diff --git a/README.md b/README.md
index 0fa85e7a..500457b2 100644
--- a/README.md
+++ b/README.md
@@ -156,10 +156,10 @@ Note: all settings are stored in NVRAM and will be reloaded when device starts.
 	1 = reset MAC counter to zero
 	2 = reset device to factory settings
 
-0x0A set Wifi scan cycle and payload transmit cycle
+0x0A set payload send cycle
 
-	0 ... 255 duration of a wifi scan cycle in seconds/2, after this payload is sent
-	e.g. 120 -> 1 cycle runs for 240 seconds [default]
+	0 ... 255 payload send cycle in seconds/2
+	e.g. 120 -> payload is transmitted each 240 seconds [default]
 
 0x0B set Wifi channel switch interval timer
 
@@ -193,7 +193,7 @@ Note: all settings are stored in NVRAM and will be reloaded when device starts.
 
 0x80 get device configuration
 
-device answers with it's current configuration. The configuration is a C structure declared in file [globals.h](src/globals.h#L24-L41) with the following definition:
+device answers with it's current configuration. The configuration is a C structure declared in file [globals.h](src/globals.h#L27-L44) with the following definition:
 
 	byte 1:			Lora SF (7..12)
 	byte 2:			Lora TXpower (2..15)
@@ -202,7 +202,7 @@ device answers with it's current configuration. The configuration is a C structu
 	byte 5:			Display status (1=on, 0=off)
 	byte 6:			Counter mode (0=cyclic unconfirmed, 1=cumulative, 2=cyclic confirmed)
 	bytes 7-8:		RSSI limiter threshold value (negative)
-	byte 9:			Wifi scan cycle duration in seconds/2 (0..255)
+	byte 9:			Payload send cycle in seconds/2 (0..255)
 	byte 10:		Wifi channel switch interval in seconds/100 (0..255)
 	byte 11:		BLE scan cycle duration in seconds (0..255)
 	byte 12:		BLE scan mode (1=on, 0=0ff)
diff --git a/src/antenna.cpp b/src/antenna.cpp
index 8bf94a2c..bcbf1703 100644
--- a/src/antenna.cpp
+++ b/src/antenna.cpp
@@ -21,7 +21,7 @@ void antenna_init(void) {
         gpio_config(&gpioconf);
 }
 
-void antenna_select (const int8_t _ant) {
+void antenna_select (const uint8_t _ant) {
         if (HAS_ANTENNA_SWITCH < 32) {
             if (_ant == ANTENNA_EXT) {
                 GPIO_REG_WRITE(GPIO_OUT_W1TS_REG, 1 << HAS_ANTENNA_SWITCH);
diff --git a/src/blecsan.cpp b/src/blecsan.cpp
index 8dd4bb15..4c2bb9af 100644
--- a/src/blecsan.cpp
+++ b/src/blecsan.cpp
@@ -100,7 +100,7 @@ static void gap_callback_handler(esp_gap_ble_cb_event_t event, esp_ble_gap_cb_pa
 	{
 		case ESP_GAP_BLE_SCAN_PARAM_SET_COMPLETE_EVT:
 		{	// restart scan
-			status = esp_ble_gap_start_scanning(BLESCANTIME); 
+			status = esp_ble_gap_start_scanning(cfg.blescantime); 
 			if (status != ESP_OK) 
 			{
 				ESP_LOGE(TAG, "esp_ble_gap_start_scanning: rc=%d", status);
@@ -112,7 +112,7 @@ static void gap_callback_handler(esp_gap_ble_cb_event_t event, esp_ble_gap_cb_pa
 		{		
 			if ( p->scan_rst.search_evt == ESP_GAP_SEARCH_INQ_CMPL_EVT) // Inquiry complete, scan is done
 			{	// restart scan
-				status = esp_ble_gap_start_scanning	(BLESCANTIME); 
+				status = esp_ble_gap_start_scanning	(cfg.blescantime); 
 				if (status != ESP_OK) 
 				{
 					ESP_LOGE(TAG, "esp_ble_gap_start_scanning: rc=%d", status);
@@ -286,8 +286,7 @@ void bt_loop(void * pvParameters)
 
 	while(1)
     {
-		vTaskDelay(10/portTICK_PERIOD_MS);
-        yield();
+		vTaskDelay(10/portTICK_PERIOD_MS); // reset watchdog
     }
 
 end:
diff --git a/src/configmanager.cpp b/src/configmanager.cpp
index 628e4cd3..74c26206 100644
--- a/src/configmanager.cpp
+++ b/src/configmanager.cpp
@@ -13,7 +13,7 @@ esp_err_t err;
 
 // defined in antenna.cpp
 #ifdef HAS_ANTENNA_SWITCH
-    void antenna_select(const int8_t _ant);
+    void antenna_select(const uint8_t _ant);
 #endif
 
