⚠️ BETA SOFTWARE - See DISCLAIMER for important safety information.

Open-source, modular engine monitoring system for classic cars and vehicles without OBDII diagnostics.

preOBD provides comprehensive engine monitoring for vehicles that lack modern electronic systems. It monitors temperature, pressure, voltage, and RPM sensors, providing data via LCD display, CAN bus (OBDII compatible), serial output, and data logging.

What it does:

• Monitors multiple temperature sensors (thermocouples, thermistors)
• Monitors pressure sensors (oil, boost, fuel)
• Monitors battery voltage
• Monitors engine RPM (via alternator W-phase)
• Monitors vehicle speed (via hall effect sensors)
• Imports sensors from CAN bus (OBD-II, J1939) and combines with local sensors
• Displays data on LCD screen
• Outputs standard OBD-II PIDs via CAN bus (request/response and broadcast modes)
• Logs data to serial and SD card
• Configurable alarms with audible alerts
• Controls 12V relays based on sensor thresholds (cooling fans, pumps, warning lights)

What it doesn't do:

• Engine control (monitoring only, relay outputs are auxiliary only)
• Provide safety certification or guarantees

Platforms:

• Teensy 4.1 (recommended - 8MB flash, built-in SD, native CAN, excellent ADC)
• Teensy 4.0 (2MB flash, native CAN, excellent ADC)
• Arduino Mega 2560 (256KB flash, 8KB RAM, full features)
• Arduino Due, ESP32 (12-bit ADC)
• Arduino Uno (32KB flash, 2KB RAM, limited - see Static Builds)

Sensors:

Temperature:

• K-type thermocouples (MAX6675, MAX31855) for CHT/EGT
• VDO thermistors (120°C, 150°C) for coolant, oil, transmission
• Generic NTC thermistors (10K, with Beta or Steinhart-Hart coefficients)
• Linear temperature sensors (0.5-4.5V output)

Pressure:

• VDO resistive pressure senders (2-bar, 5-bar, 10-bar)
• Generic linear pressure sensors (0.5-4.5V, any range)
• Freescale/NXP MAP sensors (MPX4250)

Other:

• Battery voltage monitoring (with divider)
• W-phase alternator RPM sensing
• Hall effect speed sensors (VDO, OEM, generic 3-wire)
• BME280 environmental (temp, pressure, humidity, altitude)
• Digital inputs (float switches, warning lights)
• Custom calibration support for unlisted sensors

Outputs:

• 20x4 I2C LCD display
• CAN bus with OBD-II request/response (works with ELM327 adapters and Torque app)
• RealDash mobile dashboard (CAN broadcast mode)
• Serial CSV output
• SD card data logging

# Clone the repository
git clone https://github.com/preobd/preOBD.git
cd preOBD

# Build for your platform
pio run -e teensy41      # Teensy 4.1 with built-in SD (recommended)
pio run -e teensy40      # Teensy 4.0
pio run -e mega2560      # Arduino Mega 2560
pio run -e uno_static    # Arduino Uno (static config)

# Upload to your board
pio run -e teensy41 -t upload

# Open serial monitor (115200 baud)
pio device monitor

Configuration Files:

• platformio.ini - Controls which features compile into firmware
• src/config.h - Hardware pins, timing intervals, default units

All builds include all output modules. Use serial commands to enable/disable outputs at runtime.

See Build Configuration Guide for details.

Connect to the serial monitor and enter configuration commands:

CONFIG                                                # Enter CONFIG mode
SET 7 EGT MAX31855
SET A0 OIL_TEMP VDO_150C_STEINHART
SET A1 COOLANT_TEMP VDO_120C_STEINHART
SET A2 OIL_PRESSURE VDO_5BAR_PRESSURE
SET A3 BOOST_PRESSURE MPX4250AP
SET A6 PRIMARY_BATTERY VOLTAGE_DIVIDER
SET I2C:0 AMBIENT_TEMP BME280_TEMP
SAVE
RUN                                                   # Enter RUN mode (starts sensors)

Multi-function button:

• Hold during boot → Enter CONFIG mode
• Press in RUN mode → Silence alarms for 30 seconds
• Hold briefly during RUN mode to toggle display on/off

Serial commands in RUN mode:

