Help Converting Thinkspeak String to MQTT Strings

I have A water sensor connected to an ESP8266 and an OLED display that currently sends its data both to the display and to ThinkSpeak, now I want to replace ThinkSpeak with MQTT. I need help with converting the ThinkSpeak strings to MQTT strings (lines 203-222 I think). Any help would be appreciated . Here is the code

#include <ESP8266WiFi.h>
#include <PubSubClient.h>
#include <SPI.h>
#include <Wire.h>
#include <Adafruit_GFX.h>
#include <Adafruit_SSD1306.h>
 
#define SCREEN_WIDTH 128    // OLED display width, in pixels
#define SCREEN_HEIGHT 64    // OLED display height, in pixels
#define OLED_RESET -1       // Reset pin # (or -1 if sharing Arduino reset pin)
 
Adafruit_SSD1306 display(SCREEN_WIDTH, SCREEN_HEIGHT, &Wire, OLED_RESET);
 
//WiFi Setup
const char *ssid = "xxxxxxx";     // replace with your wifi ssid and wpa2 key
const char *pass = "xxxxxxxx";     // Enter WiFi password

//MQTT 
const char* mqtt_server = "192.168.0.8";  // IP of the MQTT broker
const char* flowRate_topic = "Farm/GrowTent/RDWCH20Flow";
const char* totalLitres_topic = "Farm/GrowTent/RDWCLitres";
int mqtt_port = 1883;


#define LED_BUILTIN 16
#define SENSOR  2
 
long currentMillis = 0;
long previousMillis = 0;
int interval = 1000;
boolean ledState = LOW;
float calibrationFactor = 4.5;
volatile byte pulseCount;
byte pulse1Sec = 0;
float flowRate;
unsigned long flowMilliLitres;
unsigned int totalMilliLitres;
float flowLitres;
float totalLitres;
 
void IRAM_ATTR pulseCounter()
{
  pulseCount++;
}
 
WiFiClient espClient;
PubSubClient client(espClient);
long lastMsg = 0;
char msg[50];
int value = 0;
 
void setup(){
  Serial.begin(115200);
  display.begin(SSD1306_SWITCHCAPVCC, 0x3C); //initialize with the I2C addr 0x3C (128x64)
  display.clearDisplay();
  delay(10);
 
  pinMode(LED_BUILTIN, OUTPUT);
  pinMode(SENSOR, INPUT_PULLUP);
 
  pulseCount = 0;
  flowRate = 0.0;
  flowMilliLitres = 0;
  totalMilliLitres = 0;
  previousMillis = 0;
 
  attachInterrupt(digitalPinToInterrupt(SENSOR), pulseCounter, FALLING);
  sensors.begin();
 
 setup_wifi();
 client.setServer(mqtt_server, mqtt_port);
 client.setCallback(callback);

 Serial.println("Connected ");
 Serial.print("MQTT Server ");
 Serial.print(mqtt_server);
 Serial.print(":");
 Serial.println(String(mqtt_port)); 
 Serial.print("ESP8266 IP ");
 Serial.println(WiFi.localIP()); 
 Serial.println("Modbus RTU Master Online");
}
void setup_wifi() {

 delay(10);
 // We start by connecting to a WiFi network
 Serial.println();
 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());
}

void callback(char* topic, byte* payload, unsigned int length) {
 Serial.print("Message arrived [");
 Serial.print(topic);
 Serial.print("] ");
 for (int i = 0; i &lt; length; i++) {
 Serial.print((char)payload[i]);
 }
 Serial.println();
 
}

void reconnect() {
 // Loop until we're reconnected
 while (!client.connected()) {
 Serial.print("Attempting MQTT connection...");
 // Attempt to connect
 if (client.connect("ESP8266Client")) {

 Serial.println("connected");
 // client.subscribe("event");
 } else {
 Serial.print("failed, rc=");
 Serial.print(client.state());
 Serial.println(" try again in 5 seconds");
 // Wait 5 seconds before retrying
 delay(5000);
 }
 }
} 
// End MQTT Stuff
void loop()
{
  currentMillis = millis();
  if (currentMillis - previousMillis > interval) 
  {
    
    pulse1Sec = pulseCount;
    pulseCount = 0;
 
