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/rak11310/RAK11310Board.h

@@ -0,0 +1,49 @@
+#pragma once
+
+#include <Arduino.h>
+#include <MeshCore.h>
+
+// from https://github.com/RAKWireless/RAK11300-AT-Command-Firmware/blob/9c48409a43620a828d653501d536473200aa33af/RAK11300-AT-Arduino/batt.cpp#L17-L19
+#define VBAT_MV_PER_LSB (0.806F)   // 3.0V ADC range and 12 - bit ADC resolution = 3300mV / 4096
+#define VBAT_DIVIDER (0.6F)		   // 1.5M + 1M voltage divider on VBAT = (1.5M / (1M + 1.5M))
+#define VBAT_DIVIDER_COMP (1.846F) //  // Compensation factor for the VBAT divider
+
+#define PIN_VBAT_READ            26
+#define BATTERY_SAMPLES          8
+#define ADC_MULTIPLIER           (VBAT_DIVIDER_COMP * VBAT_MV_PER_LSB)
+
+class RAK11310Board : public mesh::MainBoard {
+protected:
+  uint8_t startup_reason;
+
+public:
+  void begin();
+  uint8_t getStartupReason() const override { return startup_reason; }
+
+#ifdef P_LORA_TX_LED
+  void onBeforeTransmit() override { digitalWrite(P_LORA_TX_LED, HIGH); }
+  void onAfterTransmit() override { digitalWrite(P_LORA_TX_LED, LOW); }
+#endif
+
+  uint16_t getBattMilliVolts() override {
+#if defined(PIN_VBAT_READ) && defined(ADC_MULTIPLIER)
+    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);
+#else
+    return 0;
+#endif
+  }
+
+  const char *getManufacturerName() const override { return "RAK 11310"; }
+
+  void reboot() override { rp2040.reboot(); }
+
+  bool startOTAUpdate(const char *id, char reply[]) override;
+};