initial t-echo card support

variants/lilygo_techo_card/TechoCardBoard.h

@@ -0,0 +1,34 @@
+#pragma once
+
+#include <MeshCore.h>
+#include <Arduino.h>
+#include <helpers/NRF52Board.h>
+#include <Adafruit_Neopixel.h>
+
+// built-ins
+#define VBAT_MV_PER_LSB   (0.73242188F)   // 3.0V ADC range and 12-bit ADC resolution = 3000mV/4096
+
+#define VBAT_DIVIDER      (0.5F)          // Even voltage divider on VBAT
+#define VBAT_DIVIDER_COMP (2.0F)          // Compensation factor for the VBAT divider
+
+#define PIN_VBAT_READ     (2)
+#define REAL_VBAT_MV_PER_LSB (VBAT_DIVIDER_COMP * VBAT_MV_PER_LSB)
+
+class TechoCardBoard : public NRF52BoardDCDC {
+public:
+  TechoCardBoard() : NRF52Board("TECHO_OTA") {}
+  void begin();
+  uint16_t getBattMilliVolts() override;
+  void onBeforeTransmit(void) override;
+  void onAfterTransmit(void) override;
+
+
+  const char* getManufacturerName() const override {
+    return "LilyGo T-Echo Card";
+  }
+
+  void powerOff() override;
+
+  void turnOffLeds();
+  
+};