diff --git a/build.py b/build.py
index 35084709..94b53ff9 100644
--- a/build.py
+++ b/build.py
@@ -74,12 +74,6 @@ board = env.BoardConfig(myboard)
 board.manifest['build']['partitions'] = mypartitiontable
 print('\033[94m' + "Partition table: " + mypartitiontable + '\033[0m')
 
-# set display library
-if "display_library" in mykeys:
-    mydisplay = mykeys["display_library"]
-    env.Append(display_library=mydisplay)
-    print('\033[94m' + "Display library: " + mydisplay + '\033[0m')
-
 # parse ota key file
 with open(otakeyfile) as myfile:
     for line in myfile:
diff --git a/include/bmesensor.h b/include/bmesensor.h
index 5724db84..a038994e 100644
--- a/include/bmesensor.h
+++ b/include/bmesensor.h
@@ -1,6 +1,8 @@
 #ifndef _BMESENSOR_H
 #define _BMESENSOR_H
 
+#if (HAS_BME)
+
 #include <Wire.h>
 
 #include "globals.h"
@@ -53,4 +55,6 @@ int checkIaqSensorStatus(void);
 void loadState(void);
 void updateState(void);
 
+#endif
+
 #endif
\ No newline at end of file
diff --git a/include/dcf77.h b/include/dcf77.h
index df9400e9..6844c1b7 100644
--- a/include/dcf77.h
+++ b/include/dcf77.h
@@ -1,6 +1,8 @@
 #ifndef _DCF77_H
 #define _DCF77_H
 
+#ifdef HAS_DCF77
+
 #include "globals.h"
 #include "timekeeper.h"
 
@@ -15,4 +17,6 @@ enum dcf_pinstate { dcf_low, dcf_high };
 void DCF77_Pulse(uint8_t bit);
 uint64_t DCF77_Frame(const struct tm t);
 
+#endif
+
 #endif
\ No newline at end of file
diff --git a/include/gpsread.h b/include/gpsread.h
index 95cd1afa..6eae7bb7 100644
--- a/include/gpsread.h
+++ b/include/gpsread.h
@@ -1,6 +1,8 @@
 #ifndef _GPSREAD_H
 #define _GPSREAD_H
 
+#if (HAS_GPS)
+
 #include <TinyGPS++.h> // library for parsing NMEA data
 #include <RtcDateTime.h>
 #include "timekeeper.h"
@@ -19,4 +21,6 @@ void gps_storelocation(gpsStatus_t *gps_store);
 void gps_loop(void *pvParameters);
 time_t get_gpstime(uint16_t *msec);
 
+#endif
+
 #endif
\ No newline at end of file
diff --git a/include/hash.h b/include/hash.h
index fe756ec3..fab8df90 100644
--- a/include/hash.h
+++ b/include/hash.h
@@ -4,6 +4,6 @@
 #include <Arduino.h>
 #include <RokkitHash.h>
 
-uint32_t IRAM_ATTR myhash(const char *data, int len);
+uint32_t myhash(const char *data, int len);
 
 #endif
\ No newline at end of file
diff --git a/include/if482.h b/include/if482.h
index 9a3fe92f..4efdbd3f 100644
--- a/include/if482.h
+++ b/include/if482.h
@@ -1,6 +1,8 @@
 #ifndef _IF482_H
 #define _IF482_H
 
+#ifdef HAS_IF482
+
 #include "globals.h"
 #include "timekeeper.h"
 #include "esp_sntp.h"
@@ -10,4 +12,6 @@
 
 String IF482_Frame(time_t t);
 
+#endif
+
 #endif
\ No newline at end of file
diff --git a/include/ledmatrixdisplay.h b/include/ledmatrixdisplay.h
index b27914c1..57b323c0 100644
--- a/include/ledmatrixdisplay.h
+++ b/include/ledmatrixdisplay.h
@@ -1,6 +1,8 @@
 #ifndef _MATRIX_DISPLAY_H
 #define _MATRIX_DISPLAY_H
 
+#ifdef HAS_MATRIX_DISPLAY
+
 #include "LEDMatrix.h"
 #include "ledmatrixfonts.h"
 #include "ledmatrixdisplay.h"
@@ -16,4 +18,6 @@ uint8_t GetCharFromFont(char cChar);
 uint8_t GetCharWidth(char cChar);
 void ScrollMatrixLeft(uint8_t *buf, const uint16_t cols, const uint16_t rows);
 