    // Because this loop may not complete in exactly 1 second intervals we calculate
    // the number of milliseconds that have passed since the last execution and use
    // that to scale the output. We also apply the calibrationFactor to scale the output
    // based on the number of pulses per second per units of measure (litres/minute in
    // this case) coming from the sensor.
    flowRate = ((1000.0 / (millis() - previousMillis)) * pulse1Sec) / calibrationFactor;
    previousMillis = millis();
 
    // Divide the flow rate in litres/minute by 60 to determine how many litres have
    // passed through the sensor in this 1 second interval, then multiply by 1000 to
    // convert to millilitres.
    flowMilliLitres = (flowRate / 60) * 1000;
    flowLitres = (flowRate / 60);
 
    // Add the millilitres passed in this second to the cumulative total
    totalMilliLitres += flowMilliLitres;
    totalLitres += flowLitres;
    
    // Print the flow rate for this second in litres / minute
    Serial.print("Flow rate: ");
    Serial.print(float(flowRate));  // Print the integer part of the variable
    Serial.print("L/min");
    Serial.print("\t");       // Print tab space
 
    display.clearDisplay();
    
    display.setCursor(10,0);  //oled display
    display.setTextSize(1);
    display.setTextColor(WHITE);
    display.print("Water Flow Meter");
    
    display.setCursor(0,20);  //oled display
    display.setTextSize(2);
    display.setTextColor(WHITE);
    display.print("R:");
    display.print(float(flowRate));
    display.setCursor(100,28);  //oled display
    display.setTextSize(1);
    display.print("L/M");
 
    // Print the cumulative total of litres flowed since starting
    Serial.print("Output Liquid Quantity: ");
    Serial.print(totalMilliLitres);
    Serial.print("mL / ");
    Serial.print(totalLitres);
    Serial.println("L");
 
    display.setCursor(0,45);  //oled display
    display.setTextSize(2);
    display.setTextColor(WHITE);
    display.print("V:");
    display.print(totalLitres);
    display.setCursor(100,53);  //oled display
    display.setTextSize(1);
    display.print("L");
    display.display();
  }
// Need to convert the below to Send to MQTT insted of think Speak  
   //if (client.connect(server, 80)) // "184.106.153.149" or api.thingspeak.com
   if (client.connect("ESP8266Client"))
    {
    String postStr = apiKey;
      postStr += "&field1=";
      postStr += String(float(flowRate));
      postStr += "&field2=";
      postStr += String(totalLitres);
      postStr += "\r\n\r\n";
    
    client.print("POST /update HTTP/1.1\n");
    client.print("Host: api.thingspeak.com\n");
    client.print("Connection: close\n");
    client.print("X-THINGSPEAKAPIKEY: " + apiKey + "\n");
    client.print("Content-Type: application/x-www-form-urlencoded\n");
    client.print("Content-Length: ");
    client.print(postStr.length());
    client.print("\n\n");
    client.print(postStr);
   
  }
    client.stop();
}

I see you don't need no username , user password to initiate mqtt conn.

you need some script or something on broker side to 'receive' the data 'sent' by your ESP

start with this one

Thanks for your replay I have updated my code per your suggestion. I still need help with lines 208 - 228 getting the data into MQTT instead of Thingspeak

/*
 Basic ESP8266 MQTT example
 Water Fall Sensor Diplay to OLED & MQTT
 MQTT Data will be Visualize with InfluxDB and Grafana
*/

#include <ESP8266WiFi.h>
#include <PubSubClient.h>
#include <SPI.h>
#include <Wire.h>
#include <Adafruit_GFX.h>
#include <Adafruit_SSD1306.h>
//OLED Define
#define SCREEN_WIDTH 128    // OLED display width, in pixels
#define SCREEN_HEIGHT 64    // OLED display height, in pixels
#define OLED_RESET -1       // Reset pin # (or -1 if sharing Arduino reset pin)
 
