add ondemandwebportal example

examples/OnDemandWebPortal/OnDemandWebPortal.ino

@@ -0,0 +1,57 @@
+/**
+ * OnDemandWebPortal.ino
+ * example of running the webportal manually, independantly from the captiveportal
+ * trigger pin will start a webportal for 120 seconds then turn it off.
+ * 
+ */
+
+#include <ESP8266WiFi.h>          //https://github.com/esp8266/Arduino
+
+//needed for library
+#include <ESP8266WebServer.h>
+#include <DNSServer.h>
+#include <WiFiManager.h>          //https://github.com/tzapu/WiFiManager
+
+// select which pin will trigger the configuration portal when set to LOW
+// ESP-01 users please note: the only pins available (0 and 2), are shared 
+// with the bootloader, so always set them HIGH at power-up
+#define TRIGGER_PIN 0
+
+// set your ap credentials
+const char *ssid     = "********";
+const char *password = "********";
+
+int timeout          = 120; // seconds
+
+WiFiManager wifiManager;
+
+bool webportalrunning = false;
+int start             = millis();
+
+void setup() {
+  // put your setup code here, to run once:
+  Serial.begin(115200);
+  Serial.println("\n Starting");
+  pinMode(TRIGGER_PIN, INPUT_PULLUP);
+}
+
+
+void loop() {
+  
+  if(webportalrunning){
+    wifiManager.process();
+    if(millis()-start > timeout*1000){
+      Serial.println("webportaltimeout");
+      webportalrunning = false;
+      wifiManager.stopWebPortal(); // auto off
+   }
+  }
+
+  // is configuration portal requested?
+  if ( digitalRead(TRIGGER_PIN) == LOW && !webportalrunning) {
+    wifiManager.startWebPortal();
+    webportalrunning = true;
+    start = millis();
+  }
+  // put your main code here, to run repeatedly:
+}