 // populate cfg vars with factory settings
@@ -25,7 +25,7 @@ void defaultConfig() {
     cfg.screenon      = 1;              // 0=disbaled, 1=enabled
     cfg.countermode   = 0;              // 0=cyclic, 1=cumulative, 2=cyclic confirmed
     cfg.rssilimit     = 0;              // threshold for rssilimiter, negative value!
-    cfg.wifiscancycle = SEND_SECS;      // wifi scan cycle [seconds/2]
+    cfg.sendcycle     = SEND_SECS;      // payload send cycle [seconds/2]
     cfg.wifichancycle = WIFI_CHANNEL_SWITCH_INTERVAL; // wifi channel switch cycle [seconds/100]
     cfg.blescantime   = BLESCANTIME;    // BLE scan cycle duration [seconds]
     cfg.blescan       = 1;              // 0=disabled, 1=enabled
@@ -99,8 +99,8 @@ void saveConfig() {
       if( nvs_get_i8(my_handle, "countermode", &flash8) != ESP_OK || flash8 != cfg.countermode )
         nvs_set_i8(my_handle, "countermode", cfg.countermode);
 
-      if( nvs_get_i8(my_handle, "wifiscancycle", &flash8) != ESP_OK || flash8 != cfg.wifiscancycle )
-        nvs_set_i8(my_handle, "wifiscancycle", cfg.wifiscancycle);
+      if( nvs_get_i8(my_handle, "sendcycle", &flash8) != ESP_OK || flash8 != cfg.sendcycle )
+        nvs_set_i8(my_handle, "sendcycle", cfg.sendcycle);
 
       if( nvs_get_i8(my_handle, "wifichancycle", &flash8) != ESP_OK || flash8 != cfg.wifichancycle )
         nvs_set_i8(my_handle, "wifichancycle", cfg.wifichancycle);
@@ -220,11 +220,11 @@ void loadConfig() {
       saveConfig();
     }
 
-    if( nvs_get_i8(my_handle, "wifiscancycle", &flash8) == ESP_OK ) {
-      cfg.wifiscancycle = flash8;
-      ESP_LOGI(TAG, "wifiscancycle = %d", flash8);
+    if( nvs_get_i8(my_handle, "sendcycle", &flash8) == ESP_OK ) {
+      cfg.sendcycle = flash8;
+      ESP_LOGI(TAG, "sendcycle = %d", flash8);
     } else {
-      ESP_LOGI(TAG, "WIFI scan cycle set to default %d", cfg.wifiscancycle);
+      ESP_LOGI(TAG, "Payload send cycle set to default %d", cfg.sendcycle);
       saveConfig();
     }
 
diff --git a/src/globals.h b/src/globals.h
index 7035c7d2..2578596d 100644
--- a/src/globals.h
+++ b/src/globals.h
@@ -26,33 +26,33 @@
 
 // Struct holding devices's runtime configuration
 typedef struct {
-  int8_t lorasf;                       // 7-12, lora spreadfactor
-  int8_t txpower;                      // 2-15, lora tx power
-  int8_t adrmode;                      // 0=disabled, 1=enabled
-  int8_t screensaver;                  // 0=disabled, 1=enabled
-  int8_t screenon;                     // 0=disabled, 1=enabled
-  int8_t countermode;                  // 0=cyclic unconfirmed, 1=cumulative, 2=cyclic confirmed
+  uint8_t lorasf;                       // 7-12, lora spreadfactor
+  uint8_t txpower;                      // 2-15, lora tx power
+  uint8_t adrmode;                      // 0=disabled, 1=enabled
+  uint8_t screensaver;                  // 0=disabled, 1=enabled
+  uint8_t screenon;                     // 0=disabled, 1=enabled
+  uint8_t countermode;                  // 0=cyclic unconfirmed, 1=cumulative, 2=cyclic confirmed
   int16_t rssilimit;                   // threshold for rssilimiter, negative value!
-  int8_t wifiscancycle;                // wifi scan cycle [seconds/2]
-  int8_t wifichancycle;                // wifi channel switch cycle [seconds/100]
-  int8_t blescantime;                  // BLE scan cycle duration [seconds]
-  int8_t blescan;                      // 0=disabled, 1=enabled
-  int8_t wifiant;                      // 0=internal, 1=external (for LoPy/LoPy4)
-  int8_t vendorfilter;                 // 0=disabled, 1=enabled
-  int8_t rgblum;                       // RGB Led luminosity (0..100%)
+  uint8_t sendcycle;                    // payload send cycle [seconds/2]
+  uint8_t wifichancycle;                // wifi channel switch cycle [seconds/100]
+  uint8_t blescantime;                  // BLE scan cycle duration [seconds]
+  uint8_t blescan;                      // 0=disabled, 1=enabled
+  uint8_t wifiant;                      // 0=internal, 1=external (for LoPy/LoPy4)
+  uint8_t vendorfilter;                 // 0=disabled, 1=enabled
+  uint8_t rgblum;                       // RGB Led luminosity (0..100%)
   char version[10];                    // Firmware version
   } configData_t;
 
 extern configData_t cfg;
 extern uint8_t mydata[];
 extern uint64_t uptimecounter;
-extern unsigned long currentMillis ;
 extern osjob_t sendjob;
 extern char display_lora[], display_lmic[];
 extern int countermode, screensaver, adrmode, lorasf, txpower, rlim;
 extern uint16_t macs_total, macs_wifi, macs_ble; // MAC counters
 extern bool joinstate;
-extern std::set<uint16_t> macs; 
+extern std::set<uint16_t> macs;
+extern hw_timer_t * channelSwitch;      // hardware timer used for wifi channel switching
 
