Ryan Malloy 52e8acf214 Fix 3.3V TX margin: R2 470->220 ohm (parameter sweep validated) ...

At 3.3V VCC the original R2=470 only drives 4.66mA through the
PC817 LED, giving marginal bus pull-down on loaded buses (V_LOW=2.5V
at 1k pull-up). Three parameter sweeps (R2, bus impedance, CTR grade)
identified R2=220 as the fix: LED current doubles to 9.71mA, bus LOW
drops to 0.27V even at 1k pull-up. Validated against PC817A typical
CTR with worst-case bus loading.

2026-02-13 00:56:03 -07:00

reference

Fix 3.3V TX margin: R2 470->220 ohm (parameter sweep validated)

2026-02-13 00:56:03 -07:00

CLAUDE.md

Fix 3.3V TX margin: R2 470->220 ohm (parameter sweep validated)

2026-02-13 00:56:03 -07:00

Description

BMW I/K-Bus + OBD-II K-line interface board (ESP32, optocoupler isolated)

687 KiB

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