Adafruit_SSD1306 display(SCREEN_WIDTH, SCREEN_HEIGHT, &Wire, OLED_RESET);
// WiFi Setup.
const char* ssid = "........";
const char* password = "........";

//MQTT 
const char* mqtt_server = "192.168.15.x";
const char* flowRate_topic = "Farm/GrowTent/RDWCH20Flow";
const char* totalLitres_topic = "Farm/GrowTent/RDWCLitres";
int mqtt_port = 1883;

//More OLED
#define LED_BUILTIN 16
#define SENSOR  2
 
long currentMillis = 0;
long previousMillis = 0;
int interval = 1000;
boolean ledState = LOW;
float calibrationFactor = 4.5;
volatile byte pulseCount;
byte pulse1Sec = 0;
float flowRate;
unsigned long flowMilliLitres;
unsigned int totalMilliLitres;
float flowLitres;
float totalLitres;
 
void IRAM_ATTR pulseCounter()
{
  pulseCount++;
}

WiFiClient espClient;
PubSubClient client(espClient);
unsigned long lastMsg = 0;
#define MSG_BUFFER_SIZE	(50)
char msg[MSG_BUFFER_SIZE];
int value = 0;

void setup_wifi() {

  delay(10);
  // We start by connecting to a WiFi network
  Serial.println();
  Serial.print("Connecting to ");
  Serial.println(ssid);

  WiFi.mode(WIFI_STA);
  WiFi.begin(ssid, password);

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

  randomSeed(micros());

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

void callback(char* topic, byte* payload, unsigned int length) {
  Serial.print("Message arrived [");
  Serial.print(topic);
  Serial.print("] ");
  for (int i = 0; i < length; i++) {
    Serial.print((char)payload[i]);
  }
  Serial.println();

  // Switch on the LED if an 1 was received as first character
  if ((char)payload[0] == '1') {
    digitalWrite(BUILTIN_LED, LOW);   // Turn the LED on (Note that LOW is the voltage level
    // but actually the LED is on; this is because
    // it is active low on the ESP-01)
  } else {
    digitalWrite(BUILTIN_LED, HIGH);  // Turn the LED off by making the voltage HIGH
  }

}

void reconnect() {
 // Loop until we're reconnected
 while (!client.connected()) {
 Serial.print("Attempting MQTT connection...");
 // Attempt to connect
 if (client.connect("ESP8266Client")) {

 Serial.println("connected");
 // client.subscribe("event");
 } else {
 Serial.print("failed, rc=");
 Serial.print(client.state());
 Serial.println(" try again in 5 seconds");
 // Wait 5 seconds before retrying
 delay(5000);
 }
 }
}
//Sensor Stuff
void setup()
{
  Serial.begin(115200);
  display.begin(SSD1306_SWITCHCAPVCC, 0x3C); //initialize with the I2C addr 0x3C (128x64)
  display.clearDisplay();
  delay(10);
 
  pinMode(LED_BUILTIN, OUTPUT);
  pinMode(SENSOR, INPUT_PULLUP);
 
  pulseCount = 0;
  flowRate = 0.0;
  flowMilliLitres = 0;
  totalMilliLitres = 0;
  previousMillis = 0;
 
  attachInterrupt(digitalPinToInterrupt(SENSOR), pulseCounter, FALLING);
}
 
void loop()
{
  currentMillis = millis();
  if (currentMillis - previousMillis > interval) 
  {
    
    pulse1Sec = pulseCount;
    pulseCount = 0;
 
    // Because this loop may not complete in exactly 1 second intervals we calculate
    // the number of milliseconds that have passed since the last execution and use
    // that to scale the output. We also apply the calibrationFactor to scale the output
    // based on the number of pulses per second per units of measure (litres/minute in
    // this case) coming from the sensor.
    flowRate = ((1000.0 / (millis() - previousMillis)) * pulse1Sec) / calibrationFactor;
    previousMillis = millis();
 
