AoNArt of Nanoelectronics
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05 · Foundational

Reading and drawing circuit variables

Before writing an equation, show where every circuit-dependent variable lives.

70-95 minFoundational
In this lesson
  • Annotate voltage and current references before calculation.
  • Associate node voltages with a reference node.
  • Place power conventions consistently.
  • Audit a schematic for ambiguous or overlapping labels.
Starting question

What should exist on the page before the first circuit equation is written?

Every circuit-dependent variable in that equation should already have a visible physical reference: a branch, a node pair, a port or an explicitly chosen reference node.

05.1Read the drawing before reading the algebra

Figure 1.1 — Voltage and current referencesThe voltage arrow B→A defines VAB = VA − VB. The current arrow simply defines the positive direction of I.
BAVAB−+I
  1. Identify the branch, port or node pair.
  2. Locate the voltage/current reference arrow.
  3. Associate the symbol with that reference.
  4. Only then interpret the equation using the symbol.

This order makes equations traceable back to physical locations rather than turning symbols into detached letters.

05.2Node voltage requires a reference node

A label VA is shorthand for VA−Vref. A schematic should therefore make the reference node visible before node-voltage equations appear.

When several pages use the same reference, it may be visually economical to state it once—but never to leave the learner guessing which conductor is the zero reference.

05.3One pedagogical question per figure

A schematic is not improved by displaying every known variable at once. If one figure is teaching voltage polarity, another can teach current direction, and a third can show the complete topology.

The rule is simple: show enough information to answer the paragraph's question, and no more.

05.4AoN schematic readability checklist

  • No overlap or near-overlap between symbols, values, node names, arrows or polarity marks.
  • Current and voltage annotations occupy separate visual lanes.
  • Explanatory prose stays in the caption or surrounding text, not inside an electrical symbol.
  • Variables are introduced visually before they appear in a derivation.
  • Dense comparisons are split into separate full-width figures when needed.
  • The figure remains readable at article-column and mobile width.

05.5Audit exercise

Before accepting a schematic, ask:

  1. Can I identify every variable without reading the equation?
  2. Can I tell which terminal is positive for each shown voltage?
  3. Can I tell the positive direction of each shown current?
  4. Is the reference node obvious where node voltages are used?
  5. Would removing any annotation make the figure clearer without losing the lesson?
What is the correct response if a technically correct figure fails one of these questions?
Redesign or split the figure. Pedagogical ambiguity is a publication failure even when the netlist is correct.

05.6Before leaving EF-01

You should now be able to look at a future AoN circuit and identify: the voltage reference, the positive current direction, the power convention, the node reference and the mathematical regime of each symbol.

DC-01 can therefore introduce a resistor and Ohm's law without spending its first pages repairing notation ambiguity.

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