 #ifdef HAS_DISPLAY
     extern HAS_DISPLAY u8x8;
diff --git a/src/hal/heltec.h b/src/hal/heltec.h
index eb9aa31c..ed2e63db 100644
--- a/src/hal/heltec.h
+++ b/src/hal/heltec.h
@@ -17,7 +17,7 @@
 #define RST   14 // ESP32 GPIO14 (Pin14) -- SX1276 NRESET (Pin7) Reset Trigger Input
 #define DIO0  26 // ESP32 GPIO26 (Pin15) -- SX1276 DIO0 (Pin8) used by LMIC for detecting LoRa RX_Done & TX_Done
 #define DIO1  33 // ESP32 GPIO33 (Pin13) -- SX1276 DIO1 (Pin9) used by LMIC for detecting LoRa RX_Timeout
-#define DIO2  32 // ESP32 GPIO32 (Pin12) -- SX1276 DIO2 (Pin10) not used by LMIC for LoRa (Timeout for FSK only)
+#define DIO2  LMIC_UNUSED_PIN // 32 ESP32 GPIO32 (Pin12) -- SX1276 DIO2 (Pin10) not used by LMIC for LoRa (Timeout for FSK only)
 
 // Hardware pin definitions for Heltec LoRa-32 Board with OLED SSD1306 I2C Display
 #define OLED_RST 16 // ESP32 GPIO16 (Pin16) -- SD1306 RST
diff --git a/src/hal/lolin32_lora.h b/src/hal/lolin32_lora.h
index a1bdbe09..ca5929af 100644
--- a/src/hal/lolin32_lora.h
+++ b/src/hal/lolin32_lora.h
@@ -25,8 +25,8 @@
 #define RST   25 // ESP32 GPIO25 (Pin25) -- SX1276 NRESET (Pin7)  Reset Trigger Input
 #define DIO0  27 // ESP32 GPIO27 (Pin27) -- SX1276 DIO0   (Pin8)  used by LMIC for detecting LoRa RX_Done & TX_Done
 #define DIO1  26 // ESP32 GPIO26 (Pin26) -- SX1276 DIO1   (Pin9)  used by LMIC for detecting LoRa RX_Timeout
-#define DIO2   4 // ESP32  GPIO4 (Pin4)  -- SX1276 DIO2   (Pin10) not used by LMIC for LoRa (Timeout for FSK only)
-#define DIO5  35 // ESP32 GPIO35 (Pin35) -- SX1276 DIO5   not used by LMIC for LoRa (Timeout for FSK only)
+#define DIO2  LMIC_UNUSED_PIN // 4 ESP32  GPIO4 (Pin4)  -- SX1276 DIO2   (Pin10) not used by LMIC for LoRa (Timeout for FSK only)
+#define DIO5  LMIC_UNUSED_PIN // 35 ESP32 GPIO35 (Pin35) -- SX1276 DIO5   not used by LMIC for LoRa (Timeout for FSK only)
 
 // Hardware pin definitions for LoRaNode32 Board with OLED I2C Display
 #define OLED_RST U8X8_PIN_NONE  // Not reset pin
diff --git a/src/hal/lolin32lite_lora.h b/src/hal/lolin32lite_lora.h
index fe2adac8..51cd6f10 100644
--- a/src/hal/lolin32lite_lora.h
+++ b/src/hal/lolin32lite_lora.h
@@ -24,8 +24,8 @@
 #define RST   25 // ESP32 GPIO25 (Pin25) -- SX1276 NRESET (Pin7)  Reset Trigger Input
 #define DIO0  27 // ESP32 GPIO27 (Pin27) -- SX1276 DIO0   (Pin8)  used by LMIC for detecting LoRa RX_Done & TX_Done
 #define DIO1  26 // ESP32 GPIO26 (Pin26) -- SX1276 DIO1   (Pin9)  used by LMIC for detecting LoRa RX_Timeout
-#define DIO2   4 // ESP32  GPIO4 (Pin4)  -- SX1276 DIO2   (Pin10) not used by LMIC for LoRa (Timeout for FSK only)
-#define DIO5  35 // ESP32 GPIO35 (Pin35) -- SX1276 DIO5   not used by LMIC for LoRa (Timeout for FSK only)
+#define DIO2  LMIC_UNUSED_PIN // 4 ESP32  GPIO4 (Pin4)  -- SX1276 DIO2   (Pin10) not used by LMIC for LoRa (Timeout for FSK only)
+#define DIO5  LMIC_UNUSED_PIN // 35 ESP32 GPIO35 (Pin35) -- SX1276 DIO5   not used by LMIC for LoRa (Timeout for FSK only)
 
 // Hardware pin definitions for LoRaNode32 Board with OLED I2C Display
 #define OLED_RST U8X8_PIN_NONE  // Not reset pin
diff --git a/src/hal/lopy.h b/src/hal/lopy.h
index fffb2294..3e34dc8f 100644
--- a/src/hal/lopy.h
+++ b/src/hal/lopy.h
@@ -12,7 +12,7 @@
 #define RST   18
 #define DIO0  23 // LoRa IRQ
 #define DIO1  23 // workaround
-#define DIO2  23 // workaround
+#define DIO2  LMIC_UNUSED_PIN // 23 workaround
 