+#endif
+
 #endif
\ No newline at end of file
diff --git a/include/lorawan.h b/include/lorawan.h
index 0c870bb9..32ddc4ba 100644
--- a/include/lorawan.h
+++ b/include/lorawan.h
@@ -38,10 +38,10 @@ void lora_send(void *pvParameters);
 void lora_enqueuedata(MessageBuffer_t *message);
 void lora_queuereset(void);
 uint32_t lora_queuewaiting(void);
-void IRAM_ATTR myEventCallback(void *pUserData, ev_t ev);
-void IRAM_ATTR myRxCallback(void *pUserData, uint8_t port, const uint8_t *pMsg,
+void myEventCallback(void *pUserData, ev_t ev);
+void myRxCallback(void *pUserData, uint8_t port, const uint8_t *pMsg,
                             size_t nMsg);
-void IRAM_ATTR myTxCallback(void *pUserData, int fSuccess);
+void myTxCallback(void *pUserData, int fSuccess);
 const char *getSfName(rps_t rps);
 const char *getBwName(rps_t rps);
 const char *getCrName(rps_t rps);
diff --git a/include/mqttclient.h b/include/mqttclient.h
index 6151dd52..cfdad89f 100644
--- a/include/mqttclient.h
+++ b/include/mqttclient.h
@@ -1,6 +1,8 @@
 #ifndef _MQTTCLIENT_H
 #define _MQTTCLIENT_H
 
+#ifdef HAS_MQTT
+
 #include "globals.h"
 #include "rcommand.h"
 #include "hash.h"
@@ -24,4 +26,6 @@ void NetworkEvent(WiFiEvent_t event);
 esp_err_t mqtt_init(void);
 void mqtt_deinit(void);
 
+#endif
+
 #endif // _MQTTCLIENT_H
\ No newline at end of file
diff --git a/include/power.h b/include/power.h
index 0e123c98..24f6fb67 100644
--- a/include/power.h
+++ b/include/power.h
@@ -3,7 +3,6 @@
 
 #include <Arduino.h>
 #include <esp_adc_cal.h>
-//include <esp32-hal-adc.h>
 #include <soc/adc_channel.h>
 
 #include "i2c.h"
@@ -56,7 +55,6 @@ void calibrate_voltage(void);
 bool batt_sufficient(void);
 
 #ifdef HAS_PMU
-
 #include <axp20x.h>
 extern AXP20X_Class pmu;
 enum pmu_power_t { pmu_power_on, pmu_power_off, pmu_power_sleep };
@@ -64,7 +62,6 @@ void AXP192_powerevent_IRQ(void);
 void AXP192_power(pmu_power_t powerlevel);
 void AXP192_init(void);
 void AXP192_showstatus(void);
-
 #endif // HAS_PMU
 
 #ifdef HAS_IP5306
diff --git a/include/rcommand.h b/include/rcommand.h
index d842fdef..e01369b1 100644
--- a/include/rcommand.h
+++ b/include/rcommand.h
@@ -34,7 +34,7 @@ typedef struct {
   uint8_t cmdLen;
 } RcmdBuffer_t;
 
-void IRAM_ATTR rcommand(const uint8_t *cmd, const size_t cmdlength);
+void rcommand(const uint8_t *cmd, const size_t cmdlength);
 void rcmd_queuereset(void);
 uint32_t rcmd_queuewaiting(void);
 void rcmd_deinit(void);
diff --git a/include/rtctime.h b/include/rtctime.h
index 3f75eb37..802b06ee 100644
--- a/include/rtctime.h
+++ b/include/rtctime.h
@@ -1,6 +1,8 @@
 #ifndef _RTCTIME_H
 #define _RTCTIME_H
 
+#ifdef HAS_RTC
+
 #include <Wire.h> // must be included here so that Arduino library object file references work
 #include <RtcDS3231.h>
 
@@ -15,4 +17,6 @@ void sync_rtctime(void);
 time_t get_rtctime(uint16_t *msec);
 float get_rtctemp(void);
 
+#endif
+
 #endif // _RTCTIME_H
\ No newline at end of file
diff --git a/include/sdcard.h b/include/sdcard.h
index 25fcf2c4..1f2b0bca 100644
--- a/include/sdcard.h
+++ b/include/sdcard.h
@@ -1,23 +1,18 @@
 #ifndef _SDCARD_H
 #define _SDCARD_H
 
+#if (HAS_SDCARD)
+
 #include "globals.h"
 #include <stdio.h>
 #include <SPI.h>
+#include "esp_vfs_fat.h"
+#include "sdmmc_cmd.h"
 
-#if (HAS_SDCARD)
-#if HAS_SDCARD == 1
-#include <SD.h>
-#elif HAS_SDCARD == 2
-#include <SD_MMC.h>
-#else
-#error HAS_SDCARD unknown card reader value, must be either 1 or 2
-#endif
-#endif
+#define MOUNT_POINT "/sdcard"
 
-#ifdef HAS_SDS011
-#include "sds011read.h"
-#endif
+#if HAS_SDCARD == 1 // SPI interface
+#include "driver/sdspi_host.h"
 
 #ifndef SDCARD_CS
 #define SDCARD_CS SS
@@ -35,23 +30,23 @@
 #define SDCARD_SCLK SCK
 #endif
 
