Demo 15: How to build a system to update Price Tag automatically using Arduino ESP32

Tech It Yourself 10:03 AM
1. Introduction
- Imaging you have a mobile store with many mobiles on the shelf. Every mobile has its own price tag. One day you want to update the price tag for them, so it take a lot of time to update price tag for the whole store. In this demo I will show you how to build a system to update price tag automatically using Arduino ESP32. You just sit at one place, open an application, input the new price and click OK.
In order to build this system we will refer:
2. Hardware 
- We will use LCD, OLED to display the Price Tag. First row to display mobile name (iPhone 7). And second row to display the price of it (700USD).
- In this demo we take 2 nodes (2 ESP32 or ESP8266): first node to display the price tag of iPhone and the second node to display price tag of Samsung S8.
- For LCD, we connect like Demo 4
Figure: ESP32 connect to I2C SH1106 OLED
Here we connect:
[ESP32 GPIO12 - LCM1602 SDA]
[ESP32 GPIO14 - LCM1602 SCL]
[ESP32 GND - LCM1602 GND]
[LCM1602 - 5V]
- For OLED, we connect like Demo 6
Figure: ESP32 connect to I2C SH1106 OLED
Here we connect:
[ESP32 3.3V – OLED VCC]
[ESP32 GND – OLED GND]
[ESP32 IO12– OLED SDA]
[ESP32 IO14 – OLED SCL]
3. Software
We apply MQTT for our system. Here is the model:
Figure: Price tag system model using MQTT
- MQTT broker, we use mosquitto
- Two Arduino ESP32 nodes using MQTT library PubSubClient in Demo 14
- For simple demo, I developed the application to update new price in Python and MQTT client library called paho-mqtt.
Figure: Application to update new Price (Python + paho mqtt client)
- Next we define topic: 
update/pricetag/{unique_id_of_product_need_update_price}
For example: update/pricetag/sss8: here the LCD ESP32 node will display the price tag of Samsung S8 and subscribe the topic "update/pricetag/sss8". And the payload of topic is Self-defined "samsung8-800USD". Here "samsung8" is new product name, and "800USD" is new product price. Both are separated by "-".
- Download and install Python DIY
- To install Paho-mqtt, there are 2 ways:
 + Using pip, from command line type: pip install paho-mqtt
 + Download and unzip paho-mqtt, go to unzipped folder and type:  
python setup.py install 
- This library also support standard interfaces of MQTT like subscribe() and publish() (publish single or multiple topic(s))
Here is the code for update price application: pricetag.py
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#this is to overcome Python2/3 version
try:
    #this is style for Python 3 import 
    from  tkinter import *
except ImportError:
    #in case import for Python 3 is error
    #use this for Python 2 import
    from  Tkinter import *
import sys
#similar to comments above
try:
    import paho.mqtt.publish as publish
except ImportError:
    import os
    import inspect
    cmd_subfolder = os.path.realpath(os.path.abspath(os.path.join(os.path.split(inspect.getfile( inspect.currentframe() ))[0],"../src")))
    if cmd_subfolder not in sys.path:
        sys.path.insert(0, cmd_subfolder)
    import paho.mqtt.publish as publish

#for demo I use 2 nodes
data = [   
    ['sss8', 'sss8.gif', 'SamSung S8', '800USD'],
    ['ip7', 'ip7.gif', 'iPhone 7S', '700USD']
]

#this is the simple GUI part
root = Tk()
root.wm_title("PriceTag")
rows = []
img = []
for i in range(2):
    cols = []
    for j in range(4):
        if(j == 1):
            img.append(PhotoImage(file=data[i][j]))
            e = Button(root, image=img[-1])
            e.grid(row=i, column=j, sticky=NSEW)
        elif(j == 0):
            e = Entry(root, relief=RIDGE, justify='center')
            e.grid(row=i, column=j, sticky=NSEW)
            e.insert(END, data[i][j])
            e.config(state=DISABLED)
            cols.append(e)
        else:
            e = Entry(root, relief=RIDGE, justify='center')
            e.grid(row=i, column=j, sticky=NSEW)
            e.insert(END, data[i][j])
            cols.append(e)
    rows.append(cols)
#this function will be invoked when the Update button is clicked
def onUpdate():
    msgs = []
    #we loop through all products and publish new price
    for row in rows:
        #build topic: update/pricetag/sss8 : {'name': 'samsung8', 'value': '800USD'}
        payload = str(row[1].get()) + '-' + str(row[2].get())
        #every topic is stored under dictionary like json
        pair = {'topic':'update/pricetag/'+row[0].get(), 'payload':payload}
        #here we send multiple topics instead of looping through every topic and send
        #so we append multiple topics in a list
        msgs.append(pair);
    #and pass the list of topics to publish.multiple()
    publish.multiple(msgs, hostname="localhost")
    