LIST INPUTS              # Show configured sensors
INFO A2                  # Show details for one sensor
VERSION                  # Show firmware version

• Quick Reference - Command cheat sheet and common tasks
• Directory Structure - Project file organization

• Sensor Selection Guide - Complete sensor catalog
• Pressure Sensor Guide - Pressure sensor wiring
• Voltage Monitoring Guide - Battery monitoring
• W-Phase RPM Guide - RPM sensing for classics
• Hall Effect Speed Guide - Vehicle speed sensing
• Digital Sensor Guide - Float switches

• Serial Commands Reference - Complete command list
• CONFIG/RUN Mode Guide - Safe configuration workflow
• Alarm System Guide - Alarm state machine
• Relay Control Guide - Automatic relay control for fans, pumps, and lights
• Advanced Calibration - Custom sensor calibrations

• Static Builds Guide - Compile-time configuration for Uno/constrained boards
• Complete Documentation - Full documentation index

SET <pin> <app> <sensor>    # Configure a sensor (e.g., SET A2 COOLANT_TEMP VDO_120C_LOOKUP)
SET <pin> ALARM <min> <max> # Set alarm thresholds
SET <pin> UNITS <unit>      # Set display units (CELSIUS, FAHRENHEIT, PSI, BAR, etc.)
SET <pin> NAME <name>       # Set short display name
CLEAR <pin>                 # Remove a sensor
ENABLE <pin>                # Enable a disabled sensor
DISABLE <pin>               # Disable a sensor
SAVE                        # Save configuration to EEPROM

HELP                      # Show help category overview
HELP <category>           # Show detailed help (LIST, SET, CALIBRATION, etc.)
HELP QUICK                # Show compact command reference
LIST INPUTS               # Show all configured sensors
LIST APPLICATIONS         # Show available application types
LIST SENSORS              # Show available sensor types
INFO <pin>                # Show details for one input
DUMP                      # Show complete system state
VERSION                   # Show firmware version

CONFIG                    # Enter configuration mode
RUN                       # Enter run mode (start monitoring)
RESET                     # Clear all configuration (requires confirmation)
OUTPUT <name> ENABLE      # Enable output module (CAN, Serial, SD_Log, Alarm)
OUTPUT <name> DISABLE     # Disable output module
DISPLAY STATUS            # Show display configuration

preOBD/
├── platformio.ini          # Build configuration
├── README.md               # This file
├── DISCLAIMER.md           # Safety information
├── src/                    # Source code
│   ├── main.cpp            # Main program loop
│   ├── config.h            # Hardware configuration
│   ├── advanced_config.h   # Advanced features
│   ├── inputs/             # Input and sensor management
│   ├── lib/                # Sensor library and calibrations
│   ├── outputs/            # Output modules (CAN, Serial, SD)
│   ├── displays/           # Display modules (LCD, OLED)
│   └── test/               # Test mode system
└── docs/                   # Documentation
    ├── getting-started/    # Quick start guides
    ├── guides/             # User guides
    ├── reference/          # Command reference
    └── advanced/           # Advanced topics

Contributions welcome:

1. Sensor calibrations - Share your sensor data
2. Platform testing - Test on different hardware
3. Documentation - Improve clarity
4. Bug reports - Help make it more reliable

Please:

• Test thoroughly on hardware before submitting
• Document new sensors with datasheets
• Follow existing code style
• Update documentation

Getting Help:

• GitHub Issues - Bug reports and feature requests
• GitHub Discussions - Questions and setup help
• Documentation - Start here for most questions

When asking for help, include:

1. Hardware platform (Arduino Mega, Teensy 4.0, etc.)
2. Sensor types being used
3. Configuration mode (compile-time or runtime)
4. Serial output showing the issue
5. What you've already tried

preOBD is licensed under a custom MIT + NonCommercial License.

• Use the software for personal projects
• Modify, fork, or extend the software
• Publish your modifications (noncommercially)
• Learn from and build upon the source code
• Use it for educational or research purposes

• Sell the software
• Bundle it into a product you sell
• Use it in a for‑profit business
• Monetize it in any form
• Distribute commercial derivatives

For commercial use, contact: info@preobd.com

See LICENSE file for complete terms.

preOBD is beta software. See DISCLAIMER for important safety information and limitations.