From 293415fa50cda10e8659830a87aa5652be2b0f7b Mon Sep 17 00:00:00 2001
From: dakkar <dakkar@thenautilus.net>
Date: Sun, 27 Mar 2022 12:10:31 +0100
Subject: battery voltage, move display around

---
 battery.h | 38 ++++++++++++++++++++++++++++++++++++++
 main.ino  | 43 ++++++++++++++++++++++++++-----------------
 2 files changed, 64 insertions(+), 17 deletions(-)
 create mode 100644 battery.h

diff --git a/battery.h b/battery.h
new file mode 100644
index 0000000..825a3ab
--- /dev/null
+++ b/battery.h
@@ -0,0 +1,38 @@
+#pragma once
+#include <Arduino.h>
+
+/*
+  code inspired by https://gist.github.com/jenschr/dfc765cb9404beb6333a8ea30d2e78a1
+ */
+
+class Battery {
+  uint8_t pin;
+public:
+  /*
+    the schematics at
+    https://github.com/Xinyuan-LilyGO/LilyGo-T5-Epaper-Series/tree/master/schematic
+    show a voltage divider connected to pin 35
+  */
+  Battery(uint8_t _pin=35) : pin(_pin) {};
+  float voltage() {
+    /*
+      Comment from the gist:
+
+      The ADC value is a 12-bit number, so the maximum value is 4095
+      (counting from 0).
+
+      To convert the ADC integer value to a real voltage you’ll need
+      to divide it by the maximum value of 4095, then double it (note
+      above that Adafruit halves the voltage), then multiply that by
+      the reference voltage of the ESP32 which is 3.3V and then
+      finally, multiply that again by the ADC Reference Voltage of
+      1100mV.
+
+      Comment from me: that assumes that ADC is linear, which is probably isn't
+
+      Also, the battery voltage is not a decent indicator of charge
+      level, but that's what I've got
+    */
+    return (float)(analogRead(pin)) / 4095*2*3.3*1.1;
+  }
+};
diff --git a/main.ino b/main.ino
index bde8892..ce9f981 100644
--- a/main.ino
+++ b/main.ino
@@ -12,12 +12,16 @@
 #include <GxIO/GxIO_SPI/GxIO_SPI.h>
 #include <GxIO/GxIO.h>
 
+#include "battery.h"
+
 GxIO_Class io(SPI, EPD_CS, EPD_DC, EPD_RSET);
 GxEPD_Class display(io, EPD_RSET, EPD_BUSY);
 SPIClass SDSPI(VSPI); // for sdcard
 
 SensirionI2CScd4x scd4x;
 
+Battery batt;
+
 uint16_t co2 = 0;
 float temperature = 0.0f;
 float humidity = 0.0f;
@@ -25,24 +29,29 @@ struct sps30_measurement m;
 
 void showThings(bool all=false) {
   display.fillScreen(GxEPD_WHITE);
-  display.setCursor(0,20);
 
-  display.print("Co2:");
-  display.println(co2);
-  display.print("T:");
-  display.print(temperature);
-  display.print(" H:");
-  display.println(humidity);
-
-  display.print("PM 1:");
-  display.print(m.mc_1p0);
-  display.print(" PM 2.5:");
-  display.println(m.mc_2p5);
-
-  display.print("PM 4:");
-  display.print(m.mc_4p0);
-  display.print(" PM 10:");
-  display.println(m.mc_10p0);
+  display.setCursor(0,20);
+  display.print("Co2 ");
+  display.print(co2);
+
+  display.setCursor(100,20);
+  display.print("t");
+  display.print(temperature,1);
+
+  display.setCursor(150,20);
+  display.print(" h");
+  display.print(humidity,0);
+  display.print("%");
+
+  display.setCursor(0,45);
+  display.println("   PM");
+  display.print(" 1.0 "); display.println(m.mc_1p0,1);
+  display.print(" 2.5 "); display.println(m.mc_2p5,1);
+  display.print(" 4.0 "); display.println(m.mc_4p0,1);
+  display.print("10.0 "); display.println(m.mc_10p0,1);
+
+  display.setCursor(100,45);
+  display.print("Batt "); display.print(batt.voltage());
 
   // "partial" update
   display.updateWindow(0, 0, GxEPD_WIDTH, GxEPD_HEIGHT, false);
-- 
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