Auto-Refreshing Weather Monitor

#include <Arduino.h>
#include <Adafruit_MagTag.h>
#include <math.h>


// Forward declarations
void drawMonitor(float temperatureC, float humidity);
void updateWeather(bool forceRefresh);

Adafruit_MagTag magtag;

constexpr uint32_t SENSOR_INTERVAL_MS = 60000UL;       // Read the sensor once per minute.
constexpr uint32_t HEARTBEAT_REFRESH_MS = 300000UL;    // Refresh at least every 5 minutes.

uint32_t lastSampleMs = 0;
uint32_t lastRefreshMs = 0;
int lastTemperatureTenths = INT16_MIN;
int lastHumidityTenths = INT16_MIN;

void drawMonitor(float temperatureC, float humidity) {
  const float temperatureF = temperatureC * 9.0f / 5.0f + 32.0f;

  magtag.setTextWrap(false);
  magtag.setTextColor(EPD_BLACK);
  magtag.fillScreen(EPD_WHITE);

  magtag.setTextSize(2);
  magtag.setCursor(12, 18);
  magtag.print("INDOOR WEATHER");
  magtag.drawFastHLine(12, 43, 272, EPD_BLACK);

  magtag.setTextSize(2);
  magtag.setCursor(18, 78);
  magtag.print("Temperature");
  magtag.setTextSize(4);
  magtag.setCursor(18, 125);
  magtag.print(temperatureF, 1);
  magtag.print(" F");

  magtag.setTextSize(2);
  magtag.setCursor(18, 177);
  magtag.print("Humidity");
  magtag.setTextSize(4);
  magtag.setCursor(18, 224);
  magtag.print(humidity, 1);
  magtag.print(" %");

  magtag.setTextSize(1);
  magtag.setCursor(12, 282);
  magtag.print("Updates automatically every minute");

  // This call transfers the new framebuffer to the e-ink panel. Without it,
  // drawing calls alone do not visibly update the MagTag display.
  magtag.refresh();
}

void updateWeather(bool forceRefresh) {
  const float temperatureC = magtag.peripherals.temperaturesensor.readTemperature();
  const float humidity = magtag.peripherals.humiditysensor.readHumidity();

  if (isnan(temperatureC) || isnan(humidity)) {
    return; // Retain the last valid screen if an I2C sensor read fails.
  }

  const int temperatureTenths = (int)lroundf(temperatureC * 10.0f);
  const int humidityTenths = (int)lroundf(humidity * 10.0f);
  const bool readingChanged = temperatureTenths != lastTemperatureTenths ||
                              humidityTenths != lastHumidityTenths;

  if (forceRefresh || readingChanged) {
    drawMonitor(temperatureC, humidity);
    lastTemperatureTenths = temperatureTenths;
    lastHumidityTenths = humidityTenths;
    lastRefreshMs = millis();
  }
}

void setup() {
  magtag.begin();
  updateWeather(true); // Show an initial, explicit refresh immediately after boot.
  lastSampleMs = millis();
}

void loop() {
  const uint32_t now = millis();

  if (now - lastSampleMs >= SENSOR_INTERVAL_MS) {
    lastSampleMs = now;
    const bool heartbeatDue = now - lastRefreshMs >= HEARTBEAT_REFRESH_MS;
    updateWeather(heartbeatDue);
  }
}