    // Divide the flow rate in litres/minute by 60 to determine how many litres have
    // passed through the sensor in this 1 second interval, then multiply by 1000 to
    // convert to millilitres.
    flowMilliLitres = (flowRate / 60) * 1000;
    flowLitres = (flowRate / 60);
 
    // Add the millilitres passed in this second to the cumulative total
    totalMilliLitres += flowMilliLitres;
    totalLitres += flowLitres;
    
    // Print the flow rate for this second in litres / minute
    Serial.print("Flow rate: ");
    Serial.print(float(flowRate));  // Print the integer part of the variable
    Serial.print("L/min");
    Serial.print("\t");       // Print tab space
 
    display.clearDisplay();
    
    display.setCursor(10,0);  //oled display
    display.setTextSize(1);
    display.setTextColor(WHITE);
    display.print("Water Flow Meter");
    
    display.setCursor(0,20);  //oled display
    display.setTextSize(2);
    display.setTextColor(WHITE);
    display.print("R:");
    display.print(float(flowRate));
    display.setCursor(100,28);  //oled display
    display.setTextSize(1);
    display.print("L/M");
 
    // Print the cumulative total of litres flowed since starting
    Serial.print("Output Liquid Quantity: ");
    Serial.print(totalMilliLitres);
    Serial.print("mL / ");
    Serial.print(totalLitres);
    Serial.println("L");
 
    display.setCursor(0,45);  //oled display
    display.setTextSize(2);
    display.setTextColor(WHITE);
    display.print("V:");
    display.print(totalLitres);
    display.setCursor(100,53);  //oled display
    display.setTextSize(1);
    display.print("L");
    display.display();
  }
// Need to convert the below to Send to MQTT insted of think Speak  
    
  if (client.connect(server, 80)) // "184.106.153.149" or api.thingspeak.com
  {
    String postStr = apiKey;
      postStr += "&field1=";
      postStr += String(float(flowRate));
      postStr += "&field2=";
      postStr += String(totalLitres);
      postStr += "\r\n\r\n";
    
    client.print("POST /update HTTP/1.1\n");
    client.print("Host: api.thingspeak.com\n");
    client.print("Connection: close\n");
    client.print("X-THINGSPEAKAPIKEY: " + apiKey + "\n");
    client.print("Content-Type: application/x-www-form-urlencoded\n");
    client.print("Content-Length: ");
    client.print(postStr.length());
    client.print("\n\n");
    client.print(postStr);
   
  }
    client.stop();
}

Notes:

Your spaghettis code is a bit difficult to follow, but I don't see where you are connecting to the broker. You need void reconnect() at the top of the loop.

Use MQTTExplorer to monitor the data being published.

The data to publish is a const char.

Here is a project of mine that publishes my freezer temperature on MQTT every ten seconds. It may give you some hints.

Sorry for the confusion, I tried to convert the original code myself while trying to teach myself. Here is the original code

#include <ESP8266WiFi.h>
#include <SPI.h>
#include <Wire.h>
#include <Adafruit_GFX.h>
#include <Adafruit_SSD1306.h>
 
#define SCREEN_WIDTH 128    // OLED display width, in pixels
#define SCREEN_HEIGHT 64    // OLED display height, in pixels
#define OLED_RESET -1       // Reset pin # (or -1 if sharing Arduino reset pin)
 
Adafruit_SSD1306 display(SCREEN_WIDTH, SCREEN_HEIGHT, &Wire, OLED_RESET);
 
String apiKey = "xxxxxxxxxxxxxxxxxxxxxxxxx; // Enter your Write API key from ThingSpeak
const char *ssid = "xxxxxxxx";     // replace with your wifi ssid and wpa2 key
const char *pass = "xxxxxx";
const char* server = "api.thingspeak.com";
 
