Imagine being able to switch a fan, heater, door lock, or remote system from up to 21 kilometers (13 miles) away—completely off-grid, without Wi-Fi, and without a SIM card. In this tutorial, you’ll learn how to build a secure long-range wireless relay controller using Heltec WiFi LoRa 32 V3 modules and the Robojax_HeltecLoRa32 library. This project enables encrypted LoRa communication to safely trigger relays over great distances.

Project Overview

This system consists of two LoRa32 boards:

• Transmitter (TX): A push button triggers an encrypted command ("ON" or "OFF") over LoRa.

• Receiver (RX): Listens for and decrypts the command, then controls a relay module connected to GPIO4 accordingly.

You have two transmitter code versions:

• Simple: Sends ON when the button is held down, OFF when released.

• Toggle: Alternates the state with each press.

Required Library

You must install the Robojax_HeltecLoRa32 library. Download it from the link below this article.

Install this ZIP library via Arduino IDE before uploading any code.

Wiring Instructions

Transmitter Wiring:

• User button connected to GPIO0

• Optional: OLED display uses default pins (SCL/SDA)

Receiver Wiring:

• Relay (or buzzer) control pin connected to GPIO4

• 5V Relay module powered via board's 5V and GND

Secure TX Code Explanation

In both TX sketches, encryption is enabled using the setSecurityKey() method from the Robojax library. For example:

const char *userKey = "hyhT676#h~_876s";
robojaxDevice.setSecurityKey(userKey);

In Relay_Secure_TX_Simple.ino, a HIGH signal on GPIO0 sends "ON", while a LOW sends "OFF":

if(digitalRead(0) == HIGH){
  robojaxDevice.sendSecureMessage("ON");
} else {
  robojaxDevice.sendSecureMessage("OFF");
}

In Relay_Secure_TX_Toggle.ino, each button press toggles between ON and OFF:

if(buttonPressed){
  status = !status;
  String message = status ? "ON" : "OFF";
  robojaxDevice.sendSecureMessage(message);
}

Secure RX Code Explanation

The receiver sketch uses the same encryption key and listens for secure messages:

robojaxDevice.setSecurityKey("hyhT676#h~_876s");
String message = robojaxDevice.receiveSecureMessage();

Then controls GPIO4 accordingly:

if(message == "ON"){
  digitalWrite(RELAY_CONTROL_PIN, HIGH);
} else if(message == "OFF"){
  digitalWrite(RELAY_CONTROL_PIN, LOW);
}

The OLED display shows the received state and "RX" label.

📚 Chapter Index

1. [00:00] Project Introduction and Range Demonstration

2. [00:08] Use Cases: Fan, Heater, Gate, Light

3. [00:20] Hardware Used

4. [00:40] Wiring Overview

5. [01:00] Installing Robojax Library

6. [01:20] TX Code (Simple Version)

7. [01:40] TX Code (Toggle Version)

8. [02:00] RX Code Explanation

9. [02:20] Live Demonstration

This tutorial provides a robust and secure way to wirelessly control devices over long distances. All code and the required library are available below this article. Watch the full video to follow along!