 // select WIFI antenna (internal = onboard / external = u.fl socket)
 #define HAS_ANTENNA_SWITCH  16      // pin for switching wifi antenna
diff --git a/src/hal/lopy4.h b/src/hal/lopy4.h
index 4ff9ac72..223e26b5 100644
--- a/src/hal/lopy4.h
+++ b/src/hal/lopy4.h
@@ -12,7 +12,7 @@
 #define RST   LMIC_UNUSED_PIN
 #define DIO0  23 // LoRa IRQ
 #define DIO1  23 // workaround
-#define DIO2  23 // workaround 
+#define DIO2  LMIC_UNUSED_PIN // 23 workaround 
 
 // select WIFI antenna (internal = onboard / external = u.fl socket)
 #define HAS_ANTENNA_SWITCH  21      // pin for switching wifi antenna
diff --git a/src/hal/ttgov1.h b/src/hal/ttgov1.h
index ab6b4f2c..c8e1a12d 100644
--- a/src/hal/ttgov1.h
+++ b/src/hal/ttgov1.h
@@ -18,7 +18,7 @@
 #define RST   14 // ESP32 GPIO14 (Pin14) -- SX1276 NRESET (Pin7) Reset Trigger Input
 #define DIO0  26 // ESP32 GPIO26 (Pin15) -- SX1276 DIO0 (Pin8) used by LMIC for detecting LoRa RX_Done & TX_Done
 #define DIO1  33 // ESP32 GPIO33 (Pin13) -- SX1276 DIO1 (Pin9) used by LMIC for detecting LoRa RX_Timeout
-#define DIO2  32 // ESP32 GPIO32 (Pin12) -- SX1276 DIO2 (Pin10) not used by LMIC for LoRa (Timeout for FSK only)
+#define DIO2  LMIC_UNUSED_PIN // 32 ESP32 GPIO32 (Pin12) -- SX1276 DIO2 (Pin10) not used by LMIC for LoRa (Timeout for FSK only)
 
 // Hardware pin definitions for TTGOv1 Board with OLED SSD1306 I2C Display
 #define OLED_RST 16 // ESP32 GPIO16 (Pin16) -- SD1306 Reset
diff --git a/src/hal/ttgov2.h b/src/hal/ttgov2.h
index 537990af..ebdfe87d 100644
--- a/src/hal/ttgov2.h
+++ b/src/hal/ttgov2.h
@@ -19,7 +19,7 @@
 #define RST   LMIC_UNUSED_PIN // connected to ESP32 RST/EN
 #define DIO0  26 // ESP32 GPIO26 wired on PCB to HPD13A
 #define DIO1  33 // HPDIO1 on pcb, needs to be wired external to GPIO33
-#define DIO2  32 // HPDIO2 on pcb, needs to be wired external to GPIO32 (not necessary for LoRa, only FSK)
+#define DIO2  LMIC_UNUSED_PIN // 32 HPDIO2 on pcb, needs to be wired external to GPIO32 (not necessary for LoRa, only FSK)
 
 // Hardware pin definitions for TTGO V2 Board with OLED SSD1306 0,96" I2C Display
 #define OLED_RST U8X8_PIN_NONE // connected to CPU RST/EN
diff --git a/src/lorawan.cpp b/src/lorawan.cpp
index b4f09726..a5e3e90a 100644
--- a/src/lorawan.cpp
+++ b/src/lorawan.cpp
@@ -14,8 +14,8 @@
 static const char *TAG = "lorawan";
 
 // functions defined in rcommand.cpp
-void rcommand(int cmd, int arg);
-void switch_lora(int sf, int tx);
+void rcommand(uint8_t cmd, uint8_t arg);
+void switch_lora(uint8_t sf, uint8_t tx);
 
 // DevEUI generator using devices's MAC address
 void gen_lora_deveui(uint8_t *pdeveui) {
@@ -140,7 +140,7 @@ void do_send(osjob_t* j){
     }
 
     // Schedule next transmission
-    os_setTimedCallback(&sendjob, os_getTime()+sec2osticks(SEND_SECS * 2), do_send);
+    os_setTimedCallback(&sendjob, os_getTime()+sec2osticks(cfg.sendcycle * 2), do_send);
 
