EXT_PWR_DETECT pin to detect external power source for boards without the power management chip

src/Power.cpp

@@ -160,8 +160,18 @@ class AnalogBatteryLevel : public HasBatteryLevel
 
     /// If we see a battery voltage higher than physics allows - assume charger is pumping
     /// in power
+    /// On some boards we don't have the power management chip (like AXPxxxx)
+    /// so we use EXT_PWR_DETECT GPIO pin to detect external power source
     virtual bool isVbusIn() override
     {
+#ifdef EXT_PWR_DETECT
+    // if external powered that pin will be pulled up
+    if (digitalRead(EXT_PWR_DETECT) == HIGH) {
+        return true;
+    }
+    // if it's not HIGH - check the battery
+#endif
+
         return getBattVoltage() > chargingVolt;
     }
 

src/PowerFSM.cpp

@@ -26,6 +26,9 @@ static bool isPowered()
         1) If we're powered up and there's no battery, we must be getting power externally. (because we'd be dead otherwise)
 
         2) If we detect USB power from the power management chip, we must be getting power externally.
+
+        3) On some boards we don't have the power management chip (like AXPxxxx) so we use EXT_PWR_DETECT GPIO pin to detect external power source
+            (see `isVbusIn()` in `Power.cpp`)
     */
     return !isPowerSavingMode && powerStatus && (!powerStatus->getHasBattery() || powerStatus->getHasUSB());
 }

variants/diy/v1/variant.h

@@ -12,6 +12,7 @@
 #define BUTTON_PIN 39       // The middle button GPIO on the T-Beam
 #define BATTERY_PIN 35      // A battery voltage measurement pin, voltage divider connected here to measure battery voltage
 #define ADC_MULTIPLIER 1.85 // (R1 = 470k, R2 = 680k)
+#define EXT_PWR_DETECT 4    // Pin to detect connected external power source for LILYGO® TTGO T-Energy T18 and other DIY boards
 #define EXT_NOTIFY_OUT 12   // Overridden default pin to use for Ext Notify Module (#975).
 #define LED_PIN 2           // add status LED (compatible with core-pcb and DIY targets)