ESP32 Request Repeater With Sleep

Posted: Tuesday, February 18, 2025 at 06:46 PM | Categories: Arduino, ESP32, Internet of Things (IoT)

In my previous post I described how to put an ESP device to sleep (allowing it to wake up later). I used a sample sketch I created, ESP32 Request Repeater (HTTP), to show how it works.

The sample sketch sends a HTTP to a remote host, then puts the device to sleep (deep sleep) with instructions to wake up two minutes later to do it again. I realized then I would probably make a TLS (HTTPS) version of the sketch and publish it as well. Well, I published it, and this post highlights the differences between it and the HTTP version.

Both versions (HTTP and HTTPS) of the sketch:

1. Tells you how many times it's woken and made (or tried to make) a request
2. Waits for 30 seconds so you can upload sketch updates to the device
3. Connects to the Wi-Fi network
4. Sends the request (this version sends the request using TLS (HTTPS))
5. Puts the device to sleep for SLEEP_DURATION_MINUTES

So it's the exact same approach except for the more secure nature of the request.

Initialization

The initialization section of the code has only a few changes, mostly additions:

#include <WiFiClientSecure.h>

#include "cert.h"

HTTPClient https;
WiFiClientSecure* client = new WiFiClientSecure;

The code has the following changes:

• Added the WiFiClientSecure library which implements a client object the sketch uses to create an HTTPS request.
• Added the Certificate Authority (CA) certificate file cert.h required to enable secure communications with the remote host using TLS (HTTPS). I wrote more about this in ESP32 Connect Using HTTPS
• Changed the HTTPClient variable from http to https
• Created a new client object using WiFiClientSecure.

Beyond those simple changes, the remaining changes are in the callRemoteHost() function described below.

Sending the Request

In the sketch, I enhanced the callRemoteHost() function to use the client object to manage the secure connection to the remote host:

void callRemoteHost() {
  client->setCACert(caCert);
  Serial.printf("Connecting to %s\n", REMOTE_HOST);
  if (https.begin(*client, REMOTE_HOST)) {
    // start connection to host as a GET request
    int httpCode = https.GET();
    if (httpCode > 0) {  // httpCode is negative on error
      Serial.printf("Response: %d\n", httpCode);
      if (httpCode == HTTP_CODE_OK) {
        String payload = https.getString();
        Serial.println(payload);
      }
    } else {
      Serial.printf("GET failed, error: %s\n", https.errorToString(httpCode).c_str());
    }
    // close the connection
    https.end();
  }
}

The differences from the HTTP version are:

• Assigning the CA cert to the client object
• Passing the client object (well, a pointer to the client object anyway) when begining the request

Otherwise it's essentially the same code.

One other difference is that the sketch checks the status of the call to begin and only tries to send the request when that succeeds. I don't know where I pulled that code from, I imagine it would work as well without it.

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