 } // do_send()
 
diff --git a/src/main.cpp b/src/main.cpp
index 8aff95ee..5f360faa 100644
--- a/src/main.cpp
+++ b/src/main.cpp
@@ -41,8 +41,6 @@ Refer to LICENSE.txt file in repository for more details.
 configData_t cfg;                   // struct holds current device configuration
 osjob_t sendjob, initjob;           // LMIC jobs
 uint64_t uptimecounter = 0;         // timer global for uptime counter
-unsigned long currentMillis = millis();  // timer global for state machine
-unsigned long previousDisplaymillis = currentMillis; // Display refresh for state machine
 uint8_t DisplayState = 0;           // globals for state machine
 uint16_t macs_total = 0, macs_wifi = 0, macs_ble = 0;   // MAC counters globals for display
 uint8_t channel = 0;                // wifi channel rotation counter global for display
@@ -54,11 +52,15 @@ uint16_t LEDBlinkDuration = 0;      // How long the blink need to be
 uint16_t LEDColor = COLOR_NONE;     // state machine variable to set RGB LED color
 bool joinstate = false;             // LoRa network joined? global flag
 bool blinkdone = true;              // flag for state machine for blinking LED once
+hw_timer_t * displaytimer = NULL;   // configure hardware timer used for cyclic display refresh
+hw_timer_t * channelSwitch = NULL;  // configure hardware timer used for wifi channel switching
+
+portMUX_TYPE timerMux = portMUX_INITIALIZER_UNLOCKED; // sync main loop and ISR when modifying shared variable DisplayIRQ
 
 std::set<uint16_t> macs; // associative container holds total of unique MAC adress hashes (Wifi + BLE)
 
-// this variable will be changed in the ISR, and read in main loop
-static volatile bool ButtonTriggered = false;
+// this variables will be changed in the ISR, and read in main loop
+static volatile int ButtonPressed = 0, DisplayTimerIRQ = 0, ChannelTimerIRQ = 0;
 
 // local Tag for logging
 static const char *TAG = "paxcnt";
@@ -165,11 +167,9 @@ void lorawan_loop(void * pvParameters) {
                 LMIC_reset(); // Reset the MAC state. Session and pending data transfers will be discarded.
             };
             vTaskDelay(1000/portTICK_PERIOD_MS);
-            yield();
         }
 */
-        vTaskDelay(10/portTICK_PERIOD_MS);
-        yield();
+        vTaskDelay(10/portTICK_PERIOD_MS); // reset watchdog
     }    
 }
 
@@ -181,12 +181,18 @@ void lorawan_loop(void * pvParameters) {
 
 #ifdef HAS_DISPLAY
     HAS_DISPLAY u8x8(OLED_RST, OLED_SCL, OLED_SDA);
+    // Display Refresh IRQ
+    void IRAM_ATTR DisplayIRQ() {
+        portENTER_CRITICAL_ISR(&timerMux);
+        DisplayTimerIRQ++;
+        portEXIT_CRITICAL_ISR(&timerMux);
+    }
 #endif
 
 #ifdef HAS_ANTENNA_SWITCH
     // defined in antenna.cpp
     void antenna_init();
-    void antenna_select(const int8_t _ant);
+    void antenna_select(const uint8_t _ant);
 #endif
 
 #ifndef BLECOUNTER
@@ -194,12 +200,19 @@ void lorawan_loop(void * pvParameters) {
 #endif
 
 #ifdef HAS_BUTTON
-    // Button Handling, board dependent -> perhaps to be moved to hal/<$board.h>
+    // Button IRQ
     // IRAM_ATTR necessary here, see https://github.com/espressif/arduino-esp32/issues/855
-    void IRAM_ATTR isr_button_pressed(void) {
-        ButtonTriggered = true; }
+    void IRAM_ATTR ButtonIRQ() {
+        ButtonPressed++;
+    }
 #endif
 
+void IRAM_ATTR ChannelSwitchIRQ() {
+    portENTER_CRITICAL(&timerMux);
+    ChannelTimerIRQ++;
+    portEXIT_CRITICAL(&timerMux);
+}
+
 /* end hardware specific parts -------------------------------------------------------- */
 
 
@@ -212,12 +225,16 @@ void sniffer_loop(void * pvParameters) {
 
   	while (1) {
 
-        for (channel = 1; channel <= WIFI_CHANNEL_MAX; channel++) {
-        // rotates variable channel 1..WIFI_CHANNEL_MAX
+        if (ChannelTimerIRQ) {
+            portENTER_CRITICAL(&timerMux);
+            ChannelTimerIRQ--;
+            portEXIT_CRITICAL(&timerMux);
+            // rotates variable channel 1..WIFI_CHANNEL_MAX
+            channel = (channel % WIFI_CHANNEL_MAX) + 1;
             wifi_sniffer_set_channel(channel);
             ESP_LOGD(TAG, "Wifi set channel %d", channel);
-            vTaskDelay(cfg.wifichancycle*10 / portTICK_PERIOD_MS);
-            yield();
+
+            vTaskDelay(10/portTICK_PERIOD_MS); // reset watchdog
         }
 
     } // end of infinite wifi channel rotation loop
@@ -313,16 +330,20 @@ uint64_t uptime() {
                 u8x8.printf("%-16s", "BLTH:off");
         #endif
 
-        // update free memory display (line 4)
-        u8x8.setCursor(10,4);
-        u8x8.printf("%4dKB", ESP.getFreeHeap() / 1024);
+        // update LoRa SF display (line 3)
+        u8x8.setCursor(11,3);
+        u8x8.printf("SF:%c%c", lora_datarate[LMIC.datarate * 2], lora_datarate[LMIC.datarate * 2 + 1]);
 
