Hello, forum members!
I’m kind of new to the ESP32 field, so I might be making a simple mistake, but I haven’t found any solutions yet. Here’s the situation: I have 3 ESP32 devices, where:
- 1 is a master and 2 are slaves.
- When a button is pressed on the master (it has 2 buttons), it makes either Slave 1 or Slave 2 activate an LED, generate a random number between 0-100, and send it to an MQTT server.
Everything works fine, but the problem is with the serial print on the master:
When I try to print the random number to the serial monitor, it returns a special character like shown here:
makefile
09:35:46.444 -> Slave 1 sent: �
09:35:48.714 -> Slave 2 sent: �
I’m not sure why it’s returning this value in the Serial.println. I’ve already tried:
- Changing the baud rate from 115200 to 9600, but it didn’t work.
- Converting the value to a string manually on the slave side, but that didn’t help either.
Does anyone know what might be causing this?
Master code:
#include <Arduino.h>
#include <stdio.h>
#include <string.h>
#include <HardwareSerial.h>
HardwareSerial SerialPort(2);
int slave_1_id = 1;
int slave_2_id = 2;
const int BUTTON_PIN_01 = 12;
const int BUTTON_PIN_02 = 13;
const int Enable = 15;
void setup() {
Serial.begin(115200);
SerialPort.begin(115200, SERIAL_8N1, 16, 17);
pinMode(Enable, OUTPUT);
digitalWrite(Enable, LOW);
pinMode(BUTTON_PIN_01, INPUT_PULLUP);
pinMode(BUTTON_PIN_02, INPUT_PULLUP);
}
void loop() {
/* Master Program */
if(digitalRead(BUTTON_PIN_01) == 0){
digitalWrite(Enable, HIGH);
SerialPort.print(slave_1_id);
SerialPort.print("ON");
SerialPort.flush();
digitalWrite(Enable, LOW);
delay(500); // Delay to wait for response
// Wait for response from slave 1
if(SerialPort.available()){
String response = SerialPort.readStringUntil('\n'); // Read until newline
Serial.println("Slave 1 sent: " + response); // Print the random number sent by the slave
}
}
if(digitalRead(BUTTON_PIN_02) == 0){
digitalWrite(Enable, HIGH);
SerialPort.print(slave_2_id);
SerialPort.print("ON");
SerialPort.flush();
digitalWrite(Enable, LOW);
delay(500); // Delay to wait for response
// Wait for response from slave 2
if(SerialPort.available()){
String response = SerialPort.readStringUntil('\n'); // Read until newline
Serial.println("Slave 2 sent: " + response); // Print the random number sent by the slave
}
}
delay(200);
}
Slave code (both of them are equal, just changing the slave id
#include <WiFi.h>
#include <PubSubClient.h>
#include <HardwareSerial.h>
// Slave definitions
HardwareSerial SerialPort(2);
const int Enable = 15;
const int SlaveNumber = 1; // Slave ID for master's read
int Slave;
const int LED = 4;
// WiFi definitions
const char* ssid = "YOUR_WIFI_SSID";
const char* password = "YOUR_WIFI_PASSWORD";
// MQTT definitions
const char* server = "YOUR_MQTT_SERVER_ADDRESS";
const int porta = 1883;
const char* topic_base = "YOUR_TOPIC_BASE";
WiFiClient ethClient;
PubSubClient mqttClient(ethClient);
void connectToWiFi() {
WiFi.begin(ssid, password);
while (WiFi.status() != WL_CONNECTED) {
delay(500);
Serial.println("Connecting to WiFi...");
}
Serial.println("Connected to WiFi");
}
void connectToMQTT() {
mqttClient.setServer(server, porta);
while (!mqttClient.connected()) {
Serial.println("Connecting to MQTT...");
if (mqttClient.connect("slave_device")) {
Serial.println("Connected to MQTT");
} else {
delay(1000);
}
}
}
void setup() {
Serial.begin(115200);
SerialPort.begin(115200, SERIAL_8N1, 16, 17);
SerialPort.setTimeout(250);
pinMode(Enable, OUTPUT);
pinMode(LED, OUTPUT);
digitalWrite(Enable, LOW);
digitalWrite(LED, LOW);
randomSeed(analogRead(0)); // Initialize random number generator
// Connect to WiFi and MQTT
connectToWiFi();
connectToMQTT();
}
void loop() {
digitalWrite(Enable, LOW);
if (SerialPort.available()) {
Slave = SerialPort.parseInt();
Serial.println(Slave);
if (Slave == SlaveNumber) {
String command = SerialPort.readString();
Serial.println(command);
if (command == "ON") {
digitalWrite(LED, HIGH);
// Generate and print a random number between 0 and 100
int randomNumber = random(0, 101);
Serial.print("Random number: ");
Serial.println(randomNumber);
// Send the random number via MQTT
char message[100];
sprintf(message, "Slave %d sent number: %d", SlaveNumber, randomNumber);
// Publish to MQTT topic corresponding to the slave
char topic[50];
sprintf(topic, "%s%d/number", topic_base, SlaveNumber); // E.g., YOUR_TOPIC_BASE1/number
bool enviado = mqttClient.publish(topic, message);
if (enviado) {
Serial.print("Number sent via MQTT: ");
Serial.println(message);
} else {
Serial.println("Failed to send number via MQTT.");
}
digitalWrite(Enable, HIGH);
SerialPort.println(randomNumber); // Send the number back to the master as a string
digitalWrite(Enable, LOW);
delay(500);
digitalWrite(LED, LOW);
}
}
Serial.println("loop");
}
// Maintain MQTT connection
if (!mqttClient.connected()) {
while (!mqttClient.connected()) {
Serial.println("Reconnecting to MQTT...");
if (mqttClient.connect("device")) {
Serial.println("Reconnected");
} else {
delay(5000);
}
}
}
}