Add working version

platformio.ini

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+; PlatformIO Project Configuration File
+;
+;   Build options: build flags, source filter
+;   Upload options: custom upload port, speed and extra flags
+;   Library options: dependencies, extra library storages
+;   Advanced options: extra scripting
+;
+; Please visit documentation for the other options and examples
+; https://docs.platformio.org/page/projectconf.html
+
+
+[env:d1_mini]
+platform = espressif8266
+board = d1_mini
+framework = arduino
+monitor_speed = 115200
+
+[env]
+lib_deps = https://github.com/arduino-libraries/NTPClient
+           https://github.com/knolleary/pubsubclient

src/main.cpp

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+#include <Arduino.h>
+#include <ESP8266WiFi.h>
+#include <WiFiClient.h>
+#include <PubSubClient.h>
+#include <NTPClient.h>
+#include <WiFiUdp.h>
+
+#define MQTT_SERVER "mqtt.lan"
+#define MQTT_PORT 1883
+#define MQTT_PUB_TOPIC_DISTANCE "luftentfeuchter/distance-to-water"
+#define MQTT_PUB_TOPIC_DATE "luftentfeuchter/date"
+
+#define WIFI_SSID "XXX"
+#define WIFI_PASSWORD "XXX"
+
+WiFiClient espClient;
+PubSubClient client(espClient);
+
+WiFiUDP ntpUDP;
+NTPClient timeClient(ntpUDP);
+
+long lastMsg = 0;
+char data[75];
+
+void setup() {
+  // Status LED (onboard)
+  pinMode(LED_BUILTIN, OUTPUT);
+
+  // MoistureSensor
+  pinMode(D6, INPUT);
+
+  // HallSensor
+  pinMode(D7, INPUT); // Echo
+  pinMode(D8, OUTPUT); // Trigger
+
+  // Relay
+  pinMode(D2, OUTPUT);
+  
+  digitalWrite(LED_BUILTIN, LOW);
+
+  WiFi.setAutoConnect(true);
+  WiFi.setAutoReconnect(true);
+  WiFi.hostname("luftentfeuchter-pumpe");
+
+  WiFi.begin(WIFI_SSID, WIFI_PASSWORD);
+  while (WiFi.status() != WL_CONNECTED) {
+      delay(2000);
+  }
+  client.setServer(MQTT_SERVER, MQTT_PORT);
+
+  timeClient.begin();
+
+  digitalWrite(LED_BUILTIN, HIGH);
+}
+
+int connectToMQTT() {
+  if (client.connected()) {
+    return 0;
+  }
+
+  String clientId = "luftentfeuchter-pumpe";
+  if (client.connect(clientId.c_str())) {
+    return 0;
+  }
+
+  return 1;
+}
+
+int measureDistanceToWater() {
+  digitalWrite(D8, LOW);
+  delayMicroseconds(2);
+  digitalWrite(D8, HIGH);
+  delayMicroseconds(10);
+  digitalWrite(D8, LOW);
+
+  long duration = pulseIn(D7, HIGH);
+  int distance = duration * 0.034 / 2;
+
+  return distance;
+}
+
+bool isMoistureSensorSubmerged() {
+  return digitalRead(D6) == HIGH;
+}
+
+void loop() {
+  if (!WiFi.isConnected()) {
+    WiFi.reconnect();
+  }
+  connectToMQTT();
+  timeClient.update();
+
+  int distance = measureDistanceToWater();
+  snprintf(data, sizeof(data), "%d", distance);
+  client.publish(MQTT_PUB_TOPIC_DISTANCE, data);
+
+  snprintf(data, sizeof(data), "%d", timeClient.getEpochTime());
+  client.publish(MQTT_PUB_TOPIC_DATE, data);
+
+  if (distance <= 13) {
+    // Turn on the status LED
+    digitalWrite(LED_BUILTIN, LOW);
+
+    // Run the pump for 2 minutes, 45 seconds
+    digitalWrite(D2, HIGH);
+    delay((60+60+45) * 1000);
+    digitalWrite(D2, LOW);
+
+    // Turn the status LED off again
+    digitalWrite(LED_BUILTIN, HIGH);
+  } else {
+    digitalWrite(LED_BUILTIN, HIGH);
+    digitalWrite(D2, LOW);
+  }
+
+  // Wait for a minute
+  delay(60000);
+}