Send the data to one MQTT topic using JSON

platformio.ini

@@ -16,3 +16,4 @@ lib_deps =
   adafruit/DHT sensor library@^1.4.4
   adafruit/Adafruit Unified Sensor@^1.1.9
   knolleary/PubSubClient@^2.8
+  bblanchon/ArduinoJson@^6.21.1

src/main.cpp

@@ -7,15 +7,11 @@
 DHT dht(DHTPIN, DHTTYPE);
 
 const int fc28_pin = A0;
-// TODO Tweak threshold to get good value
-const int soil_threshold = 40;
-const int num_topics = 3;
 const int max_connection_attempts = 60;
-const char *topics[] = {"homeostasis/temperature", "homeostasis/humidity",
-                        "homeostasis/soil_humidity"};
+const char *topic = "homeostasis/room";
 const char *device_id = "homeostasis";
-WiFiClient wlan_client;
-PubSubClient mqtt_client(wlan_client);
+WiFiClient wifi_client;
+PubSubClient mqtt_client(wifi_client);
 
 bool check_valid_value(float value) {
   return (!isnan(value) && value >= 0 && value <= 100);
@@ -32,10 +28,10 @@ void loop() {
   float humidity = dht.readHumidity();
   int analog_val = analogRead(fc28_pin);
   int soil_percentage = map(analog_val, 0, 1023, 0, 100);
-  float data[] = {temperature, humidity, static_cast<float>(soil_percentage)};
+  float data[3] = {temperature, humidity, static_cast<float>(soil_percentage)};
   if (check_valid_value(temperature) && check_valid_value(humidity)) {
-    mqtt_transfer(mqtt_client, device_id, topics, data, num_topics);
+    mqtt_transfer(mqtt_client, device_id, topic, data);
   }
-  disconnect_mqtt(mqtt_client, topics, num_topics);
+  disconnect_mqtt(mqtt_client, topic);
   enter_deep_sleep(false);
 }

src/wlan.cpp

@@ -1,5 +1,6 @@
 #include "wlan.h"
 #include "credentials.h"
+#include <ArduinoJson.h>
 
 void initial_connection() {
   WiFi.begin(SSID, PSK);
@@ -23,32 +24,36 @@ void connect_wlan(const int max_retries) {
 }
 
 void connect_mqtt(PubSubClient &client, const char *device_id,
-                  const char **topics, int num_topics) {
+                  const char *topic) {
   if (!client.connected())
     client.setServer(MQTT_HOST, MQTT_PORT);
   if (client.connect(device_id, MQTT_USER, MQTT_PASSWORD)) {
     Serial.println("MQTT connected");
-    for (int i = 0; i < num_topics; i++)
-      client.subscribe(topics[i]);
+    client.subscribe(topic);
   }
 }
 
-void disconnect_mqtt(PubSubClient &client, const char **topics,
-                     int num_topics) {
+void disconnect_mqtt(PubSubClient &client, const char *topic) {
   Serial.println("Disconnecting MQTT");
-  for (int i = 0; i < num_topics; i++)
-    client.unsubscribe(topics[i]);
+  client.unsubscribe(topic);
   client.disconnect();
 }
 
-void mqtt_transfer(PubSubClient &client, const char *device_id,
-                   const char **topics, float *data, int num_topics) {
-  connect_mqtt(client, device_id, topics, num_topics);
-  for (int i = 0; i < num_topics; i++) {
-    char buffer[50];
-    sprintf(buffer, "%f", data[i]);
-    client.publish(topics[i], buffer);
+size_t construct_json(float *data, char *buffer, int buffer_size) {
+  StaticJsonDocument<100> json;
+  json["temperature"] = data[0];
+  json["humidity"] = data[1];
+  json["soil_humidity"] = data[2];
+  size_t payload_size = serializeJson(json, buffer, buffer_size);
+  return payload_size;
 }
+
+void mqtt_transfer(PubSubClient &client, const char *device_id,
+                   const char *topic, float *data) {
+  char buffer[100];
+  connect_mqtt(client, device_id, topic);
+  size_t payload_size = construct_json(data, buffer, 100);
+  client.publish(topic, buffer, payload_size);
   Serial.println("Data transferred successfully");
 }
 

src/wlan.h

@@ -10,10 +10,11 @@ const int WIFI_TIMEOUT = 10000;
 void initial_connection();
 void connect_wlan(const int max_retries);
 void connect_mqtt(PubSubClient &client, const char *device_id,
-                  const char **topics, int num_topics);
-void disconnect_mqtt(PubSubClient &client, const char **topics, int num_topics);
+                  const char *topic);
+void disconnect_mqtt(PubSubClient &client, const char *topic);
+size_t construct_json(float *data, char *buffer, int buffer_size);
 void mqtt_transfer(PubSubClient &client, const char *device_id,
-                   const char **topics, float *data, int num_topics);
+                   const char *topic, float *data);
 void enter_deep_sleep(bool wifi_timeout);
 
 #endif /* WLAN_H */