arduino/firmware/modbus-sd-VSD-generic/modbus-sd-vsd.md

Modbus Reading for Generic VSD Device

This is a specification and implementation of the Arduino-based Modbus data logger for a Generic VSD Device. This software is designed for Vivarox EMS and only Vivarox has right to use and modify this software.

Arduino Implementation:

This project uses an Arduino to connect to Modbus devices, read information, and log it onto an SD card with timestamps.

Hardware needed:

1. Arduino Board Recommended: Arduino MEGA 2560 (for more memory and I/O pins) or Arduino UNO (for simpler projects).

   • Arduino MEGA @ R377.20
   • UNO R3 with 16U2 USB Interface @ R151.00

2. RS485 to TTL Module Allows communication between the Arduino and Modbus devices using the RS485 protocol.

   • RS485 Module (TTL -> RS485) @ R25.30
   • MAX485 Bus Transceiver (4 Pack) @ R16.00

3. SD Card Module Allows the Arduino to read from and write data to an SD card.

   • Micro SD Card Module @ R25.00

4. RTC Module To keep track of the current date and time, even when the Arduino is powered off.

   • DS3231 Real Time Clock Module @ R55.20

5. Power Supply To power the Arduino and connected peripherals.

   • AC Adapter 9V with barrel jack @ R60

6. LED Indicators Two LEDs for status indication (not included in original cost estimate).

Wiring

RS485 Module to Arduino:

1. RO (Receiver Output) to Arduino RX (pin 8)
2. DI (Driver Input) to Arduino TX (pin 7)
3. DE (Driver Enable) & RE (Receiver Enable) to Arduino digital pin 4
4. VCC to 5V on Arduino
5. GND to GND on Arduino
6. A & B (RS485 differential pair) to Modbus device

SD Card Module to Arduino:

1. VCC to 5V on Arduino
2. GND to GND on Arduino
3. MOSI to MOSI (pin 51 on MEGA, pin 11 on UNO)
4. MISO to MISO (pin 50 on MEGA, pin 12 on UNO)
5. SCK to SCK (pin 52 on MEGA, pin 13 on UNO)
6. CS (Chip Select) to digital pin 10

RTC Module to Arduino:

1. VCC to 5V on the Arduino
2. GND to GND on the Arduino
3. SDA to SDA (pin 20 on MEGA, pin A4 on UNO)
4. SCL to SCL (pin 21 on MEGA, pin A5 on UNO)

LED Indicators:

1. LED A to digital pin 3
2. LED B to digital pin 5

Software

• Modbus Library: ModbusMaster
• SD Library: SdFat (more advanced than the standard SD library)
• RTC Library: RTClib by Adafruit
• NeoSWSerial: For better latency on software serial communication

Implementation Details

1. Modbus Configuration:

   • Slave ID: 101
   • Baud Rate: 9600
   • Register map: Defined in separate "register_map_pm8000.h" file

2. Data Logging:

   • Frequency: Readings taken every second
   • File Format: CSV (Comma-Separated Values)
   • Filename: "pm8k_YYYYMMDD.csv" (generated daily based on current date)
   • Data Structure: Timestamp, followed by register values
   • Header Row: Includes register addresses for easy identification

3. Register Types Supported:

   • Float (32-bit)
   • Integer (32-bit)
   • Long (64-bit)
   • String (up to 20 characters)

4. Error Handling and Status Indication:

   • LED A: Indicates successful data writing and transmission
   • LED B: Indicates errors (e.g., SD card issues, RTC problems, Modbus communication errors)
   • Serial output for debugging (9600 baud)

5. Special Features:

   • Automatic creation of new log file on date change
   • Header row written only once per file
   • Robust error handling for SD card, RTC, and Modbus communication

Programming Workflow

1. Initialize hardware (RTC, SD card, RS485 module)
2. Set up Modbus communication parameters
3. Enter main loop:
   • Read current time from RTC
   • Read data from Modbus registers
   • Write timestamped data to SD card
   • Handle any errors and provide status indication via LEDs
   • Delay for 1 second before next reading

Best Practices

• Start by commenting out registers you don't need before adding new ones.
• If you're using an Arduino UNO, you may need to be more selective about which registers to include due to memory constraints.
• Test your modifications incrementally to ensure the Arduino can handle the memory load.
• If you need to read a large number of registers, consider using an Arduino MEGA or a more powerful microcontroller.

By carefully managing the registers in the register_map_vsd.h file, you can customize this Modbus reader to suit your specific requirements while staying within the memory limitations of your Arduino board.