Improve power usage by ~20mA by reducing CPU clock

src/LoRa_APRS_Tracker.cpp

@@ -4,9 +4,14 @@
 #include <OneButton.h>
 #include <TimeLib.h>
 #include <TinyGPS++.h>
-#include <WiFi.h>
+#ifdef ESP32
+# include <WiFi.h>
+#endif
 #include <logger.h>
-
+#ifdef ESP32
+#  include <driver/adc.h>
+#  include <esp_bt.h>
+#endif
 #include "BeaconManager.h"
 #include "configuration.h"
 #include "display.h"
@@ -91,10 +96,26 @@ void setup() {
     digitalWrite(Config.ptt.io_pin, Config.ptt.reverse ? HIGH : LOW);
   }
 
+#ifdef ESP32
   // make sure wifi and bt is off as we don't need it:
   WiFi.mode(WIFI_OFF);
   btStop();
 
+  esp_bt_controller_disable();
+#  if defined(TTGO_T_Beam_V1_0) // || defined(TTGO_T_Beam_V0_7)
+  // TTGO_T_Beam_V0_7 should probably work as well but could not be confirmed so it is disabled now
+  // We don't need built-in ADC for voltage measurement on T-beam 1.0
+  adc_power_off();
+
+  //Going to 20MHz breaks the display, 40 MHz reduces power consumption by ~15-20mA
+  if (! setCpuFrequencyMhz(40)) {
+    setCpuFrequencyMhz(80); // Some guides suggest this as backup for other CPUs
+    logPrintlnD("Setting CPU frequency to 80Mhz");
+  } else {
+    logPrintlnD("Setting CPU frequency to 40Mhz");
+  }
+#  endif
+#endif
   if (Config.button.tx) {
     // attach TX action to user button (defined by BUTTON_PIN)
     userButton.attachClick(handle_tx_click);