Esp32board

NMEA 2000 Marine Diesel Engine Interface (ESP32-C3)

This project provides an open, high-reliability NMEA 2000 marine engine interface for diesel propulsion engines. Built on the ESP32-C3 microcontroller and ADS1115 16-bit ADCs, it monitors engine speed, operating pressures, temperatures, electrical systems, and alarm conditions, broadcasting them across the vessel's NMEA 2000 CAN network.

High-Level Architecture

                    +------------------------------------+
                    |             ESP32-C3               |
                    |                                    |
Flywheel Sensor --->| GPIO4 (Pulse Interrupt)            |
Stop Relay      --->| GPIO5 (Coil Sense)                 |
Glow Relay      --->| GPIO6 (Coil Sense)                 |
Start Relay     --->| GPIO7 (Coil Sense)                 |
1-Wire DS18B20  --->| GPIO0 (Dallas Temp Bus)            |
                    |                                    |
I2C Bus (SDA/SCL) ->| GPIO8 / GPIO9                      |
                    +-----+------------------------+-----+
                          |                        |
                          v                        v
             +-------------------------+     +------------+
             | 3x ADS1115 16-bit ADCs  |     | CAN / TWAI | (GPIO3 TX, GPIO1 RX)
             | (Running at 5V via LS)  |     +-----+------+
             +------------+------------+           |
                          |                        v
                          |                 +--------------+
  NTC1: Exhaust Water Trap|                 |  NMEA 2000   |
  NTC2: Alternator Temp   |                 |     Bus      |
  NTC3: Engine Room Temp  |                 +--------------+
  NTC4: Gearbox Temp      |
  NTC5: Exhaust Elbow Temp|

Key Hardware Peripherals & Pinout

ADC Mapping (3x ADS1115 @ 5V, 64 SPS)

• ADC1 (0x48, Addr $\to$ GND):
  • AIN0: NTC1 (10K NTC, 5V 4k7 pullup) — Exhaust Water Trap
  • AIN1: NTC2 (10K NTC, 5V 4k7 pullup) — Alternator Temperature
  • AIN2: NTC3 (10K NTC, 5V 4k7 pullup) — Engine Room Air Temperature
  • AIN3: Alternator Voltage Divider (10k / 4.7k)
• ADC2 (0x49, Addr $\to$ VDD):
  • AIN0: Oil Pressure Sender (0–5V sensor)
  • AIN1: Engine Coolant Sensor (12V 1k pullup)
  • AIN2: Engine Block Negative Offset Divider (5V — 10k — ADC — 10k — Engine Block -)
  • AIN3: Engine Starting Battery Voltage Divider (10k / 4.7k)
• ADC3 (0x4B, Addr $\to$ SCL):
  • AIN0: NTC4 (10K NTC, 5V 4k7 pullup) — Gearbox Temperature
  • AIN1: NTC5 (10K NTC, 5V 4k7 pullup) — Exhaust Elbow Temperature
  • AIN2: Fuel Tank Level Sender (European 0–190 $\Omega$, 5V 1k pullup)
  • AIN3: Spare Voltage Divider (10k / 4.7k)

Signal Processing & Calibrations

1. Engine Speed (RPM):
   • Computed from flywheel pulses: $\text{RPM} = \text{Hz} \times 2.0$.
   • Two implementations, selected with RPM_SENSOR_EDGE_TIMING in src/config.h:
     • Edge timing (EdgeRpmSensor, default): the ISR timestamps edges (1 µs) and RPM is computed over whole revolutions, giving a new value every revolution with accuracy limited only by interrupt latency jitter (~0.01–0.04%). Registered as an IRAM interrupt so pulses are not lost during flash writes; edges closer than 150 µs are rejected as glitches.
     • Window counting (RpmSensor): counts pulses over a ~100 ms window; ±1 pulse (±20 RPM) quantisation plus millis() jitter.
   • The ESP32-C3 has no PCNT (pulse counter) peripheral, so hardware counting is not available on this board.
   • The native tests print a side-by-side comparison of both implementations; on the board use the T bench signal.
   • Details, measurements and caveats: docs/rpm_measurement.md.
   • Engine is considered Running when $\text{RPM} \ge 800$ and Stopping when $\text{RPM} < 500$.
2. 10K NTC Thermistors (NTC1–NTC5):
   • Converted analytically using the exact Beta parameter model ($\frac{1}{T} = \frac{1}{T_0} + \frac{1}{\beta} \ln\left(\frac{R}{R_0}\right)$ with $R_0 = 10000,\Omega$, $T_0 = 298.15\text{ K}$, $\beta = 3950\text{ K}$, $R_{\text{top}} = 4700,\Omega$).
   • Provides smooth, continuous sub-0.01°C resolution matching the 16-bit ADS1115 without piecewise discretization or boundary kinks.
3. Engine Block Negative Offset Compensation:
   • Measures voltage drop between boat DC ground and engine block negative caused by heavy alternator charging current: $$V_{block} = 2.0 \cdot V_{adc} - 5.0\text{ V}$$
   • The Volvo Penta coolant sensor is connected to the engine block; its voltage reading and supply rail are automatically adjusted relative to $V_{block}$ to prevent false temperature spikes during high charging.
4. Volvo Penta Coolant Temperature Sender:
   • Evaluated through a dedicated lookup table (coolantTable, 10°C to 120°C) with ratiometric battery supply voltage compensation.
5. Oil Pressure Sensor:
   • Linear 0.5V (0 psi) to 4.5V (100 psi) transfer function with disconnection detection.
6. Fuel Tank Level:
   • Supports European 0–190 $\Omega$ resistive senders (0 $\Omega$ = Empty, 190 $\Omega$ = Full), scaled to 0.0%–100.0%.

