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/heltec_t114/T114Board.h

@@ -0,0 +1,59 @@
+#pragma once
+
+#include <MeshCore.h>
+#include <Arduino.h>
+#include <helpers/NRF52Board.h>
+
+// built-ins
+#define  PIN_VBAT_READ    4
+#define  PIN_BAT_CTL      6
+#define  MV_LSB   (3000.0F / 4096.0F) // 12-bit ADC with 3.0V input range
+
+class T114Board : public NRF52BoardDCDC {
+protected:
+#ifdef NRF52_POWER_MANAGEMENT
+  void initiateShutdown(uint8_t reason) override;
+#endif
+
+public:
+  T114Board() : NRF52Board("T114_OTA") {}
+  void begin();
+
+#if defined(P_LORA_TX_LED)
+  void onBeforeTransmit() override {
+    digitalWrite(P_LORA_TX_LED, LOW);   // turn TX LED on
+  }
+  void onAfterTransmit() override {
+    digitalWrite(P_LORA_TX_LED, HIGH);   // turn TX LED off
+  }
+#endif
+
+  uint16_t getBattMilliVolts() override {
+    int adcvalue = 0;
+    analogReadResolution(12);
+    analogReference(AR_INTERNAL_3_0);
+    pinMode(PIN_BAT_CTL, OUTPUT);          // battery adc can be read only ctrl pin 6 set to high
+    digitalWrite(PIN_BAT_CTL, 1);
+
+    delay(10);
+    adcvalue = analogRead(PIN_VBAT_READ);
+    digitalWrite(6, 0);
+
+    return (uint16_t)((float)adcvalue * MV_LSB * 4.9);
+  }
+
+  const char* getManufacturerName() const override {
+    return "Heltec T114";
+  }
+
+  void powerOff() override {
+#ifdef LED_PIN
+    digitalWrite(LED_PIN, HIGH);
+#endif
+#if ENV_INCLUDE_GPS == 1
+    pinMode(GPS_EN, OUTPUT);
+    digitalWrite(GPS_EN, LOW);
+#endif
+    sd_power_system_off();
+  }
+};