Button(text='Update', command=onUpdate).grid()
mainloop()
Here is the Arduino code for LCD display: esp32lcdpricetag
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#include <WiFi.h>
#include <PubSubClient.h>
#include <Wire.h> 
#include <LiquidCrystal_I2C.h>

/* change it with your ssid-password */
const char* ssid = "dd-wrt";
const char* password = "0000000000";
/* this is the IP of PC where you installed MQTT Server */
const char* mqtt_server = "192.168.1.103";

/* create an instance of PubSubClient client */
WiFiClient espClient;
PubSubClient client(espClient);
/* this is for LCD */
LiquidCrystal_I2C lcd(0x27,16,2);

/* topics */
#define SSS8_PRICE_TOPIC    "update/pricetag/sss8"

long lastMsg = 0;
char msg[20];

void receivedCallback(char* topic, byte* payload, unsigned int length) {
  Serial.print("Message received: ");
  Serial.println(topic);
  int separate = 0;
  Serial.print("payload: ");
  for (int i = 0; i < length; i++) {
    Serial.print((char)payload[i]);
    /* we parse topic by separator '-'*/
    if(payload[i] == '-'){
      separate = i+1;
      payload[i] = 0;
    }
  }
  lcd.clear();
  lcd.setCursor(0,0);
  lcd.print((char *)payload);
  /* set cursor row 1 col 0 */
  lcd.setCursor(0,1);
  lcd.print((char *)&payload[separate]);
}

void mqttconnect() {
  /* Loop until reconnected */
  while (!client.connected()) {
    Serial.print("MQTT connecting ...");
    /* client ID */
    String clientId = "ESP32Client";
    /* connect now */
    if (client.connect(clientId.c_str())) {
      Serial.println("connected");
      /* subscribe topic */
      client.subscribe(SSS8_PRICE_TOPIC);
    } else {
      Serial.print("failed, status code =");
      Serial.print(client.state());
      Serial.println("try again in 5 seconds");
      /* Wait 5 seconds before retrying */
      delay(5000);
    }
  }
}

void setup() {
  Serial.begin(115200);
  /* initialize the lcd with SDA and SCL pins */
  lcd.begin(12, 14);
  /* Print a message to the LCD.*/
  lcd.backlight();
  /* set cursor row 0 col 0 */
  lcd.setCursor(0,0);
  lcd.print("iotsharing.com");
  /* connect wifi */
  Serial.print("Connecting to ");
  Serial.println(ssid);

  WiFi.begin(ssid, password);

  while (WiFi.status() != WL_CONNECTED) {
    delay(500);
    Serial.print(".");
  }

  Serial.println("");
  Serial.println("WiFi connected");
  Serial.println("IP address: ");
  Serial.println(WiFi.localIP());

  /* configure the MQTT server with IPaddress and port */
  client.setServer(mqtt_server, 1883);
  /* this receivedCallback function will be invoked 
  when client received subscribed topic */
  client.setCallback(receivedCallback);
  
}
void loop() {
  /* if client was disconnected then try to reconnect again */
  if (!client.connected()) {
    mqttconnect();
  }
  /* this function will listen for incomming 
  subscribed topic-process-invoke receivedCallback */
  client.loop();
}
Here is the Arduino code for OLED display: esp32oledpricetag
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#include <WiFi.h>
#include <PubSubClient.h>
#include <Wire.h>
#include <Adafruit_SH1106.h>

#define OLED_SDA 12
#define OLED_SCL 14

Adafruit_SH1106 display(12, 14);
/* change it with your ssid-password */
const char* ssid = "dd-wrt";
const char* password = "0000000000";
/* this is the IP of PC where you installed MQTT Server */
const char* mqtt_server = "192.168.1.103";

/* create an instance of PubSubClient client */
WiFiClient espClient;
PubSubClient client(espClient);

