Symbulator 9

A plain text input file holds as many entries as you like. An entry is one set of inputs to be solved together: a circuit, the analysis to run on it, and the settings to run it with. Each starts with its name in square brackets, followed by the element lines and then its settings. The file extension is .cir.

A file may also name itself, with a title: line above the first entry — title: Circuits for Lesson 1 of the Tutorial. That title is what the interface shows in place of the filename, and it is what the supplied examples are listed by. A file without one is shown by its filename instead.

# comments start with a hash

title: A couple of problems

[Problem 1 — divider]

e1,1,0,20
r1,1,2,5'k
r2,2,0,15'k

analysis: dc
rounding: exact
si: no
units: yes


[Problem 2 — RC transient]

e1,1,0,10/s
r1,1,2,2200
c1,2,0,4.7e-6

analysis: tr
variables: v_2
rounding: exact
si: no
units: yes

Everything after the element lines is optional, and can be left out entirely — leaving a key out just means the app's own default applies, same as if you'd never touched it: analysis (dc/ac/fd/tr), omega, variables, tool (th/er/port) with n1/n2/kind and with_load (yes/no, the load question), note (text of your own, shown when the entry is loaded — repeat the line for a second paragraph), image (a link to a picture of the circuit, shown above the description when the entry is loaded — a web address, or a path relative to this page; a picture on your own computer cannot be linked to, because the browser will not read your files for a web page, and you may cap how wide it is drawn by writing [400px] after the link), and (if the circuit uses it) the expert-mode equations, conditions and unknowns; the Settings rounding (exact/approx/a number of significant digits/exact+n for both at once), si, units, rms and show_equations (each yes/no); and, if you were using them when you saved, evaluate with its own evaluate_conditions, the standalone equation solver's solve_equations / solve_conditions / solve_unknowns / solve_real_only, and the plot tool's plottool (sweep/bode/bode_tf/plot_time) / plotkey / plotx (the variable on the x-axis) / plotmin / plotmax / plotpoints.

For the two-port tool, a port whose lower terminal is not ground is written as a pair, [top,bottom], in its node field (and in n1/n2 here); a side of the circuit that has no path to node 0 is measured against a reference of its own, and the answers say which.

When the app writes a file it puts the keys in the order shown above — element lines, then the analysis type and Expert Mode, then Settings, then Evaluate, Solve equations and Plot. Nothing that reads a file back in cares about that order, so a hand-written file can put them wherever is convenient.

Two links below the circuit box put the inputs you have on screen into the open file, and only one of them shows at a time: Save inputs to new entry adds them as a new entry, and Update inputs in this entry overwrites the entry you are already working in.

Upload, at the top of this card, reads a file like the one above: its entries become the input file open in your browser, replacing whatever was open before. The file is only read, never stored. Download, beside it, writes the open file back out, and is available whenever that file has at least one entry in it.

One element per line (or separated by :), fields separated by ,; node 0 is ground. See the documentation for a full walkthrough, or pick an example circuit above to see it in practice.

The first letter of an element's name selects its type. Element letters, element names and node names are not case-sensitive: R1 and r1 are the same resistor, and node A is node a.

A value can be a number, a symbol (rload, vin) or an expression — and an expression referring to another answer, like 2*v2, makes a dependent (controlled) source.

TR reads a source value as a function of time: 12 is a 12 V step, u(t) the unit step, t a ramp, δ(t) an impulse. The Greek letter is hard to type, so delta(t) is read exactly the same as δ(t). FD reads it in the s-domain instead: 5/s is a 5 V step and 5 an impulse. To write an FD source in time, wrap it — {5}, {u(t)} — which is shorthand for t2s(…) and works in FD only.

Write the apostrophe — 1'k — to say plainly that you mean an SI prefix. A bare 1k also works, but it is ambiguous (one kilo, or one times a variable named k?) and Symbulator will stop and ask.

Case matters here. 'M is mega and 'm is milli — a factor of a billion apart. (Both 'k and 'K mean kilo.) Micro accepts either u or µ, so a value pasted from a datasheet works as typed. There is no prefix for exa: a bare E glued directly to digits, like 8E3, is read as scientific notation instead — see below for when E/e mean that versus an ordinary variable.

8000, 8000. and 8E3 all mean the same number; the last two are read as approximate rather than exact.

E/e only mean scientific notation when glued directly onto digits with no space or operator in between — 1E3 and 1e3 both mean 1000. Written on their own (E, e), or separated from a number by *, they are ordinary variables like any other: 1*E3 and 1*e3 mean "1 times the variable named E3 / e3", not "1 times E times 3".

When conducting an AC analysis, or an analysis in the AC mode, i, I, j and J all mean the imaginary unit and cannot be used as variable names — write 3j, 3*j or 3*i and you get the same thing, shown as 3j. Outside AC, those four letters are ordinary variable names like any other. pi is π. Every other name you write is an ordinary variable, so Q, S and beta mean what you intend rather than something out of SymPy. Euler's number is exp(1).

In FD analysis s is the complex frequency and in TR t is time; elsewhere both are ordinary variables.

In Evaluate and Solve you can refer to any answer with or without its underscore, in any capitalisation — so i_r1, ir1, i_R1 and IR1 all mean the current through r1. Answers are named v_<node> for node voltages and, per element, i_ current, v_ voltage drop, p_ power, s_ complex power, z_/r_ impedance seen by a source.

One per line, name = expression. Each name is replaced wherever it appears, in the circuit and in every other box. E.g. vx = va-vb, then use vx as a dependent source's value.

Provide additional equations, unknowns and/or conditions to be considered.

The solver opens in a new tab, preloaded with this solve’s equations and results. From there:

• Untick an equation, flip a Known to Unknown, and watch the results follow.
• A transient (TR) solve hands over its answers as functions of time, with t as a Known you can set — or make t the Unknown and find when a waveform reaches a value.
• An FD solve hands over its s-domain system, with s as a Known complex number you can move around the plane.
• Tick Include the derived answers and each element’s power and voltage drop cross too, as equations of their own — arriving unticked, so the sheet still lands on the circuit alone. Tick the one you want; or untick the source’s equation, pin a power Known, and the sheet finds the source value that delivers it.