MQTT subscription - mqtt

Question

Can someone help me with this code?
The goal is to trigger a Led when the value of the payload is > 1000.
It is a MQTT subscribtion code based on the esp8266mqtt PubSub client example. I will use it for a subscribyion of a topic from a CO2sensor
I've tried to modify a part of it but I think it has yo do something with the kind of datatype or a wrong condition?
#include <ESP8266WiFi.h>
#include <PubSubClient.h>
// Update these with values suitable for your network.
const char *ssid = "xxx";
const char *password = "xxx";
const char *mqtt_server = "xxxx";
WiFiClient espClient;
PubSubClient client(espClient);
long lastMsg = 0;
char msg[50];
int value = 0;
int led = D4;
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(".");
}
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 value of C02 is above 1000
i = atoi (payload); //convert string to integer
if ( i > 1000) // comparison
{
digitalWrite(led, HIGH); // Turn the LED on
}
else
{
digitalWrite(led, LOW); // Turn the LED off
}
}
void reconnect()
{
// Loop until we're reconnected
while (!client.connected())
{
Serial.print("Attempting MQTT connection...");
// Create a random client ID
String clientId = "ESP8266Client-";
clientId += String(random(0xffff), HEX);
// Attempt to connect
if (client.connect(clientId.c_str()))
{
Serial.println("connected");
// Once connected, publish an announcement...
//client.publish("outTopic", "Test");
// ... and resubscribe
client.subscribe("my/sensors/co2");
}
else
{
Serial.print("failed, rc=");
Serial.print(client.state());
Serial.println(" try again in 5 seconds");
// Wait 5 seconds before retrying
delay(5000);
}
}
}
void setup()
{
pinMode(led, OUTPUT); // Initialize the BUILTIN_LED pin as an output
Serial.begin(115200);
setup_wifi();
client.setServer(mqtt_server, 1883);
client.setCallback(callback);
}
void loop()
{
if (!client.connected())
{
reconnect();
}
client.loop();
}
Kind regards
Hi, This is what I publish:
void pubMessage() {
char message[16];
snprintf(message, sizeof(message), "%d", co2);
client.publish("my/sensors/co2", message);
delay(30000);

Answer 1

First you are casting the first byte of payload to a char.
Since it's just the first byte, it has a max value of 256.
Second you are comparing that 1 bytes value to the string '1000'
Without knowing exactly what you are publishing it is very hard to tell you how to fix it.
If you are publishing a string representing the number then you will need to parse it first with atoi() then do the comparison to the integer 1000 not the string.
If it is a byte value then you will need to read the correct value from the incoming byte array before doing the comparison.