-// Default config for SDMMC_HOST_DEFAULT (4-bit bus width, slot 1)
-// https://docs.espressif.com/projects/esp-idf/en/latest/esp32/api-reference/peripherals/sdmmc_host.html
+#elif HAS_SDCARD == 2 // MMC interface
+#include "driver/sdmmc_host.h"
 
-#ifndef SDCARD_DATA0
-#define SDCARD_DATA0 2
+#ifndef SDCARD_SLOTWIDTH
+#define SDCARD_SLOTWIDTH 1
 #endif
 
-#ifndef SDCARD_DATA1
-#define SDCARD_DATA1 4
+#ifndef SDCARD_PULLUP
+#define SDCARD_PULLUP SDMMC_SLOT_FLAG_INTERNAL_PULLUP
 #endif
 
-#ifndef SDCARD_DATA2
-#define SDCARD_DATA2 12
+#else
+#error HAS_SDCARD unknown card reader value, must be either 1 or 2
 #endif
 
-#ifndef SDCARD_DATA3
-#define SDCARD_DATA3 13
+#ifdef HAS_SDS011
+#include "sds011read.h"
 #endif
 
 #define SDCARD_FILE_NAME clientId
@@ -62,7 +57,10 @@
 #endif
 
 bool sdcard_init(bool create = true);
+void sdcard_flush(void);
 void sdcard_close(void);
 void sdcardWriteData(uint16_t, uint16_t, uint16_t = 0);
 
+#endif
+
 #endif // _SDCARD_H
diff --git a/include/sds011read.h b/include/sds011read.h
index f1b874d3..6345a267 100644
--- a/include/sds011read.h
+++ b/include/sds011read.h
@@ -1,10 +1,12 @@
 #ifndef _SDS011READ_H
 #define _SDS011READ_H
 
+#if (HAS_SDS011)
+
 #include <SdsDustSensor.h>
 #include "globals.h"
 
-#define SDCARD_FILE_HEADER_SDS011     ", PM10,PM25"
+#define SDCARD_FILE_HEADER_SDS011 ", PM10,PM25"
 
 // use original pins from HardwareSerial if none defined
 #ifndef SDS_TX
@@ -21,4 +23,7 @@ void sds011_loop();
 void sds011_sleep(void);
 void sds011_wakeup(void);
 void sds011_store(sdsStatus_t *sds_store);
+
+#endif
+
 #endif // _SDS011READ_H
diff --git a/include/spislave.h b/include/spislave.h
index 78b7a737..389aa573 100644
--- a/include/spislave.h
+++ b/include/spislave.h
@@ -24,6 +24,8 @@ licenses. Refer to LICENSE.txt file in repository for more details.
 #ifndef _SPISLAVE_H
 #define _SPISLAVE_H
 
+#ifdef HAS_SPI
+
 #include "globals.h"
 #include "rcommand.h"
 
@@ -35,4 +37,6 @@ void spi_enqueuedata(MessageBuffer_t *message);
 uint32_t spi_queuewaiting(void);
 void spi_queuereset(void);
 
+#endif
+
 #endif // _SPISLAVE_H
diff --git a/include/timekeeper.h b/include/timekeeper.h
index ee20913e..e28b60d9 100644
--- a/include/timekeeper.h
+++ b/include/timekeeper.h
@@ -34,7 +34,7 @@ void setTimeSyncIRQ(void);
 uint8_t timepulse_init(void);
 bool timeIsValid(time_t const t);
 void calibrateTime(void);
-bool IRAM_ATTR setMyTime(uint32_t t_sec, uint16_t t_msec,
+bool setMyTime(uint32_t t_sec, uint16_t t_msec,
                          timesource_t mytimesource);
 time_t compileTime(void);
 time_t mkgmtime(const struct tm *ptm);
diff --git a/include/timesync.h b/include/timesync.h
index cd517421..f12f70ec 100644
--- a/include/timesync.h
+++ b/include/timesync.h
@@ -21,7 +21,7 @@ enum timesync_t {
 void timesync_init(void);
 void timesync_request(void);
 void timesync_store(uint32_t timestamp, timesync_t timestamp_type);
-void IRAM_ATTR timesync_processReq(void *taskparameter);
-void IRAM_ATTR timesync_serverAnswer(void *pUserData, int flag);
+void timesync_processReq(void *taskparameter);
+void timesync_serverAnswer(void *pUserData, int flag);
 
