Parts

from fang.parts import Capacitor, Resistor
from fang.lang import V, kOhm, uF

top = Resistor(resistance=10 * kOhm, package="R_0603_1608Metric")
cap = Capacitor(capacitance=100 * uF, voltage_rating=16 * V)

A generic part has no manufacturer

Everything in the library is a GenericPart: a part with no vendor identity. That is a deliberate absence, not an unfinished state. A design that says “a 10 kΩ resistor” is complete at the stage it is at; attaching a manufacturer before one has been chosen would be inventing a fact.

select() attaches the vendor identity later, to the instance, without replacing the logical part.

The library

Part	Parameters	Surfaces
Resistor	resistance, power_rating, tolerance_pct	p1, p2
Capacitor	capacitance, voltage_rating, tolerance_pct	p1, p2
Inductor	inductance, current_rating, dc_resistance	p1, p2
Diode	forward_voltage, forward_current, reverse_voltage	p1, p2
LED	the Diode set, plus luminous_intensity	p1, p2
Fuse	current_rating, voltage_rating	p1, p2
Crystal	frequency, load_capacitance, tolerance_ppm	p1, p2
Transistor	vds_max, id_max, rds_on, vgs_threshold	gate, drain, source
Regulator	output_voltage, input_voltage_max, output_current_max, dropout_voltage, quiescent_current	vin, vout (power ports)
Connector	current_rating, voltage_rating	shell, plus per-instance pins
TestPoint	none	probe
MountingHole	diameter	mount

DecouplingCapacitor is a Capacitor whose job is stated, so a checker can find it. It is not in LIBRARY because it is a role, not a distinct part.

Every parameter is optional

Resistor(resistance=10 * kOhm)     # power_rating unstated

An unstated parameter is unknown, and any check that needed it reports undecided rather than assuming a value. If a resistor’s power rating matters to a constraint, the constraint says undecided until someone supplies it.

Packages and footprints

Resistor(resistance=10 * kOhm, package="R_0603_1608Metric")

package= attaches a Footprint trait. Where a part lands physically is a trait rather than a parameter, because it is a fact about the realization, not about the electrical behaviour.

Traits

Behaviour attaches to a part without widening its class:

Trait	Carries
Footprint	Where a component lands physically
Sourcing	Manufacturer, MPN, distributor codes
DatasheetEvidence	The document a component’s claims are cited from
Simulatable	A model, as data. The backend is not here
Renderable	A view-compiler hint carrying no geometry and no meaning

Writing your own

Subclass Part and declare parameters, surfaces, pins and a pin map:

from fang.interfaces import I2CPort, Pin, PinMap
from fang.lang import Parameter, Part, V

class IMU(Part):
    i2c = I2CPort(voltage=3.3 * V)
    supply_current = Parameter("A", description="run current")
    SCL = Pin("SCL", role="clock", number="4")
    SDA = Pin("SDA", role="data", number="5")
    pinmap = PinMap({"i2c.scl": "SCL", "i2c.sda": "SDA"})

Nothing registers it. A part is a class, and using it is how it enters a design.