Monitor Your Energy Bill with Modbus and the Arduino IoT Cloud

Introduction

If you really want to make your home smarter, you'll probably want start from your monthly bills (for example, energy, gas, etc...). As some say: good for the planet, the wallet and the bottom line. In this tutorial, we are going to learn how to connect a Modbus energy meter to the Arduino Cloud IoT using an Arduino® MKR WiFi 1010 board and an Arduino® MKR 485 Shield.

Goals

The goals with this tutorial are:

• Learn how to connect a Modbus energy meter to the Arduino Cloud IoT.
• Learn how to use the Arduino® MKR 485 Shield with an Arduino® MKR WiFi 1010 board.

Hardware and Software Needed

The hardware and software used in this tutorial:

• Arduino Cloud IoT.
• Arduino Create Agent.
• Arduino Modbus library
• Arduino® MKR WiFi 1010 board.
• Arduino® MKR 485 Shield.
• Finder Type 7E.64 Energy Meter.
• Twisted single pair shielded cable.
• Micro USB cable.

Electric Meters a.k.a Energy Meters

Energy consumption awareness is a key factor to reduce energy costs and improve energy efficiency; we can measure energy consuption using electric meters, a.k.a energy meters.

Electric meters, also known as energy meters, are electronic devices that can measure the amount of energy consumed by an electrically powered equipment such as a refrigerator or a lamp. Energy meters can be use also to measure the energy consuption of houses and buildings. While different types of energy meters exist, in this tutorial we choose a Finder Type 7E.64 Energy Meter. This energy meter is designed for DIN rail use and fits perfectly in the main cabinet of our house. Also, this energy meter has a RS-485 Modbus interface, this is an industrial communication protocol that can be decoded in Arduino boards using an Arduino MKR 485 Shield and the Arduino Modbus library.

Setting Up the Finder Type 7E.64 Energy Meter

First, you must install the energy meter in your electrical cabinet. To ensure you are working in a safe environment, turn off the power from the electrical terminal ahead of your system and double check with a multimeter that there is no voltage between the terminals.

Warning! Check your country regulations about dealing with your house electrical system and be extremely careful because it can be deadly! If you don't know how, call an electrician.

Place the energy meter inside your cabinet and connect the live and neutral wires from the main breaker to the input of the meter, remember to use the standard color convention (blue for neutral and brown/black/grey for live in EU. The output has to be connected to the rest of the system.

Now it is time make the connection between the energy meter and our MKR WiFi 1010 board! For this, we will use twisted single pair cable with ground. This type of cable is typically used for phone lines, so it can be used to transmit electrical signals over long distances (up to 1.2 km). However, we are going to use a cable long enough to exit the cabinet and place our MKR WiFi 1010 board in an accessible place.

The RS-485 standard names its terminals A, B and COM. A common de-facto standard is the use of TX+/RX+ (or D+) as an alternative for B (high for mark i.e. idle) and TX-/RX- (or D-) as an alternative for A (low for mark i.e. idle). As shown in the image above, we connected the red cable to the D+ terminal, the white cable to the D- terminal and the brown cable to the COM terminal of the energy meter. You can read more about the RS-485 standard here.

The Finder energy meter supports half-duplex communication, this means that data can move in two directions, but not at the same time. The MKR 485 Shield supports both half and full-duplex communication (this means data moving in two directions simultaneously), so we need to set up the shield for half-duplex communication. In the MKR 485 Shield, half-duplex communication uses Y and Z terminals, Y terminal is B or D+ and Z terminal y A or D-, this means that the red cable must be connected to Y terminal and the white cable to Z terminal; the brown cable (COM) must be connected to ISOGND terminal. Also, we need to set the second switch to HALF (2 to OFF) and the third switch to Y-Z (3 to ON): the first switch is not used in half-duplex communication. The third switch is used for setting up the termination, this is a resistor connecting the two data terminals that is used for dampening interferences. The complete shield setup is shown in the image below:

Now, we can connect the MKR 485 Shield and the MKR WiFi 1010 board:

Now that we have finished setting up the hardware, it is time to connect our energy meter to the Arduino Cloud IoT

Setting Up the Arduino Cloud IoT

First, we need to register and configure our MKR WiFi 1010 board in the Arduino Cloud IoT. Let's start by navigating to Arduino Cloud IoT.

Note: You will need a Arduino account to use the Arduino Cloud IoT. If you do not have one, you will be redirected to the account registration site.

Configure a New Device in the Arduino Cloud IoT

Once we are in the Arduino Cloud IoT, we will need to select "Devices" tab. This will open a new page which will ask you to add a new device. Click on the "ADD DEVICE" button.