#define LED_BUILTIN 16
#define SENSOR  2
 
long currentMillis = 0;
long previousMillis = 0;
int interval = 1000;
boolean ledState = LOW;
float calibrationFactor = 4.5;
volatile byte pulseCount;
byte pulse1Sec = 0;
float flowRate;
unsigned long flowMilliLitres;
unsigned int totalMilliLitres;
float flowLitres;
float totalLitres;
 
void IRAM_ATTR pulseCounter()
{
  pulseCount++;
}
 
WiFiClient client;
 
void setup()
{
  Serial.begin(115200);
  display.begin(SSD1306_SWITCHCAPVCC, 0x3C); //initialize with the I2C addr 0x3C (128x64)
  display.clearDisplay();
  delay(10);
 
  pinMode(LED_BUILTIN, OUTPUT);
  pinMode(SENSOR, INPUT_PULLUP);
 
  pulseCount = 0;
  flowRate = 0.0;
  flowMilliLitres = 0;
  totalMilliLitres = 0;
  previousMillis = 0;
 
  attachInterrupt(digitalPinToInterrupt(SENSOR), pulseCounter, FALLING);
}
 
void loop()
{
  currentMillis = millis();
  if (currentMillis - previousMillis > interval) 
  {
    
    pulse1Sec = pulseCount;
    pulseCount = 0;
 
    // Because this loop may not complete in exactly 1 second intervals we calculate
    // the number of milliseconds that have passed since the last execution and use
    // that to scale the output. We also apply the calibrationFactor to scale the output
    // based on the number of pulses per second per units of measure (litres/minute in
    // this case) coming from the sensor.
    flowRate = ((1000.0 / (millis() - previousMillis)) * pulse1Sec) / calibrationFactor;
    previousMillis = millis();
 
    // Divide the flow rate in litres/minute by 60 to determine how many litres have
    // passed through the sensor in this 1 second interval, then multiply by 1000 to
    // convert to millilitres.
    flowMilliLitres = (flowRate / 60) * 1000;
    flowLitres = (flowRate / 60);
 
    // Add the millilitres passed in this second to the cumulative total
    totalMilliLitres += flowMilliLitres;
    totalLitres += flowLitres;
    
    // Print the flow rate for this second in litres / minute
    Serial.print("Flow rate: ");
    Serial.print(float(flowRate));  // Print the integer part of the variable
    Serial.print("L/min");
    Serial.print("\t");       // Print tab space
 
    display.clearDisplay();
    
    display.setCursor(10,0);  //oled display
    display.setTextSize(1);
    display.setTextColor(WHITE);
    display.print("Water Flow Meter");
    
    display.setCursor(0,20);  //oled display
    display.setTextSize(2);
    display.setTextColor(WHITE);
    display.print("R:");
    display.print(float(flowRate));
    display.setCursor(100,28);  //oled display
    display.setTextSize(1);
    display.print("L/M");
 
    // Print the cumulative total of litres flowed since starting
    Serial.print("Output Liquid Quantity: ");
    Serial.print(totalMilliLitres);
    Serial.print("mL / ");
    Serial.print(totalLitres);
    Serial.println("L");
 
    display.setCursor(0,45);  //oled display
    display.setTextSize(2);
    display.setTextColor(WHITE);
    display.print("V:");
    display.print(totalLitres);
    display.setCursor(100,53);  //oled display
    display.setTextSize(1);
    display.print("L");
    display.display();
  }

    
  if (client.connect(server, 80)) // "184.106.153.149" or api.thingspeak.com
  {
    String postStr = apiKey;
      postStr += "&field1=";
      postStr += String(float(flowRate));
      postStr += "&field2=";
      postStr += String(totalLitres);
      postStr += "\r\n\r\n";
    
    client.print("POST /update HTTP/1.1\n");
    client.print("Host: api.thingspeak.com\n");
    client.print("Connection: close\n");
    client.print("X-THINGSPEAKAPIKEY: " + apiKey + "\n");
    client.print("Content-Type: application/x-www-form-urlencoded\n");
    client.print("Content-Length: ");
    client.print(postStr.length());
    client.print("\n\n");
    client.print(postStr);
   
  }
    client.stop();
}