LT Spice challenge

So, left-to-right is the node number? Not a time axis? And, node voltage is the vertical axis?

Are you looking for a slide show, one node per slide?

It's the node number, but if LT spice wants to plot it as time, I don't mind. 0-20 seconds could be equivalent to node numbers.

Vertical would be node voltages.

No, all 20 node voltages plotted on the screen, left to right.

Imagine a 20-tap voltage divider with equal resistors, makes a straight line. Unequal Rs could trace out a curve.

You want a bar graph of 20 different voltages.

Don't know how to do that, but it can make 20 graphs in different colors. Of course, I don't think LT spice can even use 20 colors, so not all different.

Isn't there a way to write a simple equation based on time that will put that into a single signal? I could do that pretty easily in Excel, but LTspice is pretty grody. Try the LTspice group. They still have some knowledgeable folks there, but you have to be nice to them.

Sounds like a table, rather than a plot.

You can always swap an axis to get a vertical plot.

RL

I want a plot.

LT Spice now has the ADG1208 analog mux. Three of them lets me scan 24 points. I can drive them from a 1 Hz counter or a few pulse generators.

Shift register from D flops plus analog switches.

Sure, but that's a chore and isn't very interactive. People (and mice) learn from rapid feedback.

Yes, but a few analog mux's and a counter is less busy. I just noticed that LT Spice now includes the ADI analog mux chips.

Six pulse generator voltage sources would generate the addresses and enables for three 8:1 mux chips. I guess one could use the LT counter element as a ripple counter too... 4 of those.

Switches with a .model can be made (almost) perfect. One less thing to worry about.

OK, but keep it in mind when you need to do some curve fitting, especially to noisy data.

I like to stay inside Spice when I can. As in adding a lowpass filter for looking at wideband data. My current case would have no noise. Spice doesn't do time-domain noise.

Mike E says that the true value of Spice is for training your instincts. That works best with rapid visual shape-based feedback.

And each switch operated with its own delayed pulse voltage source...

PULSE(0 5 {1*Td} 1u 1u 1m) PULSE(0 5 {2*Td} 1u 1u 1m) PULSE(0 5 {3*Td} 1u 1u 1m) etc

Sure it does. You can use Box-Mueller. You can also add shot noise, as in optical transimpedance amplifiers.

I'd post the ASC files, but they will suffer from word wrap in the text portions and never load. I'd zip them up and post to google drive, but that is turning out to be a real pain. I just got my own website at

but I was having problems linking to their nameservers in Filezilla. They sent me an email giving all the directions, but I haven't had time to implement them yet. Soon...

I agree. I am still amazed that one man can write such a powerful program. Have you ever been to one of his seminars? Absolutely amazing! I still have the T-shirt, but I washed it in a load of laundry using bleach, and it turned pink so I can't wear it. But I keep it as a memento.

Hello John, So the issue is LTSpice won't plot that many (n=20) in one graph? Sorry, I use MicroCap, not LTSPice. Plotting 20 nodes is no sweat in MicroCap.

Or, you want 20 separate plots, each in its own window? That, I can't do either.

In any case, I would export* the data & graph it in Excel.

*In MicroCap: Run Transient Analysis (Alt-1). F10 > Numeric Output > Check All, Data Points=Actual, "OK" Re-run Transient Analysis (F2), see Numeric Output (F5)

cheers, RS

No. I want a screen where X-axis is node number and Y axis is the voltage on each node, left to right. That graphs a voltage trend line along a row of nodes.

Looks like a time-stepped analog mux is the best (only?) way to do that.

One approach is to use another program (probably using the BM algorithm under the covers) to generate .wav files and using those. They can be summed together with different delays to generate new instances of the random noise.

You can also add shot noise, as in

Only in .noise simulations, and it's non-obvious. I got it working once but then just bailed out because the math is so simple anyway.

Cheers

Phil Hobbs

Sure, you can make time-domain noise sources and add them into a circuit, but that is a real nuisance when you need a lot of them.

I've used the Spice random functions.

One of my guys attended and learned a lot of tricks.

I went to one 15 or so years back. Not a bad use of a day.

Cheers

Phil Hobbs