In the set up wizard, we will now have an option of either configuring a new Arduino® device, or a third party device. Let's select the "Set up an Arduino device" option.

At this point, we will need to connect our MKR WiFi 1010 board to our computer; we will also need to have installed the Arduino Create Agent in our computer. If the Arduino Create Agent is not installed, the set up wizard will ask us to install it. Our device should now show up as shown in the image below. Now its time to configure it, let's select the "CONFIGURE" button.

Now we must name our device. In this case, we named our device as "EnergyMeter001"; names can be randomly generated also by the set up wizard. Let's continue by selecting the "NEXT" button.

After selecting the "NEXT" button, the set up wizard will start to configure our board. This process may take a few minutes.

Once it is done, select the "DONE" button, we will be redirected to the "Devices" page. In this page we are going to be able to see our device. Congratulations! The configuration of our board and the Arduino Cloud IoT is done, now we can create a "Thing" with it.

Create a New Thing in the Arduino Cloud IoT

After our board is configured in the Arduino Cloud IoT, we can move on to the next step: creating a "Thing". Let's select the "Things" tab and then select the "CREATE THING" button.

We will be redirected to a page with our "Thing" configuration overview. Here we can define our "Thing" name, select to what network we are connecting to, what device we are using with out "Thing" and create variables that we want to to connect from our board to our "Thing" in the Arduino Cloud IoT.

Let's start by giving a name to our "Thing" and linking our freshly configured device. We named our Thing as "Energy Thing", this can be done by clicking in "Untitled". To link out freshly configured device, we select the "Select Device" button located to the right. This will open up a window where we can associate a previously configured device with our "Thing" by selecting the "ASSOCIATE" button.

Creating Variables for a "Thing" in the Arduino Cloud IoT

Now, let's create variables for the "Energy Thing". The variables we are going to create will be synced, automatically, with the Arduino Cloud IoT as long as the board is connected to Internet and the Arduino Cloud IoT. Let's create create a new variable by selecting the "Add Variable" button.

This will open up a window where we can create new variables and define its characteristics. The first variable we are going to create will be named "voltage"; this variable will have the following characteristics:

• Variable type: Floating Point Number.
• Variable permission: read only.
• Variable update policy: on change (threshold do not changes).

Repeat this process for the variables and its characteristics shown in the table below:

The created variables should appear now in the "Energy Thing" overview.

Network Credentials for a "Thing" in the Arduino Cloud IoT

Now that we have created the variables for the "Energy Thing", we can configure the network details. This can be done by selecting the "Configure" button in the "Network" section. This will open up a window where we can add the network SSID and its password.

Creating an Sketch for a "Thing" in the Arduino Cloud IoT

Once we are finished with all the configurations of the "Energy Thing", we can move on to creating the sketch that we are going to upload to our MKR WiFi 1010 board. To do so, we first need to go to the "Sketch" tab. But before, let's talk about Modbus.

Modbus is an open source communication protocol designed specifically for industrial sensors and machines. In simple terms, it is a method used for transmitting information over serial lines between electronic devices. Our MKR WiFi 1010 board can talk Modbus using the Arduino Modbus library. This library packs all the handlers and makes hooking up any Modbus device to some of the Arduino® boards (like the MKR family boards) really fast and easy. You can read more about Modbus here.

In the datasheet of the energy meter we can find all the Modbus related information we need like its function codes, address of its registers and also their sizes.

Modbus messages follow a simple structure, for example:

01 03 04 00 16 00 02 25 C7

In this structure:

• 0x01

  is the device address.

• 0x03

  is the function code that tells the Modbus device if we want to read or write data. In this tutorial, we want to read data from the holding registers of the energy meter.

• 0x04

  for byte count, this specifies how may data items are being returned.

• 00 16

  is register address from the Modbus device we want to read.

• 00 02

  is the size of the register in words (every word is 2 bytes long).

• 25 C7

  is a CRC code. This code is generated from a math function over previous bytes, it ensures that the message has been received correctly.

The Arduino Modbus library handles this structure. For example, for reading the register of the energy meter that holds information about current, we have the following function that uses the

requestFrom()

Copy
1/* 
2Function readCurrent()
3Description: read current value from the Finder energy meter holding registers
4
5Created by Alberto Perro (Officine Innesto)
6Modified by José Bagur
7*/
8
9float readCurrent() {        
10  float ampere = 0.;
11  // Send reading request over RS485      
12    if (!ModbusRTUClient.requestFrom(0x01, HOLDING_REGISTERS, 0x0016, 2)) {
13      // Error handling   
14      Serial.print("- Failed to read the current! ");    
15      Serial.println(ModbusRTUClient.lastError());         
16    } else {        
17      // Response handler 
18      uint16_t word1 = ModbusRTUClient.read();  // Read word1 from buffer
19      uint16_t word2 = ModbusRTUClient.read();  // Read word2 from buffer
20      int32_t milliamp = word1 << 16 | word2;   // Join word1 and word2 to retrieve current value in milliampere
21      ampere = milliamp/1000.0;                 // Convert current to ampere
22    }        
23return ampere;
24}

