This is the canonical 'first real IoT project', temperature, humidity, pressure, all WiFi-connected, all visible on your phone. We use it as the starting template for our BlitzAgroTech smart weather stations deployed across Zimbabwean farms.
Parts and prep
- ESP32 DevKit-C (or any ESP32 board with WiFi)
- DHT22, temperature + humidity
- BMP280, barometric pressure + temperature (I2C)
- Breadboard, jumper wires, 10 kΩ resistor
- An MQTT broker, we recommend a free HiveMQ Cloud account (1 GB free, plenty for a personal weather station)
Wiring
ESP32 → DHT22:
3V3 → VCC
GPIO 4 → DATA (with 10 kΩ pull-up to 3V3)
GND → GND
ESP32 → BMP280 (I2C):
3V3 → VCC
GND → GND
GPIO 21 → SDA
GPIO 22 → SCL
Arduino IDE setup for ESP32
Arduino IDE → File → Preferences → Additional Boards URLs:
https://raw.githubusercontent.com/espressif/arduino-esp32/gh-pages/package_esp32_index.json
Then Tools → Board → Boards Manager → search 'esp32' → install Espressif esp32. Also install these libraries: 'DHT sensor library', 'Adafruit BMP280', 'PubSubClient' (for MQTT).
The firmware
Replace WIFI_SSID, WIFI_PASS, MQTT_HOST, MQTT_USER, MQTT_PASS with your values before uploading. Open Serial Monitor at 115200 baud to watch it connect and publish.
#include <WiFi.h>
#include <PubSubClient.h>
#include <DHT.h>
#include <Adafruit_BMP280.h>
#define WIFI_SSID "YourWiFi"
#define WIFI_PASS "YourPass"
#define MQTT_HOST "xxxxx.s1.eu.hivemq.cloud"
#define MQTT_PORT 8883
#define MQTT_USER "user"
#define MQTT_PASS "pass"
#define DHTPIN 4
#define DHTTYPE DHT22
DHT dht(DHTPIN, DHTTYPE);
Adafruit_BMP280 bmp;
WiFiClient espClient;
PubSubClient client(espClient);
void setup() {
Serial.begin(115200);
dht.begin();
bmp.begin(0x76);
WiFi.begin(WIFI_SSID, WIFI_PASS);
while (WiFi.status() != WL_CONNECTED) { delay(500); Serial.print("."); }
client.setServer(MQTT_HOST, MQTT_PORT);
}
void loop() {
if (!client.connected()) {
client.connect("blitztech-weather", MQTT_USER, MQTT_PASS);
}
client.loop();
float h = dht.readHumidity();
float t = dht.readTemperature();
float p = bmp.readPressure() / 100.0;
char buf[128];
snprintf(buf, sizeof(buf),
"{\"temp\":%.1f,\"humidity\":%.1f,\"pressure\":%.1f}", t, h, p);
client.publish("blitztech/weather", buf);
Serial.println(buf);
delay(30000);
}View on your phone
Install the free 'IoT MQTT Panel' app on your phone (Android/iOS). Add a connection to your HiveMQ broker with the same credentials. Subscribe to 'blitztech/weather' and add Number widgets bound to the temp / humidity / pressure JSON keys. Refresh every 30 seconds. That's a deployed IoT device.
Where this goes next
- Add a solar panel + LiPo battery for outdoor deployment.
- Add a soil-moisture sensor and run from low-power deep-sleep on a 6-hour cadence to monitor a Zimbabwean field for a year on one battery charge.
- This is the basic platform for BlitzAgroTech smart weather stations. Contact us if you want to deploy this at agricultural scale.