 #endif
diff --git a/platformio_orig.ini b/platformio_orig.ini
index 2c2112cf..c9dc8755 100644
--- a/platformio_orig.ini
+++ b/platformio_orig.ini
@@ -1,10 +1,8 @@
-; PlatformIO Project Configuration File
+; ---> SELECT ONE TARGET BOARD FROM FOLLOWING ROWS <---
+;
+; Note: For "LILYGO TTGO ESP32-Paxcounter LoRa32 V2.1 1.6.1" select board ttgov21new.h
+;
 ;
-; Please visit documentation for the other options and examples
-; http://docs.platformio.org/page/projectconf.html
-
-
-; ---> SELECT THE TARGET PLATFORM HERE! <---
 [board]
 ;halfile = generic.h
 ;halfile = ebox.h
@@ -100,8 +98,6 @@ build_flags_basic =
     '-DCORE_DEBUG_LEVEL=${common.debug_level}'
     '-DLOG_LOCAL_LEVEL=${common.debug_level}'
     '-DPROGVERSION="${common.release_version}"'
-    '-Wno-unknown-pragmas'
-    '-Wno-unused-variable'
     '-D LIBPAX_WIFI'
     '-D LIBPAX_BLE'
     '-D LIBPAX_ARDUINO'
@@ -113,6 +109,7 @@ build_flags_all =
 framework = arduino
 board = esp32dev
 board_build.partitions = min_spiffs.csv
+build_type = release
 upload_speed = ${common.upload_speed}
 ;upload_port = COM12
 platform = ${common.platform_espressif32}
diff --git a/src/antenna.cpp b/src/antenna.cpp
index 9f6a8a9b..5e3b0bd8 100644
--- a/src/antenna.cpp
+++ b/src/antenna.cpp
@@ -5,7 +5,7 @@
 #include <Arduino.h>
 
 // Local logging tag
-static const char TAG[] = "wifi";
+static const char TAG[] = __FILE__;
 
 typedef enum { ANTENNA_INT = 0, ANTENNA_EXT } antenna_type_t;
 
diff --git a/src/cyclic.cpp b/src/cyclic.cpp
index 385f9afe..27697efc 100644
--- a/src/cyclic.cpp
+++ b/src/cyclic.cpp
@@ -126,6 +126,10 @@ void doHousekeeping() {
   }
 #endif
 
+#if (HAS_SDCARD)
+  sdcard_flush();
+#endif
+
 } // doHousekeeping()
 
 uint32_t getFreeRAM() {
diff --git a/src/hal/ttgov21new.h b/src/hal/ttgov21new.h
index fbaae22b..47145374 100644
--- a/src/hal/ttgov21new.h
+++ b/src/hal/ttgov21new.h
@@ -9,14 +9,15 @@
 
 /*  Hardware related definitions for TTGO V2.1 Board
 // ATTENTION: check your board version!
-// This settings are for boards labeled v1.6 on pcb, NOT for v1.5 or older
+// This settings are for boards labeled v1.6 or v1.6.1 on pcb, NOT for v1.5 or older
 */
 
 #define HAS_LORA         1 // comment out if device shall not send data via LoRa
 #define CFG_sx1276_radio 1 // HPD13A LoRa SoC
 
 // enable only if you want to store a local paxcount table on the device
-#define HAS_SDCARD  2      // this board has a SDMMC card-reader/writer
+#define HAS_SDCARD  2      // this board has a SD MMC card-reader/writer
+#define SDCARD_SLOTWIDTH 4 // 4-line interface
 
 #define HAS_DISPLAY 1
 #define HAS_LED (25) // green on board LED
diff --git a/src/hash.cpp b/src/hash.cpp
index 78f31d03..864a51cd 100644
--- a/src/hash.cpp
+++ b/src/hash.cpp
@@ -40,6 +40,6 @@
 #undef ROKKIT_ENABLE_8BIT_OPTIMIZATIONS
 #endif
 
-uint32_t IRAM_ATTR myhash(const char *data, int len) {
+uint32_t myhash(const char *data, int len) {
   return rokkit(data, len);
 }
diff --git a/src/i2c.cpp b/src/i2c.cpp
index 538d1681..c908d250 100644
--- a/src/i2c.cpp
+++ b/src/i2c.cpp
@@ -53,7 +53,7 @@ void i2c_scan(void) {
   if (I2C_MUTEX_LOCK()) {
 
     memset(&bbi2c, 0, sizeof(bbi2c));
-    bbi2c.bWire = 1; // use wire library, no bitbanging
+    bbi2c.bWire = 0;
     bbi2c.iSDA = MY_DISPLAY_SDA;
     bbi2c.iSCL = MY_DISPLAY_SCL;
     I2CInit(&bbi2c, 100000L); // Scan at 100KHz low speed
diff --git a/src/lorawan.cpp b/src/lorawan.cpp
index 299481fc..1d40e5eb 100644
--- a/src/lorawan.cpp
+++ b/src/lorawan.cpp
@@ -4,7 +4,7 @@
 #include "lorawan.h"
 
 // Local logging Tag
-static const char TAG[] = "lora";
+static const char TAG[] = __FILE__;
 
