Issue #93 adds a check on the battery level

batteries_charger/mqtt_power_supply_manager/mqtt_power_supply_manager.ino

+#include <ESP8266WiFi.h> // Import ESP8266 WiFi library
+#include <PubSubClient.h>// Import PubSubClient library to initialize MQTT protocol
+#include <Adafruit_MCP23X17.h>
+
+// Update these with values suitable for your network.
+
+const char* ssid = "raspi-webgui";//use your ssid
+const char* password = "ChangeMe";//use your password
+const char* mqtt_server = "ohmpy.umons.ac.be";
+const char* mqtt_user = "mqtt_user";
+const char* mqtt_password = "mqtt_password";
+const float conversion_factor = 0.01289; /* use 1MOhm resistor on pin A0 for a max voltage of 13.2V */
+const char* cmd_on = "On";
+const char* cmd_off = "Off";
+const int battery_check_interval = 300000;
+const float min_voltage = 11.5;
+
+WiFiClient espClient;
+PubSubClient client(espClient);
+Adafruit_MCP23X17 mcp;
+
+#define MSG_BUFFER_SIZE  (50)
+#define analogPin A0 /* ESP8266 Analog Pin ADC0 = A0 */
+#define CHARGER_PIN 0
+#define LOAD_PIN 1
+#define D1 5
+#define D2 4
+
+unsigned long lastMsg = 0;
+char msg[MSG_BUFFER_SIZE];
+int adcValue = 0;  /* Variable to store Output of ADC */
+float voltage = 0.0;
+int use_mcp = 0;
+int power_saving_mode = 0;
+unsigned long lastBatteryCheck = 0;
+
+void setup_mcp() {
+  if (!mcp.begin_I2C()) {
+    Serial.println("No I2C!");
+    while (1);
+  }
+  mcp.pinMode(CHARGER_PIN, OUTPUT);
+  mcp.pinMode(LOAD_PIN, OUTPUT);  
+}
+
+void setup_no_mcp() {
+  pinMode(D1, OUTPUT);
+  pinMode(D2, OUTPUT);
+}
+
+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());
+}
+
+// Check for Message received on define topic for MQTT Broker
+void callback(char* topic, byte* payload, unsigned int length) {
+  char cmd[length+1];
+  memcpy(cmd, payload, length);
+  cmd[length] = '\0';
+ 
+  Serial.print("Message arrived [");
+  Serial.print(topic);
+  Serial.print("] ");
+  Serial.print(cmd);
+  Serial.println();
+
+  
+  // Switch relays according to commands (pay attention to the wiring of the relay card
+  
+  if (length == 2 && memcmp(payload, "On", 2) == 0) {
+    digitalWrite(LED_BUILTIN, LOW); // Turn the D1 LED on, the load off then the charger on
+    
+    if( use_mcp == 1 ){
+      mcp.digitalWrite(LOAD_PIN, LOW);
+      delay(250);
+      mcp.digitalWrite(CHARGER_PIN, HIGH);
+    }
+    else {
+      digitalWrite(D2, LOW);
+      delay(250);
+      digitalWrite(D1, HIGH);
+    }
+    
+    
+  } else if (length == 3 && memcmp(payload, "Off", 3) == 0) {
+
+    if( use_mcp == 1 ){
+      mcp.digitalWrite(LED_BUILTIN, HIGH);  // Turn the D1 LED off, the charger off then the load on
+      mcp.digitalWrite(CHARGER_PIN, LOW);
+      delay(250);
+      mcp.digitalWrite(LOAD_PIN, HIGH);
+    }
+    else{
+      digitalWrite(LED_BUILTIN, HIGH);  // Turn the D1 LED off, the charger off then the load on
+      digitalWrite(D1, LOW);
+      delay(250);
+      digitalWrite(D2, HIGH);
+    } 
+    
+  } else if (length == 12 && memcmp(payload, "Read voltage", 12) == 0) {
+    unsigned long now = millis();
+    if (now - lastMsg > 2000) {
+      lastMsg = now;
+
+      read_voltage(); 
+      
+      /* Print the output in the Serial Monitor */
+      Serial.print("ADC Value = ");
+      Serial.print(voltage);
+      Serial.println(" V");
+      snprintf (msg, MSG_BUFFER_SIZE, "battery voltage: %d.%02d V", (int)voltage, (int)(voltage*100)%100);
+      client.publish("batteries/level", msg);
+      delay(500);
+  }
+  }
+  
+}
+
+void read_voltage(){
+  adcValue = analogRead(analogPin); /* Read the Analog Input value */
+  voltage = adcValue*conversion_factor;
+}
+
+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(), mqtt_user, mqtt_password)) {
+      Serial.println("connected");
+      // Once connected, publish an announcement...
+      client.publish("batteries/level", "ready");
+      // ... and resubscribe
+      client.subscribe("batteries/commands");
+    } 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_BUILTIN, OUTPUT);     // Initialize the BUILTIN_LED pin as an output
+  Serial.begin(115200);
+  setup_wifi();
+  client.setServer(mqtt_server, 1883);
+  client.setCallback(callback);
+  if( use_mcp == 1 ){
+    setup_mcp();
+  }
+  else {
+    setup_no_mcp();
+  }
+  
+}
+
+void loop() {
+
+  if (!client.connected()) {
+    reconnect();
+  }
+  client.loop();
+  
+  unsigned long now = millis();
+  
+  if(now - lastBatteryCheck > battery_check_interval){
+    lastBatteryCheck = now;
+    read_voltage();
+
+    if(voltage < min_voltage){
+      // Send the command to the MQTT broker to shutdown the Raspberry
+      Serial.println("Sending signal to shut down the PI");
+    }
+    
+  }
+
+
+  // Ajouter if(power_saving_mode == 1){ sleep(XXX); }
+
+  
+}