Connecting to Wi-Fi with ESP32

Joining Wi-Fi

#include <WiFi.h>
#include "secrets.h"     // defines WIFI_SSID, WIFI_PASS, API_TOKEN (not committed to Git)

void setup() {
  Serial.begin(115200);
  WiFi.mode(WIFI_STA);
  WiFi.begin(WIFI_SSID, WIFI_PASS);
  while (WiFi.status() != WL_CONNECTED) { delay(500); Serial.print("."); }
  Serial.println(WiFi.localIP());
}

Keep credentials in a secrets.h file listed in .gitignore. For devices you give to others, use a provisioning method (such as a setup access point or Bluetooth) so users enter their own Wi-Fi details.

Sending readings to an API

#include <HTTPClient.h>
#include <WiFiClientSecure.h>

void sendReading(float tempC, float humidity) {
  WiFiClientSecure client;
  client.setCACert(ROOT_CA_PEM);              // verify the server's certificate
  HTTPClient http;
  http.begin(client, "https://api.example.com/v1/readings");
  http.addHeader("Content-Type", "application/json");
  http.addHeader("Authorization", String("Bearer ") + API_TOKEN);
  String body = "{\"device\":\"greenhouse-1\",\"temp_c\":" + String(tempC, 1) +
                ",\"humidity\":" + String(humidity, 1) + "}";
  int code = http.POST(body);
  Serial.printf("POST -> %d\n", code);
  http.end();
}

• Use HTTPS and verify certificates; avoid setInsecure() outside quick experiments.
• Give each device its own token with limited permissions so one stolen device does not compromise others.
• Handle failures: retry with backoff, and buffer readings if the network is down.

The receiving side

A small Flask endpoint (see API Design & REST) validates the token, checks the payload, stores readings and rate-limits each device.

Exercise

Send your weather station's readings every minute to a Flask API over HTTPS with a per-device token; store them in PostgreSQL and show the latest reading on a web page.

Check yourself

• Why keep Wi-Fi credentials out of the sketch file?
• Why give each device its own token?
• What should a device do when the network is down?