diff --git a/src/DirectoryNode.cpp b/src/DirectoryNode.cpp
index c00d6e5..6af7cd6 100644
--- a/src/DirectoryNode.cpp
+++ b/src/DirectoryNode.cpp
@@ -102,7 +102,7 @@ void DirectoryNode::buildDirectoryTree(const char *currentPath)
             subdirectories.push_back(newNode);
             newNode->buildDirectoryTree((String(currentPath) + entry.name()).c_str());
         }
-        else if (String(entry.name()).endsWith(".mp3"))
+        else if (String(entry.name()).endsWith(".mp3")||String(entry.name()).endsWith(".MP3"))
         {
             mp3Files.push_back(entry.name());
             ids.push_back(getNextId());
diff --git a/src/WebContent.h b/src/WebContent.h
index bbf8908..e96a378 100644
--- a/src/WebContent.h
+++ b/src/WebContent.h
@@ -12,6 +12,7 @@ const char index_html[] PROGMEM = R"rawliteral(
     <span id="state"></span><br/><br/>
     <span id="voltage"></span><br/>
     <span id="uid"></span><br/>
+    <span id="heap"></span><br/>
 
 <div>
     <button class="prev-button" onclick="simpleGetCall('previous');""></button>
@@ -128,6 +129,7 @@ const char index_html[] PROGMEM = R"rawliteral(
     document.getElementById("state").innerHTML = state['title'];
     document.getElementById("progressLabel").innerHTML = state['time'];
     document.getElementById("voltage").innerHTML = state['voltage']+' mV';
+    document.getElementById("heap").innerHTML = state['heap']+' bytes free heap';
     document.getElementById("uid").innerHTML = 'Last NFC ID: '+state['uid'];
     var elements = document.getElementsByClassName('play-button');
     var btn = elements[0];
diff --git a/src/globals.h b/src/globals.h
index febda89..91c78ea 100644
--- a/src/globals.h
+++ b/src/globals.h
@@ -69,8 +69,6 @@ uint32_t lastVoltage = 0;
 
 uint loopCounter = 0;
 
-const int startDelay = 250;
-
 String lastUid = "";
 
 uint16_t currentSongId = 0;
diff --git a/src/main.cpp b/src/main.cpp
index 3e360e2..15c9fed 100644
--- a/src/main.cpp
+++ b/src/main.cpp
@@ -37,7 +37,13 @@
 
 #define VOLTAGE_LOOP_INTERVAL 5000
 
-#define VOLTAGE_THRESHOLD 3800
+#define VOLTAGE_THRESHOLD 0
+
+#define SHORT_PRESS_TIME 250
+
+#define LONG_PRESS_TIME 1000
+
+#define MAX_VOL 15
 
 #include "globals.h"
 #include "WebContent.h"
@@ -86,6 +92,8 @@ bool asyncPrev = false;
 
 uint16_t voltage_threshold_counter = 0;
 
+size_t free_heap = 0;
+
 /*
 std::map<String, String> rfid_map{{"67 152 204 14", "01-The_Box_Tops-The_Letter.mp3"},
                                   {"67 175 148 160", "068-Der_Schatz_im_Bergsee"}};
@@ -297,6 +305,7 @@ String getState()
   jsonState["length"] = audio.getAudioFileDuration();
   jsonState["voltage"] = lastVoltage;
   jsonState["uid"] = lastUid;
+  jsonState["heap"] = free_heap;
   String output;
   serializeJson(jsonState, output);
   jsonState.clear();
@@ -519,6 +528,8 @@ void setup()
 
   lastVoltage = getBatteryVoltageMv();
 
+  free_heap = xPortGetFreeHeapSize();
+
     // first parameter is name of access point, second is the password
   AsyncWiFiManager wifiManager(&server, &dns);
 
@@ -652,6 +663,11 @@ void volume_action(AsyncWebServerRequest *request)
   request->send_P(200, "text/plain", "ok");
 }
 
+String getStartupSoundDir() {
+  static String tempPath = "/"+sys_dir+"/"+startup_sound;
+  return tempPath;
+}
+
 void loop()
 {
   if (audio.isRunning())
@@ -681,8 +697,7 @@ void loop()
     playSongById(currentSongId,currentSongSeconds);    
   } else if (!startupSoundPlayed) {
     startupSoundPlayed = true;
-    String tempPath = "/"+sys_dir+"/"+startup_sound;
-    playSongByPath(tempPath.c_str());
+    playSongByPath(getStartupSoundDir().c_str());
   }
 
 
@@ -719,13 +734,33 @@ void loop()
   else if (asyncNext)
   {
     asyncNext = false;
-    next();
+    if (audio.isRunning()) {
+      next();
+    } else {
+      uint8_t vol = audio.getVolume();
+      if (vol!=MAX_VOL) {
+        vol++;
+      }
+      audio.setVolume(vol);
+      playSongByPath(getStartupSoundDir().c_str());
+
+    }
+    
   }
   else if (asyncPrev)
   {
     asyncPrev = false;
-    Serial.println("Previous");
-    previous();
+    if (audio.isRunning()) {
+      previous();
+    } else {
+      uint8_t vol = audio.getVolume();
+      if (vol!=0) {
+        vol--;
+      }
+      audio.setVolume(vol);
+      playSongByPath(getStartupSoundDir().c_str());
+    }
+    
   }
 
 
@@ -744,6 +779,7 @@ void loop()
   if (loopCounter % VOLTAGE_LOOP_INTERVAL == 0)
   {
     lastVoltage = getBatteryVoltageMv();
+    free_heap = xPortGetFreeHeapSize();
     if (lastVoltage<VOLTAGE_THRESHOLD) {
       if (voltage_threshold_counter>3) {
         Serial.println("entering deep sleep due to low voltage...");
@@ -766,10 +802,7 @@ void loop2(void *parameter)
   Serial.println("loop2 started");
   for (;;)
   {
-    if (buttonPressed(BTN_START_STOP))
-    {
-      asyncTogglePlayPause = true;
-    }
+    
     if (buttonPressed(BTN_NEXT))
     {
       asyncNext = true;
@@ -778,6 +811,10 @@ void loop2(void *parameter)
     {
       asyncPrev = true;
     }
+    if (buttonPressed(BTN_START_STOP))
+    {
+      asyncTogglePlayPause = true;
+    }
   }
 }
 
@@ -788,7 +825,7 @@ boolean buttonPressed(const uint8_t pin)
   {
 
     unsigned long now = millis();
-    if (now - lastStart > startDelay)
+    if (now - lastStart > SHORT_PRESS_TIME)
     {
       lastStart = now;
       Serial.println("button pressed.");
@@ -802,3 +839,4 @@ boolean buttonPressed(const uint8_t pin)
   
   return false;
 }
+