Initial commit: Simple Sensor firmware for Heltec T114 with BME280

- MeshCore-based Simple Sensor firmware
- Heltec T114 without display
- BME280 sensor support (temp/humidity/pressure)
- Radio: 868.856018 MHz, SF7, BW62.5 kHz, CR4/7
- 2-byte path hash
- PlatformIO project

variants/rak4631/RAK4631Board.h

@@ -0,0 +1,38 @@
+#pragma once
+
+#include <MeshCore.h>
+#include <Arduino.h>
+#include <helpers/NRF52Board.h>
+
+// built-ins
+#define  PIN_VBAT_READ    5
+#define  ADC_MULTIPLIER   (3 * 1.73 * 1.187 * 1000)
+
+class RAK4631Board : public NRF52BoardDCDC {
+protected:
+#ifdef NRF52_POWER_MANAGEMENT
+  void initiateShutdown(uint8_t reason) override;
+#endif
+
+public:
+  RAK4631Board() : NRF52Board("RAK4631_OTA") {}
+  void begin();
+
+  #define BATTERY_SAMPLES 8
+
+  uint16_t getBattMilliVolts() override {
+    analogReadResolution(12);
+
+    uint32_t raw = 0;
+    for (int i = 0; i < BATTERY_SAMPLES; i++) {
+      raw += analogRead(PIN_VBAT_READ);
+    }
+    raw = raw / BATTERY_SAMPLES;
+
+    return (ADC_MULTIPLIER * raw) / 4096;
+  }
+
+  const char* getManufacturerName() const override {
+    return "RAK 4631";
+  }
+};