Building schematics

mc9.Schematic writes MC9 circuit files from code, with automatic label placement that avoids collisions with MC9's own voltage boxes - so screenshots of Dynamic DC / AC look clean without hand-tuning.

s = mc9.Schematic()
q  = s.add("Q",  "Q1", at=(46, 10), MODEL="BF420")          # kind, name, value, position (grid), rotation, extra attributes
r1 = s.add("R",  "R1", "200", at=(8, 10))
gnd = s.add("GND", None, at=(54, 17))
s.wire(r1.Plus, q.Base)                  # pins by name: part.Plus, part.Base, part.pin("Plus input")
s.node("Ue", (12, 10))                   # name a node (label; usable in curves: v(Ue))
c = s.build("amp", labels="dc")          # auto-place labels, centre + zoom the drawing, write it, return a Circuit

Parts

kind	MC9 part	value attribute	pins
R C L	Resistor, Capacitor, Inductor	RESISTANCE CAPACITANCE INDUCTANCE	Minus, Plus
V	SPICE voltage source (DC 0 AC 1 0 Sin ..., see mc9.sources)	VALUE	Plus, Minus
VB	Battery	VALUE	Plus, Minus
I	Current source	VALUE	Plus, Minus
D	Diode	MODEL	Anode, Cathode
Q QP	NPN / PNP	MODEL	Collector, Base, Emitter
M	NMOS	MODEL	Drain, Gate, Source, Body
OPAMP	op-amp	MODEL	Plus input, Minus input, Output, VCC, VEE
GND	ground	-	PinA

Any other component definition in mc9/templates/base.cir can be used by its MC9 name. Model names (BF420, 1N4148, LM741) are resolved by MC9's own library, so they must exist there.

Geometry

• One grid unit = 8 design px = 16 screen px. Coordinates are integers; pins sit on grid points.
• rot 0/1/2/3 = pointing right / down / left / up; 4-7 are the mirrored versions. Ground symbols hang downward by default.
• A resistor is 6 units long; a transistor is 3 units wide and tall; an op-amp is 9 x 7.
• wire(a, b) accepts points or pins; if they are not aligned it draws an L (via="h" or "v" chooses the corner).

What MC9 requires (and the library enforces)

• Wires join only at endpoints and pins. The library splits T-junctions for you, and also at node-name points.
• Every node needs a DC path to ground (capacitors and current sources do not count).
• A node name attaches only at an endpoint/pin; equally named nodes are one node, and all Ground symbols are node 0.
• Circuits get valid default curves so the first analysis works without configuration.

s.check()          # unwired pins, crossing wires, nodes without DC path to ground
s.audit("dc")      # predicted collisions: labels, node names, MC9's voltage boxes, bodies
s.audit("ac")      # Dynamic AC boxes ('281.418m,172.755') are ~12 grid units wide: keep voltage nodes >= 14 apart
s.pin_nets()       # {(part, pin): net id} exactly as MC9 will join them - compare with your intended netlist

build() calls check() and audit() and warns about every problem it finds. Pass chars= when your voltage values are short or long (default width: 8 characters for dc, 17 for ac).

Where MC9 draws voltages

One box per non-ground node, centred on the first pin of that node (component order); for a named node the box hangs below-right of the name point. Name nodes on free wire points, not on pins, or the name will overlap the part body.

Zoom and position

The drawing is centred in MC9's canvas at 2x zoom; if it is wider than ~100 grid units (labels included) it switches to 1x. Schematic.zoom and crop_px are available after build(), and c.shot(..., "schematic") uses them to crop tightly.