Comparison of a string received from MQTT/Cloud/Arduino

Question

I am trying to compare the string of data which I am receiving from the MQTT broker. If I receive the keyword faster I want to print "increase motor speed" and when I get slower keyword or any other keyword, I want to print "decrease motor speed". I am not sure how to store the data I receive from mqttClient.read()and then store it in string to then compare it Below is the snippet of the code where I have added it and it seems not to work correctly in my case. can you look at it and let me know what is the mistake?

while (mqttClient.available()) {
Serial.print((char)mqttClient.read());
String ipstring= String("(char)mqttClient.read()");
String fast ="faster";
if((char)mqttClient.read()==fast)
{
Serial.println("increase motor speed");}
else
{
Serial.println("decrease motor speed");
}*
}

I have also attached the code for reference. Thank you!

/*
 Azure IoT Hub NB
 This sketch securely connects to an Azure IoT Hub using MQTT over NB IoT/LTE Cat M1.
 It uses a private key stored in the ATECC508A and a self signed public
 certificate for SSL/TLS authetication.
 It publishes a message every 5 seconds to "devices/{deviceId}/messages/events/" topic
 and subscribes to messages on the "devices/{deviceId}/messages/devicebound/#"
 topic.
 The circuit:
 - MKR NB 1500 board
 - Antenna
 - SIM card with a data plan
 - LiPo battery
 The following tutorial on Arduino Project Hub can be used
 to setup your Azure account and the MKR board:
 https://create.arduino.cc/projecthub/Arduino_Genuino/securely-connecting-an-arduino-nb-1500-to-azure-iot-hub-af6470
 This example code is in the public domain.
*/
#include <ArduinoBearSSL.h>
#include <ArduinoECCX08.h>
#include <utility/ECCX08SelfSignedCert.h>
#include <ArduinoMqttClient.h>
#include <MKRNB.h>
#include "arduino_secrets.h"
int sensorValue;
/////// Enter your sensitive data in arduino_secrets.h
const char pinnumber[] = SECRET_PINNUMBER;
const char broker[] = SECRET_BROKER;
String deviceId = SECRET_DEVICE_ID;
NB nbAccess;
GPRS gprs;
NBClient nbClient; // Used for the TCP socket connection
BearSSLClient sslClient(nbClient); // Used for SSL/TLS connection, integrates with ECC508
MqttClient mqttClient(sslClient);
unsigned long lastMillis = 0;
void setup() {
 Serial.begin(9600);
 while (!Serial);
 if (!ECCX08.begin()) {
 Serial.println("No ECCX08 present!");
 while (1);
 }
 // reconstruct the self signed cert
 ECCX08SelfSignedCert.beginReconstruction(0, 8);
 ECCX08SelfSignedCert.setCommonName(ECCX08.serialNumber());
 ECCX08SelfSignedCert.endReconstruction();
 // Set a callback to get the current time
 // used to validate the servers certificate
 ArduinoBearSSL.onGetTime(getTime);
 // Set the ECCX08 slot to use for the private key
 // and the accompanying public certificate for it
 sslClient.setEccSlot(0, ECCX08SelfSignedCert.bytes(), ECCX08SelfSignedCert.length());
 // Set the client id used for MQTT as the device id
 mqttClient.setId(deviceId);
 // Set the username to "<broker>/<device id>/api-version=2018年06月30日" and empty password
 String username;
 username += broker;
 username += "/";
 username += deviceId;
 username += "/api-version=2018年06月30日";
 mqttClient.setUsernamePassword(username, "");
 // Set the message callback, this function is
 // called when the MQTTClient receives a message
 mqttClient.onMessage(onMessageReceived);
}
void loop() {
 if (nbAccess.status() != NB_READY || gprs.status() != GPRS_READY) {
 connectNB();
 }
 if (!mqttClient.connected()) {
 // MQTT client is disconnected, connect
 connectMQTT();
 }
 // poll for new MQTT messages and send keep alives
 mqttClient.poll();
 // publish a message roughly every 5 seconds.
 if (millis() - lastMillis > 5000) {
 lastMillis = millis();
 publishMessage();
 }
}
unsigned long getTime() {
 // get the current time from the cellular module
 return nbAccess.getTime();
}
void connectNB() {
 Serial.println("Attempting to connect to the cellular network");
 while ((nbAccess.begin(pinnumber) != NB_READY) ||
 (gprs.attachGPRS() != GPRS_READY)) {
 // failed, retry
 Serial.print(".");
 delay(1000);
 }
 Serial.println("You're connected to the cellular network");
 Serial.println();
}
void connectMQTT() {
 Serial.print("Attempting to MQTT broker: ");
 Serial.print(broker);
 Serial.println(" ");
 while (!mqttClient.connect(broker, 8883)) {
 // failed, retry
 Serial.print(".");
 Serial.println(mqttClient.connectError());
 delay(5000);
 }
 Serial.println();
 Serial.println("You're connected to the MQTT broker");
 Serial.println();
 // subscribe to a topic
 mqttClient.subscribe("devices/" + deviceId + "/messages/devicebound/#");
}
void publishMessage() {
 Serial.println("Publishing message");
 // send message, the Print interface can be used to set the message contents
 mqttClient.beginMessage("devices/" + deviceId + "/messages/events/");
 mqttClient.print("hello ");
 sensorValue = analogRead(A0);
 mqttClient.println(sensorValue);
 //mqttClient.print(millis());
 