-        // update RSSI limiter status & wifi channel display (line 5)
-        u8x8.setCursor(0,5);
-        u8x8.printf(!cfg.rssilimit ? "RLIM:off " : "RLIM:%-4d", cfg.rssilimit);
-        u8x8.setCursor(11,5);
+        // update wifi channel display (line 4)
+        u8x8.setCursor(11,4);
         u8x8.printf("ch:%02d", channel);
 
+        // update RSSI limiter status & free memory display (line 5)
+        u8x8.setCursor(0,5);
+        u8x8.printf(!cfg.rssilimit ? "RLIM:off " : "RLIM:%-4d", cfg.rssilimit);
+        u8x8.setCursor(10,5);
+        u8x8.printf("%4dKB", ESP.getFreeHeap() / 1024);
+        
         // update LoRa status display (line 6)
         u8x8.setCursor(0,6);
         u8x8.printf("%-16s", display_lora);
@@ -333,26 +354,27 @@ uint64_t uptime() {
     }    
 
     void updateDisplay() {
-        // timed display refresh according to refresh cycle setting
-        
-        if (currentMillis - previousDisplaymillis >= DISPLAYREFRESH_MS) {
+        // refresh display according to refresh cycle setting
+        if (DisplayTimerIRQ) {
+            portENTER_CRITICAL(&timerMux);
+            DisplayTimerIRQ--;
+            portEXIT_CRITICAL(&timerMux);
+
             refreshDisplay();
-            previousDisplaymillis += DISPLAYREFRESH_MS;
-        }
-        // set display on/off according to current device configuration
-        if (DisplayState != cfg.screenon) {
-            DisplayState = cfg.screenon;
-            u8x8.setPowerSave(!cfg.screenon);
+        
+            // set display on/off according to current device configuration
+            if (DisplayState != cfg.screenon) {
+                DisplayState = cfg.screenon;
+                u8x8.setPowerSave(!cfg.screenon);
+            }
         }
     } // updateDisplay()
-
-
 #endif // HAS_DISPLAY
 
 #ifdef HAS_BUTTON
     void readButton() {
-        if (ButtonTriggered) {
-            ButtonTriggered = false;
+        if (ButtonPressed) {
+            ButtonPressed--;
             ESP_LOGI(TAG, "Button pressed, resetting device to factory defaults");
             eraseConfig();
             esp_restart();
@@ -497,12 +519,12 @@ void setup() {
         strcat(features, "PU");
         // install button interrupt (pullup mode)
         pinMode(HAS_BUTTON, INPUT_PULLUP);
-        attachInterrupt(digitalPinToInterrupt(HAS_BUTTON), isr_button_pressed, RISING); 
+        attachInterrupt(digitalPinToInterrupt(HAS_BUTTON), ButtonIRQ, RISING); 
     #else
         strcat(features, "PD");
         // install button interrupt (pulldown mode)
         pinMode(HAS_BUTTON, INPUT_PULLDOWN);
-        attachInterrupt(digitalPinToInterrupt(HAS_BUTTON), isr_button_pressed, FALLING); 
+        attachInterrupt(digitalPinToInterrupt(HAS_BUTTON), ButtonIRQ, FALLING); 
     #endif
 #endif
 
@@ -529,9 +551,21 @@ void setup() {
     u8x8.printf(!cfg.rssilimit ? "RLIM:off " : "RLIM:%d", cfg.rssilimit);
     
     sprintf(display_lora, "Join wait");
+
+    // setup Display IRQ, thanks to https://techtutorialsx.com/2017/10/07/esp32-arduino-timer-interrupts/
+    displaytimer = timerBegin(0, 80, true);                        // prescaler 80 -> divides 80 MHz CPU freq to 1 MHz, timer 0, count up
+    timerAttachInterrupt(displaytimer, &DisplayIRQ, true);         // interrupt handler DisplayIRQ, triggered by edge
+    timerAlarmWrite(displaytimer, DISPLAYREFRESH_MS * 1000, true); // reload interrupt after each trigger of display refresh cycle
+    timerAlarmEnable(displaytimer);                                // enable display interrupt
 #endif
 
-// Display features compiled for
+// setup channel rotation IRQ, thanks to https://techtutorialsx.com/2017/10/07/esp32-arduino-timer-interrupts/
+channelSwitch = timerBegin(1, 80, true);                        // prescaler 80 -> divides 80 MHz CPU freq to 1 MHz, timer 1, count up
+timerAttachInterrupt(channelSwitch, &ChannelSwitchIRQ, true);   // interrupt handler, triggered by edge
+timerAlarmWrite(channelSwitch, cfg.wifichancycle * 10000, true); // reload interrupt after each trigger of channel switch cycle
+timerAlarmEnable(channelSwitch);                                // enable channel switching interrupt
+
+// show compiled features
 ESP_LOGI(TAG, "Features %s", features);
 
 // output LoRaWAN keys to console
@@ -579,7 +613,6 @@ void loop() {
 
     // simple state machine for controlling display, LED, button, etc.
     uptimecounter = uptime() / 1000;    // counts uptime in seconds (64bit)
-    currentMillis = millis();           // timebase for state machine in milliseconds (32bit)
 
     #if (HAS_LED != NOT_A_PIN) || defined (HAS_RGB_LED)
         led_loop();
@@ -600,6 +633,8 @@ void loop() {
         reset_salt();       // get new salt for salting hashes
     }
 
