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