Simulates the full RS-485 half-duplex channel on the ESP32+CAN+RS485 board:
- SN65HVD1781 behavioral driver/receiver (3.3V native, 32 unit loads)
- Half-duplex direction control via DE/RE GPIO4
- 560Ω bias resistors keeping bus HIGH during idle (NMEA 0183 failsafe)
- 120Ω termination at both ends of a 10m T-line model (Zo=120, Td=50ns)
- Transmits ASCII 'G' (0x47) at 4800 bps — one complete NMEA character
- Second node as passive 12kΩ unit-load receiver
- .meas directives verify Vdiff > ±200mV (RS-485 spec) in both polarities
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
Four .cir behavioral simulations ready to open in LTspice via File→Open:
1_buck_chain.cir — dual MP2338 12V→5V→3.3V, verifies Rfb math + soft-start
2_output_stage.cir — PC817 + IRLML6344 isolated output (inverted logic confirmed)
3_analog_input.cir — analog input conditioning; flags ADC overvoltage on IN-BAT/WATER/OILP
4_nmea2000_can.cir — MCP2562T CAN transceiver, two-node NMEA2000 bus, T-line model
CRITICAL finding in 3_analog_input.cir: R_high=10K + R_low=15K gives 4.3V
at ESP32 ADC when measuring a 12V battery — exceeds 3.3V limit. Fix: use
R_high=100K (same as IN-RPM, which is correctly designed at 3.06V @ 14.4V).
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
alro65