Implement EPD deep sleep; Render battery voltage on screen

NightscoutEInkClient.ino

@@ -3,6 +3,7 @@
 #include <WiFi.h>
 #include <HTTPClient.h>
 #include <time.h>
+#include "esp_sleep.h"
 
 //PIN LAYOUTS
   #define SRAM_CS     32
@@ -10,8 +11,9 @@
   #define EPD_DC      33  
   #define EPD_RESET   -1 // can set to -1 and share with microcontroller Reset!
   #define EPD_BUSY    27 // can set to -1 to not use a pin (will wait a fixed delay) 
-
-
+  #define EPD_ENABLE  12
+  #define BATTERY_PIN A13
+  
 ThinkInk_290_Tricolor_Z10 display(EPD_DC, EPD_RESET, EPD_CS, SRAM_CS, EPD_BUSY);
 
 #define COLOR0 EPD_WHITE
@@ -37,6 +39,10 @@ void setup() {
   while (!Serial) { delay(10); }
   Serial.println("Nightscout CGM BS Monitor starting...");
 
+  //turn EPD on
+  pinMode(EPD_ENABLE, OUTPUT);
+  digitalWrite(EPD_ENABLE, HIGH);
+  
   ConnectToWifi();
   String nightscoutResponse = httpGETRequest(nightscoutUrl);
   Serial.println(nightscoutResponse);
@@ -57,6 +63,7 @@ void setup() {
 
   RenderGraph(array);
   RenderRightPane(array[0]);
+  RenderBatteryPercentage();
 
   display.display();
 
@@ -101,6 +108,7 @@ void SleepWithTimeSync(int lastReadingInSeconds) {
     secondsToSleep = secondsToSleep + 7;
     esp_sleep_enable_timer_wakeup(secondsToSleep * uS_TO_S_FACTOR);
     Serial.flush(); 
+    TurnOffEPD();
     esp_deep_sleep_start();
   }
   else {
@@ -109,9 +117,38 @@ void SleepWithTimeSync(int lastReadingInSeconds) {
   
 }
 
+void RenderBatteryPercentage() {
+  int batteryPinInput = analogRead(BATTERY_PIN);
+  Serial.printf("raw adc value %d", batteryPinInput);
+  //Vin = 3.3(read/4098)
+  float batteryVoltage = 3.3 * (float(batteryPinInput) / 4098.0);
+  //ESP32 A13 returns half the voltage, so double this reading
+  batteryVoltage = batteryVoltage * 2.0;
+  Serial.print("calc. voltage ");
+  Serial.println(batteryVoltage);
+
+  //Render on screen
+  display.setCursor(245, 110);
+  display.setTextSize(2);
+  if(batteryVoltage < 3.6)
+    display.setTextColor(COLOR2);
+  else
+    display.setTextColor(COLOR1);
+  display.print(batteryVoltage);
+  display.print("v");
+}
+
+void TurnOffEPD() {
+  digitalWrite(EPD_ENABLE, LOW);
+  delay(1000);
+  gpio_hold_en(GPIO_NUM_12);
+  gpio_deep_sleep_hold_en();
+}
+
 void SleepFiveMins() {
   esp_sleep_enable_timer_wakeup(285 * uS_TO_S_FACTOR);
   Serial.flush(); 
+  TurnOffEPD();
   esp_deep_sleep_start();
 }