In the

else

The complete sketch we are going to upload to out MKR WiFi 1010 board can be found below, notice that the Arduino Cloud IoT generated automatically the code that is dedicated to handling Internet connectivity:

Copy
1/* -----------------------------------------
2 * Finder Energy Meter to Arduino Cloud IoT
3 * -----------------------------------------
4 * This sketch provides a full bridge between the Finder energy meter and the 
5 * Arduino Cloud IoT. This sketch was developed to monitor electricity costs 
6 * and usage in Casa Jasmina.
7 *
8 * Created by Alberto Perro (Officine Innesto)
9 * Modified by José Bagur
10*/
11 
12#include <ArduinoRS485.h>
13#include <ArduinoModbus.h>
14
15#undef ON
16#undef OFF
17
18#include "thingProperties.h"
19
20unsigned long rate = 60000; // Default refresh rate in ms
21unsigned long lastMillis = 0;
22
23void setup() {
24  // Initialize serial port at 9600 bauds and wait for it to open
25  Serial.begin(9600);
26  delay(1500); 
27
28  // Defined in thingProperties.h
29  initProperties();
30
31  // Connect to Arduino Cloud IoT
32  ArduinoCloud.begin(ArduinoIoTPreferredConnection);
33  
34  /*
35     The following function allows you to obtain more information
36     related to the state of network and Cloud IoT connection and errors
37     The higher number the more granular information you’ll get
38     The default value is 0 (only errors)
39     Maximum is 4
40 */
41  setDebugMessageLevel(2);
42  ArduinoCloud.printDebugInfo();
43  
44  // Start Modbus RTU client
45  if (!ModbusRTUClient.begin(9600)) {
46    Serial.println("- Failed to start Modbus RTU Client!");
47    while (1);
48  }
49}
50
51void loop() {
52  // Update "Energy Thing" variables connected to Arduino Cloud IoT
53  ArduinoCloud.update();
54  
55  // Update energy meter data and show it via the Serial Monitor
56  if (millis() - lastMillis > rate) {
57    lastMillis = millis();
58  
59    voltage = readVoltage();
60    delay(100);
61    current = readCurrent();
62    delay(100);
63    power = readPower();
64    delay(100);
65    frequency = readFreq();
66    delay(100);
67    energy = readEnergy();
68  
69    Serial.print("- " + String(voltage, 3) + "V " + String(current, 3) + "A " + String(power, 3) + "W ");
70    Serial.println(String(frequency, 3) + "Hz " + String(power, 3) + "kWh");
71    delay(100);
72  }   
73}
74
75/* Functions to read Finder energy meter holding registers
76 * For more information: https://gfinder.findernet.com/public/attachments/7E/EN/PRT_Modbus_7E_64_68_78_86EN.pdf
77 */
78
79/* 
80Function readVoltage()
81Description: read voltage value from the Finder energy meter holding registers
82*/ 
83float readVoltage() {
84  float volt = 0.;
85  // Send reading request over RS485 
86  if (!ModbusRTUClient.requestFrom(0x01, HOLDING_REGISTERS, 0x000C, 2)) {
87    // Error handling
88    Serial.print("- Failed to read the voltage! ");
89    Serial.println(ModbusRTUClient.lastError()); 
90  } else {
91    // Response handler 
92    uint16_t word1 = ModbusRTUClient.read();  // Read word1 from buffer
93    uint16_t word2 = ModbusRTUClient.read();  // Read word2 from buffer
94    uint32_t millivolt = word1 << 16 | word2; // Join word1 and word2 to retrieve voltage value in millivolts
95    volt = millivolt/1000.0;                  // Convert to volts
96  }
97
98  return volt;
99}
100
101/* 
102Function readCurrent()
103Description: read current value from the Finder energy meter holding registers
104*/
105float readCurrent() {        
106  float ampere = 0.;
107  // Send reading request over RS485      
108  if (!ModbusRTUClient.requestFrom(0x01, HOLDING_REGISTERS, 0x0016, 2)) {
109    // Error handling   
110    Serial.print("- Failed to read the current! ");    
111    Serial.println(ModbusRTUClient.lastError());         
112  } else {        
113    // Response handler 
114    uint16_t word1 = ModbusRTUClient.read();  // Read word1 from buffer
115    uint16_t word2 = ModbusRTUClient.read();  // Read word2 from buffer
116    int32_t milliamp = word1 << 16 | word2;   // Join word1 and word2 to retrieve current value in milliampere
117    ampere = milliamp/1000.0;                 // Convert current to ampere
118  }
119
120  return ampere;
121}
122
123/* 
124Function readPower()
125Description: read power value from the Finder energy meter holding registers
126*/
127double readPower() {
128  double watt = 0.;
129  // Send reading request over RS485
130  if (!ModbusRTUClient.requestFrom(0x01, HOLDING_REGISTERS, 0x0025, 3)) {
131    // Error handling   
132    Serial.print("- Failed to read power! ");
133    Serial.println(ModbusRTUClient.lastError());
134  } else {
135    // Response handler 
136    uint16_t word1 = ModbusRTUClient.read();  // Read word1 from buffer
137    uint16_t word2 = ModbusRTUClient.read();  // Read word2 from buffer
138    uint16_t word3 = ModbusRTUClient.read();  // Read word3 from buffer
139
140    uint64_t milliwatt;
141
142    // Join word1 and word2 to retrieve power value in milliwatt
143    if (word1 >> 7 == 0) {
144      milliwatt = word1 << 32 | word2 << 16 | word3;
145    } else {
146      word1 &= 0b01111111;
147      milliwatt = 0b1 << 48 | word1 << 32 | word2 << 16 | word3;
148    }
149
150    watt = milliwatt/1000.;                   // Convert power to watts
151  }
152
153  return watt;
154}
155
156/* 
157Function readFreq()
158Description: read frequency value from the Finder energy meter holding registers
159*/
160float readFreq() {
161  float freq = 0.;
162  // Send reading request over RS485
163  if (!ModbusRTUClient.requestFrom(0x01, HOLDING_REGISTERS, 0x0040, 2)) {
164    // Error handling   
165    Serial.print("- Failed to read frequency! ");
166    Serial.println(ModbusRTUClient.lastError());
167  } else {
168    // Response handler 
169    uint16_t word1 = ModbusRTUClient.read();  // Read word1 from buffer
170    freq = word1/1000.0;                      // Retrieve frequency value
171  }
172  return freq;
173}
174
175/* 
176Function readEnergy()
177Description: read energy value from the Finder energy meter holding registers
178*/
179double readEnergy() {
180  double kwh = 0.;
181  // Send reading request over RS485
182  if (!ModbusRTUClient.requestFrom(0x01, HOLDING_REGISTERS, 0x0109, 3)) {
183    // Error handling   
184    Serial.print("- Failed to read energy! ");
185    Serial.println(ModbusRTUClient.lastError());
186  } else {
187    // Response handler 
188    uint16_t word1 = ModbusRTUClient.read();            // Read word1 from buffer
189    uint16_t word2 = ModbusRTUClient.read();            // Read word2 from buffer
190    uint16_t word3 = ModbusRTUClient.read();            // Read word3 from buffer
191    uint64_t dwh = word1 << 32 | word2 << 16 | word3;   // Join word1 and word2 to retrieve energy value in dwh
192    kwh = dwh/10000.0;                                  // Convert energy to kwh
193  }
194  return kwh;
195}