/* topics */
#define IP7_PRICE_TOPIC    "update/pricetag/ip7"

long lastMsg = 0;
char msg[20];
#define BUF_SIZE 100
byte rec[BUF_SIZE];
int separate = 0;
int dispState = 0;
  
void receivedCallback(char* topic, byte* payload, unsigned int length) {
  Serial.println(topic);
  int i = 0;
  Serial.print("payload: ");
  for (i = 0; i < length; i++) {
    Serial.print((char)payload[i]);
    /* we parse topic by separator '-'*/
    if(payload[i] == '-'){
      separate = i+1;
      payload[i] = 0;
    }
    if(i < BUF_SIZE){
      rec[i] = payload[i];
    }
  }
  /*we got data so backup for processing 
  if we have enough buffer size, else ignore msg */
  if(i < BUF_SIZE){
    if(dispState == 0){
      dispState = 1;
    }
  }
}

void mqttconnect() {
  /* Loop until reconnected */
  while (!client.connected()) {
    Serial.print("MQTT connecting ...");
    /* client ID */
    String clientId = "ESP32Client";
    /* connect now */
    if (client.connect(clientId.c_str())) {
      Serial.println("connected");
      /* subscribe topic with QoS 1*/
      client.subscribe(IP7_PRICE_TOPIC, 1);
    } else {
      Serial.print("failed, status code =");
      Serial.print(client.state());
      Serial.println("try again in 5 seconds");
      /* Wait 5 seconds before retrying */
      delay(5000);
    }
  }
}

void setup() {
  Serial.begin(115200);
  /* while flashing sw detach OLED VCC w ESP32 3.3,
  delay here to have enough time to attach 
  OLED VCC with ESP32 3.3 again */
  delay(3000);
  /* initialize oled */
  display.begin(SH1106_SWITCHCAPVCC, 0x3C); 
  display.clearDisplay();
  /* set text size, color, cursor position, 
  set buffer with  Hello world and show off*/
  display.setTextSize(2);
  display.setTextColor(WHITE);
  display.setCursor(2,2);
  display.println("iotsharing.com");
  display.display();
  
  Serial.print("Connecting to ");
  Serial.println(ssid);
  WiFi.begin(ssid, password);

  while (WiFi.status() != WL_CONNECTED) {
    delay(500);
    Serial.print(".");
  }

  Serial.println("");
  Serial.println("WiFi connected");
  Serial.println("IP address: ");
  Serial.println(WiFi.localIP());

  /* configure the MQTT server with IPaddress and port */
  client.setServer(mqtt_server, 1883);
  /* this receivedCallback function will be invoked 
  when client received subscribed topic */
  client.setCallback(receivedCallback);
}
void loop() {
  /* if client was disconnected then try to reconnect again */
  if (!client.connected()) {
    mqttconnect();
  }
  /* this function will listen for incomming 
  subscribed topic-process-invoke receivedCallback */
  client.loop();
  /* because OLED waste time 
  so we use state machine to display 
  step by step every loop */
  switch(dispState)
  {
    case 1:
    display.clearDisplay();
    dispState = 2;
    break;
    case 2:
    display.setCursor(2,2);
    dispState = 3;
    break;
    case 3:
    display.println((char *)rec);
    dispState = 4;
    break;
    case 4:
    display.setCursor(2,22);
    dispState = 5;
    break;
    case 5:
    display.println((char *)&rec[separate]);
    dispState = 6;
    break;
    case 6:
    display.display();
    dispState = 0;
    memset(rec, 0, BUF_SIZE);
    break;
    default:
    break;
  }
}
4. Result
 Figure: auto update price tag

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1 Comments

Selvamani1991 said…
Hi,

ESP32-Mqtt was not connected using Azure SSL Certificate

I am using the below code for connecting with ssl certificate was not working.

#include
const char* ssid = "xxx"; // your network SSID (name of wifi network)
const char* password = "xxx"; // your network password
const char* server = "xxx.azure-devices.net"; // Server URL
const char* test_root_ca=
"-----BEGIN CERTIFICATE-----\n"

"-----END CERTIFICATE-----\n";

// You can use x.509 client certificates if you want
const char* test_client_key =
"-----BEGIN RSA PRIVATE KEY-----\n"

"-----END RSA PRIVATE KEY-----\n"; //to verify the client

const char* test_client_cert =
"-----BEGIN CERTIFICATE-----\n"

"-----END CERTIFICATE-----\n"; //to verify the client
WiFiClientSecure client;
void setup() {
//Initialize serial and wait for port to open:
Serial.begin(115200);
delay(100);
Serial.print("Attempting to connect to SSID: ");
Serial.println(ssid);
WiFi.begin(ssid, password);
// attempt to connect to Wifi network:
while (WiFi.status() != WL_CONNECTED) {
Serial.print(".");
// wait 1 second for re-trying
delay(1000);
}
Serial.print("Connected to ");
Serial.println(ssid);
client.setCACert(test_root_ca);
client.setCertificate(test_client_cert); // for client verification
client.setPrivateKey(test_client_key); // for client verification
Serial.println("\nStarting connection to server...");
if (!client.connect(server, 8883)){
Serial.println("Connection failed!");
}
else {
Serial.println("Connected to server!");
}
}
void loop() {
// do nothing
}
March 10, 2021 at 2:59 AM
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