 mqttClient.endMessage();
}
void onMessageReceived(int messageSize) {
 // we received a message, print out the topic and contents
 Serial.print("Received a message with topic '");
 Serial.print(mqttClient.messageTopic());
 Serial.print("', length ");
 Serial.print(messageSize);
 Serial.println(" bytes:");
 // use the Stream interface to print the contents
 while (mqttClient.available()) {
 Serial.print((char)mqttClient.read());
 String ipstring= String("(char)mqttClient.read()");
 String fast ="faster";
 if((char)mqttClient.read()==fast)
 {
 Serial.println("increase motor speed");}
 else
 {
 Serial.println("decrease motor speed");
 }
 }
 Serial.println();
 Serial.println();
}

• Juraj: Comments are not for extended discussion; this conversation has been moved to chat.

Answer 1

As I read the comments, I see the project requirements are evolving. The 0 = Off command structure will severely limit what you can do, but it is a good starting point.

Regarding the first block of code starting with while (mqttClient.available()) {, then adding your one digit / char commands idea, I have this test sketch for you to try.

You don't need the String object to accomplish your goal. You may have to do something like this though input = (char)mqttClient.read() where the test sketch uses this input = Serial.read();.

char input;
void setup(){
 Serial.begin(9600);
}
void loop(){
 if(Serial.available() > 0){
 input = Serial.read();
 if(input == '0'){
 Serial.println("Turn Off");
 }
 else if(input == '1'){
 Serial.println("Turn On");
 }
 else if(input == '2'){
 Serial.println("Decrease Speed");
 }
 else if(input == '3'){
 Serial.println("Increase Speed");
 }
 }
}

To take it a step further, let's say you want to send commands that start with a single letter, then after the letter, the remaining digits, or chars have a purpose, if you want them to. For example, lets say you send the following command d50. The d could mean decrease speed, and the 50 could mean 50%, 50 steps, etc.

The following test sketch illustrates my point.

char inputBuffer[64 + 1];
void setup(){
 Serial.begin(9600);
}
void loop(){
 while(Serial.available() > 0){
 Serial.readBytesUntil('\n', inputBuffer, sizeof(inputBuffer));
 if(inputBuffer[0] == 'f'){
 Serial.println("Letter 'f' entered");
 }
 // Letter "r". Everything after the "r" should be digits.
 else if(inputBuffer[0] == 'r'){
 Serial.print("Letter 'r' entered\t");
 // Change the letter "r" to the digit 0 to keep atol() happy.
 inputBuffer[0] = B110000;
 Serial.print("Number entered = ");
 Serial.println(atol(inputBuffer));
 // Your code here that uses the number parsed using atol().
 }
 // Letter "s". Everything after the "s" should have a max
 // length of up to 64 chars long for a 64 + 1 char buffer.
 else if(inputBuffer[0] == 's'){
 // MAX CHARS example with a 64 byte buffer:
 // s123456789a123456789b123456789c123456789d123456789e123456789f + CR + NL
 Serial.print("Letter 's' entered\tText entered = ");
 // Print out the chars in the buffer.
 for(int i = 1; i < strlen(inputBuffer); i++){
 Serial.print(inputBuffer[i]);
 }
 Serial.println();
 // Your code here that uses the char data after the letter "s" is entered.
 }
 memset(inputBuffer, 0, sizeof(inputBuffer));
 }
}