 #if CLOCK_ERROR_PROCENTAGE > 7
 #warning CLOCK_ERROR_PROCENTAGE value in lmic_config.h is too high; values > 7 will cause side effects
diff --git a/src/rcommand.cpp b/src/rcommand.cpp
index 1654b345..639e6c84 100644
--- a/src/rcommand.cpp
+++ b/src/rcommand.cpp
@@ -84,8 +84,7 @@ void set_sendcycle(uint8_t val[]) {
 
 void set_sleepcycle(uint8_t val[]) {
   // swap byte order from msb to lsb, note: this is a platform dependent hack
-  uint16_t t = __builtin_bswap16(*(uint16_t *)(val));
-  cfg.sleepcycle = t;
+  cfg.sleepcycle = __builtin_bswap16(*(uint16_t *)(val));
   ESP_LOGI(TAG, "Remote command: set sleep cycle to %d seconds",
            cfg.sleepcycle * 10);
 }
@@ -485,7 +484,7 @@ void rcmd_process(void *pvParameters) {
 } // rcmd_process()
 
 // enqueue remote command
-void IRAM_ATTR rcommand(const uint8_t *cmd, const size_t cmdlength) {
+void rcommand(const uint8_t *cmd, const size_t cmdlength) {
 
   RcmdBuffer_t rcmd = {0};
 
diff --git a/src/rtctime.cpp b/src/rtctime.cpp
index eb25698d..9b12cd94 100644
--- a/src/rtctime.cpp
+++ b/src/rtctime.cpp
@@ -1,10 +1,10 @@
+#ifdef HAS_RTC // we have hardware RTC
+
 #include "rtctime.h"
 
 // Local logging tag
 static const char TAG[] = __FILE__;
 
-#ifdef HAS_RTC // we have hardware RTC
-
 RtcDS3231<TwoWire> Rtc(Wire); // RTC hardware i2c interface
 
 // initialize RTC
diff --git a/src/sdcard.cpp b/src/sdcard.cpp
index c8696bb1..4794ce00 100644
--- a/src/sdcard.cpp
+++ b/src/sdcard.cpp
@@ -1,156 +1,267 @@
+#ifdef HAS_SDCARD
+
 // routines for writing data to an SD-card, if present
 // use FAT32 formatted card
 // check whether your card reader supports SPI oder SDMMC and select appropriate
-// SD low level driver in board hal file
+// SD interface in board hal file
 
 // Local logging tag
 static const char TAG[] = __FILE__;
 
 #include "sdcard.h"
 
-#ifdef HAS_SDCARD
+sdmmc_card_t *card;
 
-static bool useSDCard;
-static void openFile(void);
+const char mount_point[] = MOUNT_POINT;
+static bool useSDCard = false;
 
-File fileSDCard;
+// This file stream will be used for payload logging
+static FILE *data_file;
+// This file stream will be used for system logging
 
-#if HAS_SDCARD == 1
-SPIClass sd_spi;
+#ifdef SD_LOGGING
+static FILE *log_file;
+
+// Save UART stdout stream
+static FILE *uart_stdout = stdout;
+
+// This function will be called by the ESP log library every time ESP_LOG needs
+// to be performed.
+//      @important Do NOT use the ESP_LOG* macro's in this function ELSE
+//      recursive loop and stack overflow! So use printf() instead for debug
+//      messages.
+// CURRENTLY NOT WORKING DUE TO AN ISSUE IN ARDUINO-ESP32
+int print_to_sd_card(const char *fmt, va_list args) {
+  static bool static_fatal_error = false;
+  static const uint32_t WRITE_CACHE_CYCLE = 5;
+  static uint32_t counter_write = 0;
+  int iresult;
+
+  // #1 Write to file
+  if (log_file == NULL) {
+    printf("%s() ABORT. file handle log_file is NULL\n", __FUNCTION__);
+    return -1;
+  }
+  if (static_fatal_error == false) {
+    iresult = vfprintf(log_file, fmt, args);
+    if (iresult < 0) {
+      printf("%s() ABORT. failed vfprintf() -> logging disabled \n",
+             __FUNCTION__);
+      // MARK FATAL
+      static_fatal_error = true;
+      return iresult;
+    }
+
+    // #2 Smart commit after x writes
+    counter_write++;
+    if (counter_write % WRITE_CACHE_CYCLE == 0) {
+      printf("%s() fsync'ing log file (WRITE_CACHE_CYCLE=%u)\n",
+             WRITE_CACHE_CYCLE);
+      fsync(fileno(log_file));
+    }
+  }
+
+  // #3 ALWAYS Write to stdout!
+  return vprintf(fmt, args);
+}
 #endif
 