Creating a Dashboard in the Arduino Cloud IoT

After our code has been successfully uploaded to our board, we we will need to create a dashboard for visualizing the energy meter data. Head over to the "Dashboards" tab and click on "Build Dashboard".

An empty dashboard will be displayed. After changing the new dashboard's name, for example "Energy Meter Dashboard", let's add widgets to it. Let's click on the "ADD" button and select a "Value" widget.

Now, we need to link the widget we just added to our dashboard to one of the energy meter variables we defined previously in the "Energy Thing" (voltage, current, power, frequency and energy). This can be done by selecting the "Link Variable" button and then selecting the variable you want to link with the widget; let's start with the variable voltage; remember also to give a name to the widget.

Follow the steps described above to link the rest of the variables of the "Energy Thing" to value widgets. We should see now all of the energy meter data being displayed on the dashboard, the data shown should update every

60000

That's it! You have now a Modbus energy meter connected to the Arduino Cloud IoT!

Troubleshoot

Sometimes errors occur, if the code is not working or data is not in the to the Arduino Cloud IoT there are some common issues we can troubleshoot:

• Missing a bracket or a semicolon.
• Accidental interruption of cable connection.
• Wrong network credentials.
• No variable linked to a widget.

Conclusion

In this tutorial, we learned how to connect a Modbus energy meter to the Arduino Cloud IoT using a MKR WiFi 1010 board and a MKR 485 Shield. We also learned how to visualize the energy meter data in a dashboard using widgets. More tutorials? You can find them in the Arduino Cloud IoT documentation page.