Heartbeat & Keep-Alive

VWire tracks device health using a combination of MQTT keep-alive (automatic) and optional application-level heartbeats (recommended for long-idle devices).

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MQTT keep-alive (automatic)

When the VWire library connects, it negotiates a 60-second keep-alive with the broker:

Event	What happens
Device publishes data	Keep-alive timer resets
No activity for 30 s	Library sends MQTT PINGREQ
Broker doesn't respond	Library considers connection lost
PING acknowledged	Timer resets, connection healthy
Connection truly dropped	Broker publishes LWT (status: offline)

This is all handled automatically — you don't need to write any PING code.

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Reconnect behavior

The VWire library reconnects automatically after a disconnect:

Disconnect → Wait 5 s → Reconnect attempt
           → Failed   → Wait 10 s → Retry
           → Failed   → Wait 30 s → Retry
           → ...exponential backoff, cap 120 s

After reconnecting, the library calls Vwire.syncVirtual() for all pins that were registered for sync.

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Application-level heartbeat (recommended)

For devices that sleep or have long idle periods, supplement MQTT keep-alive with a periodic data push:

unsigned long lastHeartbeat = 0;
const unsigned long HEARTBEAT_INTERVAL = 30000;  // 30 s

void loop() {
  Vwire.run();

  // Normal sensor data (infrequent)
  if (someCondition) {
    Vwire.virtualSend(V0, sensorValue);
  }

  // Heartbeat — just push uptime so the server sees activity
  if (millis() - lastHeartbeat >= HEARTBEAT_INTERVAL) {
    lastHeartbeat = millis();
    Vwire.virtualSend(V9, millis() / 1000);  // uptime in seconds
  }
}

Bind V9 to a Value Display widget labeled "Uptime (s)" to confirm the device is alive.

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Detecting device health in the dashboard

Indicator	Meaning
Green dot (Online)	MQTT connection active
Red dot (Offline)	MQTT LWT received or connection timed out
"Last Seen" timestamp	When the device last published any data

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Watchdog timer (ESP32 / ESP8266)

Enable the hardware watchdog as a safety net against firmware hangs:

#include <esp_task_wdt.h>

void setup() {
  esp_task_wdt_init(30, true);  // 30 s timeout, panic on hang
  esp_task_wdt_add(NULL);       // watch current task (loop)
  // ...
}

void loop() {
  Vwire.run();
  esp_task_wdt_reset();  // reset watchdog every loop
  // ...
}

If loop() ever stops running (stuck, blocked I/O), the watchdog resets the device and VWire reconnects automatically.