analogRead printed a flat 1021-1023 on every loop — the collector pinned at
Vcc. Measured in the running app:
base 0.481 V emitter 0.001 V collector 4.994 V
0.481 V is below the ~0.65 V a 2N2222 needs, so the transistor never
conducted and the "amplifier" was an open switch.
The bias divider was fine on paper (47k/10k -> 0.88 V). What broke it was
the 10k "coupling resistor" from the signal generator, whose own comment
claimed it let the generator "wiggle the biased base without DC-shifting
it". It does the opposite: a generator with 0 V offset is ground at DC, so
that resistor sits in parallel with Rb2 —
10k || 10k = 5k -> Vb = 5 * 5/(47+5) = 0.481 V
which is exactly the measured value. Replace it with a 1 uF coupling
capacitor (159 ohm at the generator's 1 kHz: passes the signal, blocks the
DC that was wrecking the bias), and take Rb2 to 15k so the collector sits
near mid-rail — the operating point the sketch's own comment promises and
the only one with room to swing both ways.
The netlist snapshot could never have caught this: the text was exactly
what the author intended. So the new test asserts the PHYSICS — bias in the
active region, collector off both rails, and a collector that actually
swings — resolving node names through the builder's pin map rather than
hardcoding `n2`, and adding the 5 V rail the board supplies in the app.
David Montero Crespo