read voltage from Hazzah32 battery connector

wiflash_esp32/wiflash_esp32.ino

@@ -83,6 +83,9 @@ NeoPixelBus<NeoGrbwFeature, Neo800KbpsMethod> *strip;
 ESPAsyncE131 *e131 = new ESPAsyncE131();
 Preferences prefs;
 
+//// static hardware
+const uint8_t battery_sense = A13;  //Hazzah32 battery connected to A13
+
 //// Global button variables
 bool pressed = false;    // track button state
 uint32_t change_time;    // time of button press (ms)
@@ -161,6 +164,20 @@ bool loadConfig() {
 }
 
 
+/*
+   Read the battery level
+*/
+float batteryVoltage() {
+  float v;
+  v = analogRead(battery_sense);  // 12bit reading
+  v /= 4095.0f;                   // percent of range
+  v *= 2.0f;                      // doubled
+  v *= 3.3f;                      // percent of referance voltage
+  v *= 1.1f;                      // multiply by ADC resolution (V)
+  return v;
+}
+
+
 /*
    Arduino powerup
 */
@@ -189,6 +206,9 @@ void setup() {
 
 
   //// start fixtures hardware:
+  // battery monitor
+  pinMode(battery_sense, INPUT);
+
   // button
   if (config.button_enable) {
     Serial.println("Initializing OSC button");