+bool openFile(FILE **fd, const char *filename) {
+
+  char _filename[50];
+  sprintf(_filename, "%s%s", MOUNT_POINT, filename);
+
+  if ((*fd = fopen(_filename, "a")) == NULL) {
+    ESP_LOGE(TAG, "file <%s> open error", _filename);
+    return false;
+  } else {
+    ESP_LOGI(TAG, "file <%s> opened", _filename);
+    return true;
+  }
+} // openfile
+
 bool sdcard_init(bool create) {
 
+  esp_err_t ret;
+
   // for usage of SD drivers on ESP32 platform see
   // https://docs.espressif.com/projects/esp-idf/en/latest/esp32/api-reference/peripherals/sdspi_host.html
   // https://docs.espressif.com/projects/esp-idf/en/latest/esp32/api-reference/peripherals/sdmmc_host.html
 
-  ESP_LOGI(TAG, "looking for SD-card...");
-#if HAS_SDCARD == 1 // use SD SPI host driver
-  digitalWrite(SDCARD_CS, HIGH);
-  sd_spi.begin(SDCARD_SCLK, SDCARD_MISO, SDCARD_MOSI, SDCARD_CS);
-  digitalWrite(SDCARD_CS, LOW);
-  useSDCard = SD.begin(SDCARD_CS, sd_spi);
-#elif HAS_SDCARD == 2 // use SD MMC host driver
-  // enable internal pullups of sd-data lines
-  gpio_set_pull_mode(gpio_num_t(SDCARD_DATA0), GPIO_PULLUP_ONLY);
-  gpio_set_pull_mode(gpio_num_t(SDCARD_DATA1), GPIO_PULLUP_ONLY);
-  gpio_set_pull_mode(gpio_num_t(SDCARD_DATA2), GPIO_PULLUP_ONLY);
-  gpio_set_pull_mode(gpio_num_t(SDCARD_DATA3), GPIO_PULLUP_ONLY);
-  useSDCard = SD_MMC.begin();
-#endif
+  // Options for mounting the filesystem.
+  // If format_if_mount_failed is set to true, SD card will be partitioned and
+  // formatted in case when mounting fails.
+  esp_vfs_fat_mount_config_t mount_config = {.format_if_mount_failed = false,
+                                             .max_files = 5};
 
-  if (useSDCard) {
-    ESP_LOGI(TAG, "SD-card found");
-    openFile();
-    return true;
-  } else {
-    ESP_LOGI(TAG, "SD-card not found");
+  ESP_LOGI(TAG, "looking for SD-card...");
+
+#if (HAS_SDCARD == 1) // use SD interface in SPI host mode
+
+  sdmmc_host_t host = SDSPI_HOST_DEFAULT();
+
+  spi_bus_config_t bus_cfg = {
+      .mosi_io_num = (gpio_num_t)SDCARD_MOSI,
+      .miso_io_num = (gpio_num_t)SDCARD_MISO,
+      .sclk_io_num = (gpio_num_t)SDCARD_SCLK,
+      .quadwp_io_num = -1,
+      .quadhd_io_num = -1,
+      .max_transfer_sz = 4000,
+  };
+
+  // This initializes the slot without card detect (CD) and write protect (WP)
+  // signals. Modify slot_config.gpio_cd and slot_config.gpio_wp if you want
+  // to use these signals (if your board has them)
+  sdspi_device_config_t slot_config = SDSPI_DEVICE_CONFIG_DEFAULT();
+  slot_config.gpio_cs = (gpio_num_t)SDCARD_CS;
+
+  ret = spi_bus_initialize(SPI_HOST, &bus_cfg, 1);
+  if (ret != ESP_OK) {
+    ESP_LOGE(TAG, "failed to initialize SPI bus");
     return false;
   }
+
+  // Use settings defined above to initialize SD card and mount FAT filesystem.
+  ret = esp_vfs_fat_sdspi_mount(mount_point, &host, &slot_config, &mount_config,
+                                &card);
+
+#elif (HAS_SDCARD == 2) // use SD interface in MMC host mode
+
+  sdmmc_host_t host = SDMMC_HOST_DEFAULT();
+
+  // This initializes the slot without card detect (CD) and write protect (WP)
+  // signals. Modify slot_config.gpio_cd and slot_config.gpio_wp if your board
+  // has these signals.
+  // Default config for SDMMC_HOST_DEFAULT (4-bit bus width, slot 1)
+  // https://docs.espressif.com/projects/esp-idf/en/latest/esp32/api-reference/peripherals/sdmmc_host.html
+  sdmmc_slot_config_t slot_config = SDMMC_SLOT_CONFIG_DEFAULT();
+
+  // Set 1-line or 4-line SD mode (default is 1-line)
+  slot_config.width = SDCARD_SLOTWIDTH;
+
+  // Enable internal pullups on enabled pins. The internal pullups
+  // are insufficient however, please make sure 10k external pullups are
+  // connected on the bus. This is for debug / example purpose only.
+  slot_config.flags |= SDCARD_PULLUP;
+
+  // Use settings defined above to initialize SD card and mount FAT filesystem.
+  ret = esp_vfs_fat_sdmmc_mount(mount_point, &host, &slot_config, &mount_config,
+                                &card);
+
+#endif
+
+  // mount error handling
+  if (ret != ESP_OK) {
+    if (ret == ESP_FAIL) {
+      ESP_LOGE(TAG, "failed to mount filesystem");
+    } else {
+      ESP_LOGE(TAG, "SD-card not found (%d)", ret);
+    }
+    return false;
+  }
+
+  // SD card is now initialized
+  useSDCard = true;
+  ESP_LOGI(TAG, "filesystem mounted");
+  sdmmc_card_print_info(stdout, card);
+
+  // open files for data and, optional, system logging
+  char bufferFilename[50];
+
+  snprintf(bufferFilename, sizeof(bufferFilename), "/%s.csv", SDCARD_FILE_NAME);
+
+  if (openFile(&data_file, bufferFilename)) {
+
+    fpos_t position;
+    fgetpos(data_file, &position);
+
+    // empty file? then we write a header line
+    if (position == 0) {
+      fprintf(data_file, "%s", SDCARD_FILE_HEADER);
+#if (defined BAT_MEASURE_ADC || defined HAS_PMU)
+      fprintf(data_file, "%s", SDCARD_FILE_HEADER_VOLTAGE);
+#endif
+#if (HAS_SDS011)
+      fprintf(data_file, "%s", SDCARD_FILE_HEADER_SDS011);
+#endif
+    }
+    fprintf(data_file, "\n");
+
+  } else {
+    useSDCard = false;
+  }
+
+#ifdef SD_LOGGING
+  snprintf(bufferFilename, sizeof(bufferFilename), "/%s.log", SDCARD_FILE_NAME);
+
+  if (openFile(&log_file, bufferFilename)) {
+    ESP_LOGI(TAG, "redirecting serial output to SD-card");
+    esp_log_set_vprintf(&print_to_sd_card);
+    // Change stdout for THIS TASK ONLY
+    // stdout = log_file;
+    // Change stdout for all new tasks which will be created
+    //_GLOBAL_REENT->_stdout = log_file;
+  } else {
+    useSDCard = false;
+  }
+#endif
+
+  return useSDCard;
+
+} // sdcard_init
+
+void sdcard_flush(void) {
+  if (data_file)
+    fsync(fileno(data_file));
+#ifdef SD_LOGGING
+  if (log_file)
+    fsync(fileno(log_file));
+#endif
 }
 
