January 14, 2016 at 4:59 pm #1372
Last year, Mike Engelhardt – the creator of Linear Technology’s free LTSpice schematic capture and simulation software – came to Adelaide.
I went along to hear all about it.
It was all good fun, with lots of spruiking about how powerful these circuit modelling tools were, and what a terrific timesaver they were compared to the old methods of hacking up a breadboard to test a new design.
I skulked out of there feeling like a Troglodyte, determined to spend even more time in front of the computer and less time with pen, paper and soldering iron down the back shed.
Look up any number of sources if you want the good oil on why computer models will replace old circuit hackers like me.
What they never mention is that the real advantage of simulating circuits is that you can run them and make measurements in the background while sitting at your computer pretending to answer emails in the foreground.
So I hacked together a few circuits I was thinking about in LTSpice, and then the problems began. All the usual inexplicable and frustrating stream of inscrutable computer messages pinging you in the face and getting between you and the answer: –
“Analysis: Time step too small; time =0.00666736, timestep = 1.26211e-018: trouble with node “ramp””
Suddenly it was all about the tool, and nothing about the circuit.
So I sent off my files to Mike Engelhardt via the local Linear Technology office, and after a couple of months and some prompting from me, the answer came back: –
“… it is difficult to correct other company parts, and there is an issue in the library of the NE555.”
“We have only two engineers including Mike Elgelhart to support LTSpice, so it is sometimes difficult to support all issues on LTSpice especially non-LTC parts libraries”
In my own defence
1) over a billion 555 timer ICs are produced each year, so it’s a pretty common IC and
2) I did find the 555 part in LT’s very own LTSpice library, and
3) all the other parts in my circuit are made by Linear Tech except for this old bipolar 555, and
4) there is no library part for the more modern 7555 CMOS timer which I really wanted to use
By this stage I’d already hacked up the usual breadboard on the bench at home and got it all working using solder, sweat and good old-fashioned test gear.
But the problem remains: solder smoke rising from behind my paperwork is a dead give-away that an old circuit hacker is trying to subvert the system. Spice models – when they can be made to work – are easily hidden when I’m supposed to be at my computer doing management stuff!
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