move bat voltage check to startup

src/main.cpp

@@ -15,10 +15,22 @@ esp_adc_cal_characteristics_t *adc_chars;
 char DEVEUI[16];
 
 float getBatVoltage();
+void sleep();
+float batVoltage;
 
 void setup()
 {
   (String(ESP.getEfuseMac(), HEX) + "0000").toCharArray(DEVEUI, 17);
+  batVoltage = getBatVoltage();
+
+    if(BAT_MIN_VOLTAGE > batVoltage)
+  {
+#ifdef SERIAL_OUTPUT
+    Serial.println("Battery voltage too low, going to sleep again");
+    Serial.flush();
+#endif
+    sleep();
+  } 
 
   pinMode(Vext, OUTPUT);
   digitalWrite(Vext, LOW); // enable power to DS18B20
@@ -43,7 +55,7 @@ void setup()
   uint8_t txBuffer[14];
   txBuffer[0] = (rawTemp >> 8) & 0xFF;
   txBuffer[1] = rawTemp & 0xFF;
-  txBuffer[2] = (getBatVoltage() * 100) - 200;
+  txBuffer[2] = (batVoltage * 100) - 200;
 
 #ifdef SERIAL_OUTPUT
   Serial.print("Raw Temperature: ");
@@ -56,25 +68,12 @@ void setup()
 
 #ifdef SERIAL_OUTPUT
   Serial.print("Battery voltage: ");
-  Serial.println(getBatVoltage());
+  Serial.println(batVoltage);
   Serial.println("Going to sleep");
   Serial.flush();
 #endif
 
-
-  if(BAT_MIN_VOLTAGE < getBatVoltage())
-  {
-    uint64_t sleepTime = SLEEP_TIME * uS_TO_S_FACTOR;
-    esp_sleep_enable_timer_wakeup(sleepTime);
-  } 
-#ifdef SERIAL_OUTPUT
-  else
-  {
-    Serial.println("Battery voltage too low, going to permanent deep sleep");
-  }
-#endif
-
-  esp_deep_sleep_start();
+  sleep();
 }
 
 float getBatVoltage() {
@@ -86,6 +85,12 @@ float getBatVoltage() {
   return adcVal / 4095.0 * BAT_FACTOR;
 }
 
+void sleep() {
+  uint64_t sleepTime = SLEEP_TIME * uS_TO_S_FACTOR;
+  esp_sleep_enable_timer_wakeup(sleepTime);
+  esp_deep_sleep_start();
+}
+
 void loop()
 {
 }
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