Thinknode_M2: better battery reading accuracy and no display on powerup fix

variants/thinknode_m2/ThinknodeM2Board.cpp

@@ -3,12 +3,13 @@
 
 
 void ThinknodeM2Board::begin() {
+    pinMode(PIN_VEXT_EN, OUTPUT); 
+    digitalWrite(PIN_VEXT_EN, !PIN_VEXT_EN_ACTIVE); // force power cycle
+    delay(20); // allow power rail to discharge
+    digitalWrite(PIN_VEXT_EN, PIN_VEXT_EN_ACTIVE); // turn backlight back on
+    delay(120); // give display time to bias on cold boot
     ESP32Board::begin();
-    pinMode(PIN_VEXT_EN, OUTPUT); // init display
-    digitalWrite(PIN_VEXT_EN, PIN_VEXT_EN_ACTIVE); // pin needs to be high
-    delay(10); 
-    digitalWrite(PIN_VEXT_EN, PIN_VEXT_EN_ACTIVE); // need to do this twice. do not know why..
-    pinMode(PIN_STATUS_LED, OUTPUT); // init power led    
+    pinMode(PIN_STATUS_LED, OUTPUT); // init power led
   }
 
   void ThinknodeM2Board::enterDeepSleep(uint32_t secs, int pin_wake_btn) {
@@ -19,14 +20,21 @@ void ThinknodeM2Board::begin() {
     enterDeepSleep(0);
   }
 
-  uint16_t ThinknodeM2Board::getBattMilliVolts()  {
+ uint16_t ThinknodeM2Board::getBattMilliVolts() {
     analogReadResolution(12);
-    delay(10);
-    float volts = (analogRead(PIN_VBAT_READ) * ADC_MULTIPLIER * AREF_VOLTAGE) / 4096;
-    analogReadResolution(10);
-    return volts * 1000;
-  }
+    analogSetPinAttenuation(PIN_VBAT_READ, ADC_11db);
+
+    uint32_t mv = 0;
+      for (int i = 0; i < 8; ++i) {
+        mv += analogReadMilliVolts(PIN_VBAT_READ);
+        delayMicroseconds(200);
+      }
+    mv /= 8;
+
+    analogReadResolution(10);  
+    return static_cast<uint16_t>(mv * ADC_MULTIPLIER );
+}
 
   const char* ThinknodeM2Board::getManufacturerName() const {
     return "Elecrow ThinkNode M2";
-  }
+  }

variants/thinknode_m2/variant.h

@@ -1,15 +1,12 @@
 #define I2C_SCL 15
 #define I2C_SDA 16
-#define  PIN_VBAT_READ    17
+#define PIN_VBAT_READ    17
 #define AREF_VOLTAGE            (3.0)
-#define ADC_MULTIPLIER (1.548F)
+#define ADC_MULTIPLIER (1.509F)
 #define PIN_BUZZER 5
 #define PIN_VEXT_EN_ACTIVE HIGH
 #define PIN_VEXT_EN 46
 #define PIN_USER_BTN 47
 #define PIN_LED 6
 #define PIN_STATUS_LED 6
 #define PIN_PWRBTN 4
-
-
-