kitchen_pilot_wire_control.ino: add an hearbeat led

soft/kitchen/kitchen_pilot_wire_control/kitchen_pilot_wire_control.ino

@@ -16,6 +16,11 @@ EspMQTTClient client(
 );
 
 const int heating_pin = 14;
+const int led_pin = 2;
+
+#define led_on(state) do {\
+  digitalWrite(led_pin, (state) ? LOW : HIGH); \
+} while (0)
 
 #define heater_on(pin) do {\
   digitalWrite(pin, LOW); \
@@ -58,6 +63,7 @@ void shutdown_heater(void *dummy)
 void setup()
 {
   pinMode(heating_pin, OUTPUT);
+  pinMode(led_pin, OUTPUT);
   heater_off(heating_pin);
 
   Serial.begin(115200);
@@ -80,9 +86,19 @@ void onConnectionEstablished()
 
 void loop()
 {
+  static unsigned int counter;
+  static bool led_state = false;
+
   client.loop();
   if (!client.isConnected()) {
     // if something wrong happens, switch off the heater
     heater_off(heating_pin);
   }
+
+  // blink ESP blue led to show that we are alive
+  if (((led_state) && (counter % 1000 == 0)) || (!led_state && (counter % 30000 == 0))) {
+    led_state = !led_state;
+    led_on(led_state);
+  }
+  counter++;
 }