Monitor Your Energy Bill Via Modbus, Mkr Wifi 1010 And Rs485

Setup

Software

Start your computer and open your IDE. You can use the Arduino IDE or Arduino Create Editor. The code is meeting the following requests:

• Modbus communication,
• WiFi management
• MQTT protocol

Modbus is and open source protocol for industrial sensors and machines. To make Arduino talk Modbus, we are going to use the Arduino Modbus library. This library packs all the handlers and makes hooking up any Modbus device really fast. Since we are going to read registers, following the datasheet of the meter, we can find all the information we need like function codes, address of the register and size of the register in words. But to make it clearer, let us explain how Modbus works:

Modbus messages follow a simple structure:

01 03 04 00 16 00 02 25 C7

0x01 is the Device Address

0x03 is the Function Code that tells the device if we want to read or write data *in this case read holding registers

0x04 for Byte Count00 16 - We send 4 bytes of register address (00 16) that tells the device what we want to read

00 02 - then the size of the register (00 02) in words (every word is 2 bytes long)

Last 4 bytes are CRC code. This code is generated from a math function over previous bytes, this ensures the message has been received correctly.

In Arduino all this stuff is handled in the if condition:

// Created by Alberto Perro - Officine Innesto
//
// Read integer from a modbus device holding registers
float readCurrent(){        
    float ampere = 0.;    
    //next command format the request and send it over RS485        
    if (!ModbusRTUClient.requestFrom(0x01, HOLDING_REGISTERS, 0x0016, 2))
    {         
    //Error Handling          
    
    Serial.print("failed to read voltage! ");    
    Serial.println(ModbusRTUClient.lastError());         
    
    } else {        
        uint16_t word1 = ModbusRTUClient.read(); //reading MSW from buffer
        uint16_t word2 = ModbusRTUClient.read(); //reading LSW from buffer
        int32_t milliamp = word1 << 16 | word2;   //join words to retreive int
        ampere = milliamp/1000.0;                 //convert to ampere    
    }        
return ampere;}

In the else part we have the response handler.

Since this register is two words long, we have to join them with binary math. We read the words from the buffer and store them in an unsigned integer 16-bit long (2 bytes or a word), then we join them in a signed integer 32-bit long bitshifting the first word to the left and apply an OR over the second word. This way we retreive the current measurement in mA, dividing it by 1000 we have current in ampere.

This same process is adapted to everything we want to read.

The rest of the code is dedicated to handling MQTT and WiFi networking.

Home Assistant Integration

Adding the meter to Home Assistant is pretty straightforward. Assuming you have a MQTT broker configured (Here is the guide), all you need to do is to add new definitions under the configuration.yaml file. 

sensor:  
    - platform: mqtt    
      name: "Main Voltage"    
      state_topic: "energy/main/voltage"    
      unit_of_measurement: "V"

Here you have to put the name of the measurement, the MQTT topic to read and the measurement unit of the quantity. Save the file, check the configuration and reload Home Assistant, now the measurements will appear on the main page.

Home Assistant consumption panel showing current readings

Home Assistant will take care of creating graphs and automate processes triggered by your readings. This tutorial has finished, now it's up to you to add features and customize it for your own purposes!

CODE

Modbus RTU to MQTT bridge for Finder

This sketch provides a full bridge between the finder energy meter and mqtt. Developed to monitor electricity costs and usage in Casa Jasmina.

Modbus_RTU_to_MQTT_bridge_for_Finder by officine-innesto