warn if battery < 2.6V

the-cup.ino

@@ -19,6 +19,8 @@
 #include <MFRC522DriverPinSimple.h>
 #include <MFRC522Debug.h>
 
+#include "Adafruit_MAX1704X.h"
+
 #define SS_PIN SDA
 #define RC522_POWER_PIN 1
 #define SLEEP_DURATION 1
@@ -31,6 +33,8 @@ MFRC522 reader{driver_1};   // Create MFRC522 instance.
 
 RTC_DATA_ATTR int nbCycles = 0;
 
+Adafruit_MAX17048 lipo;
+
 const char *rootCACertificate = R"string_literal(
 -----BEGIN CERTIFICATE-----
 MIIFazCCA1OgAwIBAgIRAIIQz7DSQONZRGPgu2OCiwAwDQYJKoZIhvcNAQELBQAw
@@ -76,6 +80,8 @@ void setup() {
     Serial.println(nbCycles++);
   #endif
 
+  measureBattery();
+
   pinMode(RC522_POWER_PIN, OUTPUT);
   digitalWrite(RC522_POWER_PIN, HIGH);
   reader.PCD_Init(); // Init each MFRC522 card.
@@ -97,6 +103,15 @@ void loop() {
   }
 }
 
+void measureBattery() {
+  if (nbCycles % 10) {
+    lipo.begin();
+    if (lipo.cellVoltage() < 2.6) {
+      displayError();
+    }
+  }
+}
+
 void readCard(char reader_uid[]) {
   reader.PICC_HaltA();
   reader.PCD_StopCrypto1();