+    vTaskDelay(10/portTICK_PERIOD_MS); // reset watchdog
+
  }
 
 /* end Aruino LOOP ------------------------------------------------------------ */
diff --git a/src/main.h b/src/main.h
index 8b0d5b60..5ad9b39b 100644
--- a/src/main.h
+++ b/src/main.h
@@ -1,6 +1,6 @@
 
 // program version - note: increment version after modifications to configData_t struct!!
-#define PROGVERSION                     "1.3.3"    // use max 10 chars here!
+#define PROGVERSION                     "1.3.4"    // use max 10 chars here!
 #define PROGNAME                        "PAXCNT"
 
 //--- Declarations ---
@@ -10,6 +10,12 @@ enum led_states {
   LED_ON
 };
 
+#if defined(CFG_eu868)
+  const char lora_datarate[] = {"1211100908077BFSNA"};
+#elif defined(CFG_us915)  
+  const char lora_datarate[] = {"100908078CNA121110090807"};
+#endif
+
 //--- Prototypes ---
 
 // defined in main.cpp
diff --git a/src/paxcounter.conf b/src/paxcounter.conf
index ec8c455a..cc953b6b 100644
--- a/src/paxcounter.conf
+++ b/src/paxcounter.conf
@@ -34,7 +34,7 @@
 
 // LoRa payload send cycle --> take care of duty cycle of LoRaWAN network! <--
 #define SEND_SECS                       120     // [seconds/2] -> 240 sec.
-#define MEM_LOW                         2048    // [Bytes] memory threshold triggering send cycle
+#define MEM_LOW                         2048    // [Bytes] low memory threshold triggering a send cycle
 
 // Default LoRa Spreadfactor
 #define LORASFDEFAULT                   9       // 7 ... 12 SF, according to LoRaWAN specs
@@ -45,7 +45,7 @@
 #define RGBLUMINOSITY                   30      // 30%
 
 // OLED Display refresh cycle (in Milliseconds)
-#define DISPLAYREFRESH_MS               40       // e.g. 40ms -> 1000/40 = 25 frames per second
+#define DISPLAYREFRESH_MS               40      // e.g. 40ms -> 1000/40 = 25 frames per second
 
 // LMIC settings
 // define hardware independent LMIC settings here, settings of standard library in /lmic/config.h will be ignored
diff --git a/src/rcommand.cpp b/src/rcommand.cpp
index 90894149..95ccee33 100644
--- a/src/rcommand.cpp
+++ b/src/rcommand.cpp
@@ -14,18 +14,18 @@ static const char *TAG = "rcommand";
 
 // table of remote commands and assigned functions
 typedef struct {
-    const int nam;
-    void (*func)(int);
+    const uint8_t nam;
+    void (*func)(uint8_t);
     const bool store;
 } cmd_t;
 
 // function defined in antenna.cpp
 #ifdef HAS_ANTENNA_SWITCH
-    void antenna_select(const int8_t _ant);
+    void antenna_select(const uint8_t _ant);
 #endif
 
 // help function to assign LoRa datarates to numeric spreadfactor values
-void switch_lora (int sf, int tx) {
+void switch_lora (uint8_t sf, uint8_t tx) {
     if ( tx > 20 ) return;
     cfg.txpower = tx;
     switch (sf) {
@@ -50,7 +50,7 @@ void switch_lora (int sf, int tx) {
 }
 
 // set of functions that can be triggered by remote commands
-void set_reset(int val) {
+void set_reset(uint8_t val) {
     switch (val) {
         case 0: // restart device
             ESP_LOGI(TAG, "Remote command: restart device");
@@ -72,27 +72,29 @@ void set_reset(int val) {
         }
 };
 
-void set_rssi(int val) {
+void set_rssi(uint8_t val) {
     cfg.rssilimit = val * -1;
     ESP_LOGI(TAG, "Remote command: set RSSI limit to %d", cfg.rssilimit);
 };    
 
-void set_wifiscancycle(int val) {
-    cfg.wifiscancycle = val;
-    ESP_LOGI(TAG, "Remote command: set Wifi scan cycle duration to %d seconds", cfg.wifiscancycle*2);
+void set_sendcycle(uint8_t val) {
+    cfg.sendcycle = val;
+    ESP_LOGI(TAG, "Remote command: set payload send cycle to %d seconds", cfg.sendcycle*2);
 };    
 
-void set_wifichancycle(int val) {
+void set_wifichancycle(uint8_t val) {
     cfg.wifichancycle = val;
-    ESP_LOGI(TAG, "Remote command: set Wifi channel switch interval to %d seconds", cfg.wifichancycle/100);
+    // modify wifi channel rotation IRQ
+    timerAlarmWrite(channelSwitch, cfg.wifichancycle * 10000, true); // reload interrupt after each trigger of channel switch cycle
+    ESP_LOGI(TAG, "Remote command: set Wifi channel switch interval to %.1f seconds", cfg.wifichancycle/float(100));
 };    
 
-void set_blescantime(int val) {
+void set_blescantime(uint8_t val) {
     cfg.blescantime = val;
     ESP_LOGI(TAG, "Remote command: set BLE scan time to %d seconds", cfg.blescantime);
 };
 
