Create Arduino_PiCowbell_Doubler_Battery_Monitor.ino

PiCowbell_Doubler/Arduino_PiCowbell_Doubler_Battery_Monitor/Arduino_PiCowbell_Doubler_Battery_Monitor/Arduino_PiCowbell_Doubler_Battery_Monitor.ino

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+// SPDX-FileCopyrightText: 2024 Limor Fried for Adafruit Industries
+//
+// SPDX-License-Identifier: MIT
+
+#define LED    LED_BUILTIN
+
+void setup() {
+  Serial.begin(115200);
+  // while (!Serial)  delay(1);  // wait for serial port
+  pinMode(LED, OUTPUT);
+  delay (100);
+  Serial.println("PiCowbell Doubler Battery Monitor");
+
+}
+
+void loop() {
+  digitalWrite(LED, HIGH);
+  // get the on-board voltage
+  float vsys = analogRead(A3) * 3 * 3.3 / 1023.0;
+  Serial.printf("Vsys: %0.1f V", vsys);
+  Serial.println();
+
+  digitalWrite(LED, LOW);
+  delay(5000);
+}