ttgo-t5-v2.3_battery.ino

#include <GxEPD2_BW.h>

#include <Fonts/FreeMonoBold9pt7b.h>

#define EPD_CS SS

GxEPD2_BW<GxEPD2_213_B73, GxEPD2_213_B73::HEIGHT> display(GxEPD2_213_B73(/*CS=5*/ SS, /*DC=*/ 17, /*RST=*/ 16, /*BUSY=*/ 4)); // GDEH0213B73

#define BAT 35

void setup() {
  pinMode(BAT, INPUT);

  //float volt = (long)analogRead(BAT) * 3300. / 4096. * 2. ;
  float volt = (long)analogRead(BAT) * 3600. / 4095. * 2. ;

  display.init(115200);
  display.firstPage();
  do
  {
    display.setFont(&FreeMonoBold9pt7b);
    display.setTextColor(GxEPD_BLACK);
    display.setFullWindow();
    display.setCursor(0, 10);
    display.print(String((long)volt) + " mV");
  }
  while (display.nextPage());

  display.hibernate();
}

void loop(void) {
}