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The layer of a schematic beyond the base components: semiconductors past the plain diode, the logic gate family in both of its competing graphical conventions, the three different ground symbols, measuring instruments, switching and protective devices, and supply topologies. Two standards govern this area and disagree — IEC 60617 internationally and ANSI Y32.2 in North America — and the recurring lesson is that a diode variant, a transistor type and a whole logic function are each distinguished by one small mark: a bent bar, an arrowhead direction, a circle on a pin.
A resistor crossed by a line marked with a temperature sign.
A resistor in a circle with two arrows pointing at it.
A capacitor with one curved plate and a plus mark.
A capacitor with an arrow drawn across its plates.
A diode whose bar has bent ends like a letter Z.
A diode whose bar ends turn like a letter S.
A diode with two arrows pointing towards it.
A three-terminal transistor with a gate bar separated by a gap.
A field-effect transistor whose gate touches the channel.
A diode with a gate lead, latching once triggered.
Two thyristors drawn back to back with one gate.
A triangle pointing right with two marked inputs.
A triangle with a small circle at its point, inverting the input.
An AND gate with an inverting circle on its output.
An OR gate with an inverting circle on its output.
An OR gate with a second curved line across its back.
A plain triangle passing its input through unchanged.
A rake of three short diagonal strokes under a stem.
A solid downward triangle marking a common reference.
A switch drawn with a marking showing automatic operation.
A breaker marked with a current-comparison box.
A contact operated by a stem with a bar on top.
One contact that can meet either of two others.
A relay coil driving heavy-current contacts.
A coil marked as producing mechanical movement.
A circle containing a capital A, measuring current.
A circle containing a capital V, measuring potential difference.
A filled dot where two wires are connected.
A small semicircular hop where wires cross without joining.
Three lines with a numeral and phase notation.
Three lines meeting at a common point.
A triangle marking three windings joined end to end.
A rectangle opening into a trumpet shape.
A circle on a stem, converting sound into signal.
A stem branching into two upward diagonals.
An LED facing a phototransistor inside one box.
A resistor marked with a voltage-dependence stroke.
A circle with an arrow, delivering a set current.
A circle with a plus and minus or a bar, holding a set voltage.
A line inside a partial enclosure, marking a screened conductor.
A small hollow circle where a wire can be connected.
An arrow on one lead showing the device's polarity.
A dashed rectangle around part of a circuit.
A plain rectangle with a symbol inside naming the function.
A small circle on a lead marking active-low behaviour.
A crystal drawn with two capacitors to ground.
A small marked node intended for measurement.
Letters and numbers stating a fuse's current, speed and voltage.
A plus, a minus, a bar or a chamfer showing which way round.