Examples

Every example in examples/ elaborates and passes the gate. The test suite rebuilds each one and compares what it produces, so none of these is a sketch that no longer runs. Each has a page here carrying its program, the views it renders and the files it writes. Those pages are generated from the folder itself. A page cannot describe a program that has since changed.

Example	Shows
divider/	The smallest real board: two resistors and a capacitor
rc_filter/	One question, answered by ngspice and then at the equation level
antenna_match/	A Touchstone model through an L match, answered in closed form
blinky/	Declared surfaces, connections and a constraint stating intent rather than the answer
equations/	Values chosen by equation and reuse by inheritance
sensor_board/	Interfaces lowering to pins, a recorded decision, a check left undecided
i2c_bus/	A multi-drop bus, addresses as constrained parameters
sensor_node/	Ports that name their controller, cited pin selectors, an address the check reads
buck_regulator/	Requirement, decision, calculations, and a question ngspice answers under load
usb_uart_bridge/	Part selection: manufacturer, MPN, distributor and datasheet
servo_drive/	Composition: one HalfBridge block instantiated three times
jee_advanced/problem_1/	Not a board: four claimed currents, all four decided
jee_advanced/problem_2/	Not a board either: one claimed current, and the two branches that carry none
noninverting_amp/	Not a board: two midband answers, and the reading of the figure they rest on

Running one

fang build   examples/sensor_board/sensor_board.py
fang netlist examples/sensor_board/sensor_board.py
fang view    examples/sensor_board/sensor_board.py ground -o ground.svg

What is in an out/

File	What it is	Command
<name>.net	The KiCad netlist, the artifact a layout tool opens	fang export
<name>.kicad_sch	The KiCad schematic, the sheet Eeschema opens	fang schematic
schematic.svg	KiCad’s own render of that sheet	fang schematic --svg
netlist.txt	The same projection as text: parts, then nets and their pads	fang netlist
checks.txt	Every check that ran, and every one left undecided	fang check
graph.txt	What the elaborated graph contains, by entity kind	fang graph
views/*.svg	The views worth looking at for that board	fang view
rationale.md	The requirements, decisions, calculations and evidence in the graph	none
verification.txt	What each declared question’s tool found, at three significant figures	fang verify

python examples/regenerate.py rewrites them. They are built in the project namespace PRJ-EXAMPLES, which is where the identifiers in them come from. A local fang build defaults to PRJ-LOCAL and derives its own.

What each one is for

divider/ is the smallest thing worth calling a board. Read it to learn the shape of a program and nothing else.

rc_filter/ is the smallest board with a question on it. The corner is a parameter with no value and the constraint over it is undecided, until ngspice measures it in an AC sweep and the number comes back through the gate. Asked again on the committed head, the same question is answered at the equation level and nothing runs.

antenna_match/ carries its antenna as data: a Touchstone file, synthetic and saying so. Its return loss through the L match is read and composed in closed form, with the matching values the graph holds, and the confidence is halved because the model is an assumption.

blinky/ adds the point about constraints. The series resistor is not written as a number that someone computed offstage. The LED current is written as the requirement, and the resistor value has to satisfy it.

equations/ takes that further. Ohm’s law is a constraint rather than a comment, so substituting a part re-checks the arithmetic instead of trusting it. SenseDivider inherits the equations and replaces the two values.

sensor_board/ is the one to read to understand lowering. The MCU offers PB8 and PB6 for the I2C clock. self.mcu.i2c >> self.imu.i2c resolves to one of them and records a decision naming what it rejected. It also leaves a check undecided, because the IMU’s threshold is missing rather than assumed.

i2c_bus/ connects one port several times. Two things a netlist could not keep survive here. The device addresses are parameters, so “no two devices answer to the same address” is a constraint the kernel decides rather than a linter rule. And the RTC’s thresholds are recorded as an assumption, which leaves that link undecided rather than passed.

sensor_node/ puts on the board what the firmware otherwise holds alone. The STM32F401RE’s i2c1 port names I2C1, and each candidate pin carries the alternate function that routes the signal to it, cited from ST’s table. The lowered pin connections carry AF4. The HS3001’s port carries its address, 0x44, and the compatibility check decides the addressing rule from it.

usb_uart_bridge/ shows part selection landing on the instance rather than the class template. The logical part stays “a 3.3 V regulator”. Which one was bought is a separate, cited fact.

buck_regulator/ puts the reasoning in the graph. The requirement, the part decision, the datasheet numbers behind it and two calculations are all entities beside the inductor, so fang can answer “why is this 4.7 µH?” without anyone writing a design document. The requirement is verified by a question rather than asserted: ngspice runs the rail under full load on an ideal power stage whose provenance is an assumption, and measures 3.29 V and 1.90 mV of ripple.

servo_drive/ is composition at size. A HalfBridge owns its interior: its transistors, its shunt and its own constraints. The drive instantiates three of them from one declaration.