 void sdcard_close(void) {
   ESP_LOGI(TAG, "closing SD-card");
-  fileSDCard.flush();
-  fileSDCard.close();
+  sdcard_flush();
+#ifdef SD_LOGGING
+  // Reset logging output back to normal
+  ESP_LOGI(TAG, "redirect console back to serial output");
+  // stdout = uart_stdout;
+  //_GLOBAL_REENT->_stdout = uart_stdout;
+  esp_log_set_vprintf(&vprintf);
+#endif
+  fcloseall();
+  esp_vfs_fat_sdcard_unmount(mount_point, card);
+  ESP_LOGI(TAG, "SD-card unmounted");
 }
 
 void sdcardWriteData(uint16_t noWifi, uint16_t noBle,
                      __attribute__((unused)) uint16_t voltage) {
-  static int counterWrites = 0;
-  char tempBuffer[20 + 1];
+
+  if (!useSDCard)
+    return;
+
+  char timeBuffer[20 + 1];
   time_t t = time(NULL);
   struct tm tt;
   gmtime_r(&t, &tt); // make UTC timestamp
+  strftime(timeBuffer, sizeof(timeBuffer), "%FT%TZ", &tt);
 
 #if (HAS_SDS011)
   sdsStatus_t sds;
 #endif
 
-  if (!useSDCard)
-    return;
+  ESP_LOGI(TAG, "writing data to SD-card");
 