Alarms & Raw Water Flow Collapse Protection

• 15-Second Startup Grace Period: Prevents spurious alarms while the engine spins up to idle.
• Raw Water Flow Collapse Protection (Exhaust Elbow NTC5):
  • Evaluates rate-of-rise over a 30-second sliding anchor window. If exhaust elbow temperature climbs $\ge +8.0\text{°C}$ inside 30 seconds once above 35°C baseline, a raw water flow failure alarm is tripped immediately.
  • Absolute over-temperature alarm at $> 45.0\text{°C}$. If sustained for $> 5$ seconds, triggers an Emergency Stop discrete alarm.
• Engine Protection Alarms:
  • Coolant Over-Temperature: $> 97.0\text{°C}$ sustained $> 15$ seconds.
  • Low Oil Pressure: $< 10.0\text{ PSI}$ (68.9 kPa) sustained $> 5$ seconds while running.
  • Low System Voltage: Engine battery $< 11.8\text{ V}$ sustained $> 5$ seconds.
  • Alternator Charge Indicator: Alternator voltage $< 12.2\text{ V}$ sustained $> 5$ seconds.
  • High Alternator Temperature: Warning Level 1 triggered at $> 110.0\text{°C}$.
  • High Engine Room Temperature: Warning Level 1 triggered at $> 70.0\text{°C}$.

Non-Volatile Storage & Event Logging

The flash memory uses a 2MB Application / 2MB SPIFFS partition layout (src/no_ota.csv):

• Engine Hours Accumulator: Accumulated per second while $\text{RPM} \ge 800$, committed to wear-leveled NVS Preferences.
• Persistent Event History: Historical alarms are appended to /events.csv on the SPIFFS filesystem.
• No flash writes while the engine runs: flash writes stall non-IRAM interrupts (CAN today, BLE later) for up to tens of ms during a sector erase. While running, engine hours and alarm events are held in RTC no-init memory (survives crashes, watchdog resets and restarts) and written to flash when the stop relay is energised, when the engine stops and before a CLI restart. A valid RTC copy that is ahead of flash is recovered at boot. A backstop save of engine hours every ENGINE_HOURS_BACKSTOP_SAVE_S (default 3600 s, 0 disables) protects against an abnormal power cut; board power normally stays on 30–60 s after shutdown. Alarm flags are still sent immediately in PGN 127489. Setting hours (E) and clearing events (C / N2K command) write immediately.
• GPS UTC Synchronization: Automatically synchronizes timestamps when NMEA 2000 System Time (PGN 126992) is received from on-bus GPS receivers.

NMEA 2000 Messages & Display Remapping

To allow standard marine multifunction displays (MFDs) and dedicated instruments (such as Raymarine i70) to present all engine and electrical metrics without proprietary software:

Interactive Serial Console

Connect to the USB Serial port at 115200 baud for real-time monitoring and commands:

• h — Show command menu
• s — Print complete formatted engine status dashboard
• F — Toggle Fake 1000 RPM mode for bench testing
• E — Set / calibrate accumulated engine hours
• l — Dump SPIFFS alarm event log
• C — Clear SPIFFS event history
• d — Toggle raw ADC voltage debug stream
• T — Cycle the RPM bench test signal on GPIO2 (off → 100 Hz → 400 Hz → 1500 Hz) and print min/mean/max/std-dev of the measured RPM every 2 s. Wire GPIO2 → 1K → GPIO4 and short the flywheel input (J15) so the LM393 output is released. Build once with each RPM_SENSOR_EDGE_TIMING setting to compare.
• R — Software restart of the ESP32-C3

Building & Flashing

This project uses PlatformIO:

# Build firmware
pio run

# Flash to ESP32-C3
pio run -t upload

# Open Serial Monitor
pio device monitor