-void set_countmode(int val) {
+void set_countmode(uint8_t val) {
     switch (val) {
         case 0: // cyclic unconfirmed
             cfg.countermode = 0; 
@@ -109,7 +111,7 @@ void set_countmode(int val) {
         }
 };
 
-void set_screensaver(int val) {
+void set_screensaver(uint8_t val) {
     ESP_LOGI(TAG, "Remote command: set screen saver to %s ", val ? "on" : "off");
     switch (val) {
         case 1: cfg.screensaver = val; break;
@@ -117,7 +119,7 @@ void set_screensaver(int val) {
         }
 };
 
-void set_display(int val) {
+void set_display(uint8_t val) {
     ESP_LOGI(TAG, "Remote command: set screen to %s", val ? "on" : "off");
     switch (val) {
         case 1: cfg.screenon = val; break;
@@ -125,12 +127,12 @@ void set_display(int val) {
         }
 };
 
-void set_lorasf(int val) {
+void set_lorasf(uint8_t val) {
     ESP_LOGI(TAG, "Remote command: set LoRa SF to %d", val);
     switch_lora(val, cfg.txpower);
 };
 
-void set_loraadr(int val) {
+void set_loraadr(uint8_t val) {
     ESP_LOGI(TAG, "Remote command: set LoRa ADR mode to %s", val ? "on" : "off");
     switch (val) {
         case 1: cfg.adrmode = val; break;
@@ -139,7 +141,7 @@ void set_loraadr(int val) {
     LMIC_setAdrMode(cfg.adrmode); 
 };
 
-void set_blescan(int val) {
+void set_blescan(uint8_t val) {
     ESP_LOGI(TAG, "Remote command: set BLE scan mode to %s", val ? "on" : "off");
     switch (val) {
         case 0:
@@ -152,7 +154,7 @@ void set_blescan(int val) {
         }
 };
 
-void set_wifiant(int val) {
+void set_wifiant(uint8_t val) {
     ESP_LOGI(TAG, "Remote command: set Wifi antenna to %s", val ? "external" : "internal");
     switch (val) {
         case 1: cfg.wifiant = val; break;
@@ -163,7 +165,7 @@ void set_wifiant(int val) {
     #endif
 };
 
-void set_vendorfilter(int val) {
+void set_vendorfilter(uint8_t val) {
     ESP_LOGI(TAG, "Remote command: set vendorfilter mode to %s", val ? "on" : "off");
     switch (val) {
         case 1: cfg.vendorfilter = val; break;
@@ -171,22 +173,22 @@ void set_vendorfilter(int val) {
         }
 };
 
-void set_rgblum(int val) {
+void set_rgblum(uint8_t val) {
     // Avoid wrong parameters
     cfg.rgblum = (val>=0 && val<=100) ? (uint8_t) val : RGBLUMINOSITY;
     ESP_LOGI(TAG, "Remote command: set RGB Led luminosity %d", cfg.rgblum);
 };
 
-void set_lorapower(int val) {
+void set_lorapower(uint8_t val) {
     ESP_LOGI(TAG, "Remote command: set LoRa TXPOWER to %d", val);
     switch_lora(cfg.lorasf, val);
 };
 
-void set_noop (int val) { 
+void set_noop (uint8_t val) { 
     ESP_LOGI(TAG, "Remote command: noop - doing nothing");
 };
 
-void get_config (int val) {
+void get_config (uint8_t val) {
     ESP_LOGI(TAG, "Remote command: get configuration");
     int size = sizeof(configData_t);
     // declare send buffer (char byte array)
@@ -198,7 +200,7 @@ void get_config (int val) {
     ESP_LOGI(TAG, "%d bytes queued in send queue", size-1);
 };
 
-void get_uptime (int val) {
+void get_uptime (uint8_t val) {
     ESP_LOGI(TAG, "Remote command: get uptime");
     int size = sizeof(uptimecounter);
     unsigned char *sendData = new unsigned char[size];
@@ -208,7 +210,7 @@ void get_uptime (int val) {
     ESP_LOGI(TAG, "%d bytes queued in send queue", size-1);
 };
 
-void get_cputemp (int val) {
+void get_cputemp (uint8_t val) {
     ESP_LOGI(TAG, "Remote command: get cpu temperature");
     float temp = temperatureRead();
     int size = sizeof(temp);
@@ -232,7 +234,7 @@ cmd_t table[] = {
                 {0x07, set_loraadr, true},
                 {0x08, set_screensaver, true},
                 {0x09, set_reset, false},
-                {0x0a, set_wifiscancycle, true},
+                {0x0a, set_sendcycle, true},
                 {0x0b, set_wifichancycle, true},
                 {0x0c, set_blescantime, true},
                 {0x0d, set_vendorfilter, false},
@@ -245,7 +247,7 @@ cmd_t table[] = {
                 };
 
 // check and execute remote command
-void rcommand(int cmd, int arg) {
+void rcommand(uint8_t cmd, uint8_t arg) {
     int i = sizeof(table) / sizeof(table[0]); // number of commands in command table
     bool store_flag = false;
     while(i--) {