ESP32 OBD-II Toyota HV Current Monitor

Real-time High Voltage (HV) current monitor for Toyota Hybrid vehicles, featuring Bluetooth OBD-II connectivity and LCD display.

📋 Project Overview

This project reads the High Voltage (HV) battery current from Toyota hybrid vehicles using the OBD-II protocol. Data is retrieved via Bluetooth connection to an ELM327 adapter and displayed on a 1602 I2C LCD screen.

Features

• 📊 Real-time HV current reading (200ms update rate)
• 🔋 Battery state display: Charging, Discharging, or Idle
• 📱 Wireless connection via Bluetooth
• 🖥️ Clear LCD 1602 display
• 🔧 Digital filter for stable readings

🛠️ Hardware Requirements

Components

Component	Description	Quantity
ESP32 DevKit V1	Microcontroller with Bluetooth	1
LCD 1602 I2C	16x2 LCD with I2C interface	1
ELM327 Bluetooth	OBD-II adapter with Bluetooth	1
Jumper Wires	Dupont connection wires	As needed
Power Supply	5V USB or car cigarette lighter	1

Pinout

ESP32 ↔️ LCD 1602 I2C

ESP32          LCD I2C
─────────────────────────
GPIO 21   →    SDA
GPIO 22   →    SCL
3.3V      →    VCC
GND       →    GND

Important Notes

• ⚠️ LCD I2C Address: 0x27 (configurable in line 6 of code)
• 📍 If LCD doesn't work, try scanning I2C addresses: i2cdetect
• 🔌 ESP32 connects to computer/power supply via USB
• 📡 ELM327 connects to vehicle via OBD-II port (usually below steering wheel)

ELM327 Specifications

MAC Address: 98:D3:33:F5:C0:E6  (configurable in line 10)
PIN Code:    3080                (configurable in line 180)
Protocol:    ISO 15765-4 (CAN)

Hardware Assembly

LCD display showing startup screen during initialization

🚗 Supported Vehicles

Code is optimized for Toyota/Lexus Hybrid vehicles:

• Toyota Prius (Gen 2, 3, 4)
• Toyota Aqua
• Toyota C-HR Hybrid
• Lexus CT200h
• Lexus ES Hybrid
• Other vehicles with THS (Toyota Hybrid System)

Technical Parameters

• DID (Data Identifier): 221F9A2 (HV current)
• CAN Header: 7D2 (Hybrid system ECU)
• Response: 7DA (ECU response)
• Current Format: 2 bytes signed, Big Endian, units: 0.1A

📦 Installation

1. Environment Setup

# Install PlatformIO
pip install platformio

# Clone the project
git clone https://github.com/amir684/ESP32_OBD.git
cd ESP32_OBD

2. Compile and Upload

# Compile
pio run

# Upload to ESP32 (connect ESP32 via USB)
pio run --target upload

# View Serial output (optional)
pio device monitor

3. Customization

Change ELM327 MAC Address

// Line 10 in main.cpp
uint8_t OBD_ADDR[6] = { 0x98, 0xD3, 0x33, 0xF5, 0xC0, 0xE6 };

How to find the address? Search for the ELM327 via your phone's Bluetooth settings.

Change LCD I2C Address

// Line 6 in main.cpp
LiquidCrystal_I2C lcd(0x27, 16, 2);  // Change 0x27 to your address

Change I2C Pins

// Line 169 in main.cpp
Wire.begin(21, 22);  // SDA, SCL

📊 Code Details

Code Structure

src/
└── main.cpp         # Main code
    ├── ISO-TP       # ISO-TP protocol implementation
    ├── ELM327       # ELM327 initialization
    ├── LCD UI       # Display interface
    └── Loop         # Main loop

Working Principles

1. Bluetooth Connection

SerialBT.begin("ESP32-OBD", true);  // Master mode
SerialBT.setPin("3080");
SerialBT.connect(OBD_ADDR);

2. ISO-TP Protocol

The code implements ISO-TP protocol (ISO 15765-2) for ECU communication:

• Single Frame: Single message (up to 7 bytes)
• First Frame: Start of multi-frame message
• Consecutive Frame: Continuation of message

3. Digital Filter

filtA = 0.85f * filtA + 0.15f * amps;  // Low-pass filter

Simple IIR filter for data smoothing.

4. LCD Display

Line 1: I: +12.3A        (HV Current)
Line 2: DISCHG  OBD:OK   (Status)

States:

• DISCHG - Discharging (electric motor active)
• CHG/REG - Charging/Regeneration (braking)
• IDLE - Idle

🔧 Troubleshooting

ESP32 Won't Connect to ELM327

1. ✅ Check that ELM327 is powered (LED blinking)
2. ✅ Verify MAC address is correct
3. ✅ Try resetting ELM327 (disconnect and reconnect)
4. ✅ Check PIN code matches (3080 or 1234)

LCD Shows Nothing

1. ✅ Check pin connections (SDA/SCL)
2. ✅ Verify I2C address is correct (0x27)
3. ✅ Check backlight is on
4. ✅ Adjust contrast (potentiometer on LCD back)

No Data from Vehicle

1. ✅ Ensure vehicle is on (key in ON position)
2. ✅ Check ELM327 is connected to OBD-II port
3. ✅ Try diagnostic commands via Serial Monitor:

   ATZ      - Reset
   0100     - Test connectivity
   

Data is Jumpy/Unstable

Code already includes filtering, but you can increase it:

filtA = 0.90f * filtA + 0.10f * amps;  // Stronger filter

📈 Future Improvements

• Add SOC (State of Charge) reading
• Data logging to SD Card
• Real-time graphs
• WiFi + Web Server
• Support for Hyundai/Kia vehicles
• DTC error logging

📄 License

This project is licensed under the Apache License 2.0 - see the LICENSE file for details.

🤝 Contributing

Pull Requests are welcome! Please open an Issue first for major changes.

📞 Contact

• GitHub: @amir684
• Email: amir684684@gmail.com

🙏 Acknowledgments

• ELM327 - Elm Electronics
• Arduino-ESP32 - Espressif Systems
• LiquidCrystal_I2C - F. Malpartida

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⚠️ Warning: Use this tool at your own risk. Do not drive while viewing data. Incorrect modifications to the OBD system may damage your vehicle.

Made with ❤️ for Toyota Hybrid Owners