-  ESP_LOGI(TAG, "SD: writing data");
-  strftime(tempBuffer, sizeof(tempBuffer), "%FT%TZ", &tt);
-  fileSDCard.print(tempBuffer);
-  snprintf(tempBuffer, sizeof(tempBuffer), ",%d,%d", noWifi, noBle);
-  fileSDCard.print(tempBuffer);
+  fprintf(data_file, "%s", timeBuffer);
+  fprintf(data_file, ",%d,%d", noWifi, noBle);
 #if (defined BAT_MEASURE_ADC || defined HAS_PMU)
-  snprintf(tempBuffer, sizeof(tempBuffer), ",%d", voltage);
-  fileSDCard.print(tempBuffer);
+  fprintf(data_file, ",%d", voltage);
 #endif
 #if (HAS_SDS011)
   sds011_store(&sds);
-  snprintf(tempBuffer, sizeof(tempBuffer), ",%5.1f,%4.1f", sds.pm10 / 10,
-           sds.pm25 / 10);
-  fileSDCard.print(tempBuffer);
+  fprintf(data_file, ",%5.1f,%4.1f", sds.pm10 / 10, sds.pm25 / 10);
 #endif
-  fileSDCard.println();
-
-  if (++counterWrites > 2) {
-    // force writing to SD-card
-    ESP_LOGI(TAG, "SD: flushing data");
-    fileSDCard.flush();
-    counterWrites = 0;
-  }
-}
-
-void openFile(void) {
-  char bufferFilename[30];
-
-  useSDCard = false;
-
-  snprintf(bufferFilename, sizeof(bufferFilename), "/%s.csv", SDCARD_FILE_NAME);
-  ESP_LOGI(TAG, "SD: looking for file <%s>", bufferFilename);
-
-#if HAS_SDCARD == 1
-  bool fileExists = SD.exists(bufferFilename);
-#elif HAS_SDCARD == 2
-  bool fileExists = SD_MMC.exists(bufferFilename);
-#endif
-
-  // file not exists, create it
-  if (!fileExists) {
-    ESP_LOGD(TAG, "SD: file not found, creating...");
-
-#if HAS_SDCARD == 1
-    fileSDCard = SD.open(bufferFilename, FILE_WRITE);
-#elif HAS_SDCARD == 2
-    fileSDCard = SD_MMC.open(bufferFilename, FILE_WRITE);
-#endif
-
-    if (fileSDCard) {
-      ESP_LOGD(TAG, "SD: name opened: <%s>", bufferFilename);
-      fileSDCard.print(SDCARD_FILE_HEADER);
-#if (defined BAT_MEASURE_ADC || defined HAS_PMU)
-      fileSDCard.print(SDCARD_FILE_HEADER_VOLTAGE); // for battery level data
-#endif
-#if (HAS_SDS011)
-      fileSDCard.print(SDCARD_FILE_HEADER_SDS011);
-#endif
-      fileSDCard.println();
-      useSDCard = true;
-    }
-  }
-
-  // file exists, append data
-  else {
-    ESP_LOGD(TAG, "SD: file found, opening...");
-
-#if HAS_SDCARD == 1
-    fileSDCard = SD.open(bufferFilename, FILE_APPEND);
-#elif HAS_SDCARD == 2
-    fileSDCard = SD_MMC.open(bufferFilename, FILE_APPEND);
-#endif
-
-    if (fileSDCard) {
-      ESP_LOGD(TAG, "SD: name opened: <%s>", bufferFilename);
-      useSDCard = true;
-    }
-  }
-
-  return;
+  fprintf(data_file, "\n");
 }
 
 #endif // (HAS_SDCARD)
diff --git a/src/senddata.cpp b/src/senddata.cpp
index fedee7da..d55ee92c 100644
--- a/src/senddata.cpp
+++ b/src/senddata.cpp
@@ -1,6 +1,9 @@
 // Basic Config
 #include "senddata.h"
 
+// Local logging tag
+static const char TAG[] = __FILE__;
+
 void setSendIRQ(TimerHandle_t xTimer) {
   xTaskNotify(irqHandlerTask, SENDCYCLE_IRQ, eSetBits);
 }
diff --git a/src/timekeeper.cpp b/src/timekeeper.cpp
index d51d1570..32b1e0fe 100644
--- a/src/timekeeper.cpp
+++ b/src/timekeeper.cpp
@@ -63,7 +63,7 @@ void calibrateTime(void) {
 } // calibrateTime()
 
 // set system time (UTC), calibrate RTC and RTC_INT pps
-bool IRAM_ATTR setMyTime(uint32_t t_sec, uint16_t t_msec,
+bool setMyTime(uint32_t t_sec, uint16_t t_msec,
                          timesource_t mytimesource) {
 
   struct timeval tv = {0};
diff --git a/src/timesync.cpp b/src/timesync.cpp
index 80355eb8..8660c597 100644
--- a/src/timesync.cpp
+++ b/src/timesync.cpp
@@ -55,7 +55,7 @@ void timesync_request(void) {
 }
 
 // task for processing time sync request
-void IRAM_ATTR timesync_processReq(void *taskparameter) {
+void timesync_processReq(void *taskparameter) {
 
   uint32_t rcv_seqNo = TIME_SYNC_END_FLAG;
   uint32_t time_offset_sec = 0, time_offset_ms = 0;
@@ -173,7 +173,7 @@ void timesync_store(uint32_t timestamp, timesync_t timestamp_type) {
 }
 
 // callback function to receive time answer from network or answer
-void IRAM_ATTR timesync_serverAnswer(void *pUserData, int flag) {
+void timesync_serverAnswer(void *pUserData, int flag) {
 
 #if (HAS_LORA_TIME)