Auto-Refreshing Weather Monitor, a ESP32 project

This project turns an Adafruit MagTag into a wall-mounted indoor weather display that automatically updates every minute. The e-ink screen shows current temperature in Fahrenheit and humidity percentage in large, easy-to-read text, making it perfect for a bedroom, office, or living room.

The guide includes a complete parts list, wiring diagram, and ready-to-upload firmware. Assembly is straightforward—use the MagTag as supplied, place it indoors, and power it on. The display refreshes automatically and uses minimal power thanks to the e-ink technology, so it can run for weeks on battery or indefinitely when plugged in.

Wiring diagram

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Assemble it in 3 steps

1. Use the MagTag as supplied

This project uses only the AdaBox 017 MagTag’s built-in 2.9-inch e-ink screen and built-in SHTC3 temperature/humidity sensor. No breadboard or jumper wiring is required.

Keep the sensor openings and the board clear of your hands while taking a reading so body heat does not influence it.
Do not connect external 5 V signals to the MagTag GPIO headers; its GPIO logic is 3.3 V.

2. Place it for an indoor reading

Set the MagTag upright in a shaded, ventilated indoor location, away from windows, radiators, direct sun, and air-conditioning outlets. Give it several minutes to settle after moving it.

The monitor is configured as an indoor temperature and humidity display; it does not use internet weather data.
Do not enclose the board in an airtight case, because trapped heat will make the temperature reading inaccurate.

3. Power the MagTag

Connect a USB-C cable to the MagTag for power while using the monitor. The e-ink screen retains its last image if power is removed, but the sensor cannot take new readings without power.

After deployment, the display draws immediately, then checks the sensor every minute.
Use a known-good USB power source and cable.

Deploy the firmware

main.cppOpen in Schematik

#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);
  }
}