Transmitting data wirelessly using HC-12

Using Arduino Project Guidance
1

Hello, I'm currently working on a project that involves two stations: a transmitter and a receiver. Please keep in mind that I'm a beginner.

On the transmitter side, I'm using an ESP32, HC-12 433MHz module, GPS NEO-6M module, BME280 sensor, and a microSD card reader. The goal is to send data from the GPS and BME280 to the receiver twice a second and output it to the serial monitor.

I managed to create code for both stations that works as intended, but there are a few issues bothering me. Firstly, I haven't been able to figure out how to properly set the delay so that it sends the data twice a second. Secondly, when I disconnect the microSD card while the ESP32 is running, the interval between each attempt to send data becomes much longer. I resolved this by creating an if statement that disables writing to the microSD after I type a command in the serial monitor. But I'm still curious if there's a better way to handle this issue and what causes this behavior.

Additionally, I noticed that on the transmitter side, it's able to output the data with a delay set to 100ms four times a second, but the receiver only receives three lines of data.

Finally, I would appreciate it if you could review my code and suggest improvements to take a different approach or make it more readable.

Is someone able to solve these problems for me and send me the solution with explanation? If that's too much could someone please tell me where should I look for the answer?

Here's the code for the transmitter.

//tx
#include <Wire.h>
#include <SPI.h>
#include <SoftwareSerial.h>
#include <Arduino.h>
#include <Adafruit_Sensor.h>
#include <Adafruit_BME280.h>
#include <TinyGPSPlus.h>
#include <FS.h>
#include <SD.h>
#include <SPI.h>

#define RXD2 16 //(RX2)
#define TXD2 17 //(TX2)
#define SDA_PIN 21
#define SCL_PIN 22
#define pinSet 4 //set
#define SD_CS_PIN 5
#define HC12 Serial2 //Hardware serial 2 on the ESP32
static const int RXPin = 14, TXPin = 12;
static const uint32_t GPSBaud = 9600;

char serialZnak;
char HC12Znak;
String serialZprava = "";
String HC12Zprava = "";
boolean serialKonecZpravy = false;
boolean HC12KonecZpravy = false;
boolean communicationEnabled = true;
boolean sdEnabled = true; // Flag to control communication
unsigned long lastTransmissionTime = 0;

Adafruit_BME280 bme;
TinyGPSPlus gps;

SoftwareSerial ss(RXPin, TXPin);
File dataFile;
void setup()
{
  Serial.begin(9600);
  Wire.begin(SDA_PIN, SCL_PIN);
  if (!bme.begin(0x76, &Wire))
  {
    Serial.println("BME280 sensor not found. Check wiring!");
    while (1);
  }
  if (!SD.begin(SD_CS_PIN)) {
        Serial.println("SD card initialization failed");
        sdEnabled = false;
        return;
    }
  dataFile = SD.open("/data.csv", FILE_WRITE);
  if (!dataFile) {
    Serial.println("Error opening data.csv");
  } 
  else {
    // Check if file is empty
    if (dataFile.size() == 0) {
      // Write header to the file
      dataFile.println("Temperature;Humidity;Pressure;Latitude;Longitude;Time;Speed;Altitude;");
    }
    dataFile.close(); // Close the file after writing header
  }
  pinMode(pinSet, OUTPUT);
  digitalWrite(pinSet, HIGH);
  delay(80);
  HC12.begin(9600, SERIAL_8N1, RXD2, TXD2);
  ss.begin(GPSBaud);
}

void loop()
{
  unsigned long currentTime = millis();
  while (HC12.available())
  {
    HC12Znak = HC12.read();
    HC12Zprava += char(HC12Znak);
    if (HC12Znak == '\n')
    {
      HC12KonecZpravy = true;
    }
  }

  while (Serial.available())
  {
    serialZnak = Serial.read();
    serialZprava += char(serialZnak);
    if (serialZnak == '\n')
    {
      serialKonecZpravy = true;
    }
  }

  if (serialKonecZpravy)
  {
    if (serialZprava.startsWith("COM+ON"))
    {
      communicationEnabled = true;
      Serial.println("Communication enabled.");
      HC12.println("Communication enabled.");
    }
    else if (serialZprava.startsWith("COM+OFF"))
    {
      communicationEnabled = false;
      Serial.println("Communication disabled.");
      HC12.println("Communication disabled.");
    }
    else if (serialZprava.startsWith("COM+SD+ON"))
    {
      sdEnabled = true;
      Serial.println("SD enabled.");
      HC12.println("COM+OFF");
      
    }
    else if (serialZprava.startsWith("COM+SD+OFF"))
    {
      sdEnabled = false;
      Serial.println("SD disabled.");
      HC12.println("COM+OFF");
    }
    else if (serialZprava.startsWith("AT")) 
    {
      HC12.print(serialZprava);
      delay(100);
      digitalWrite(pinSet, LOW);
      delay(100);
      Serial.print(serialZprava);
      HC12.print(serialZprava);
      delay(500);
      digitalWrite(pinSet, HIGH);
      delay(100);
    }
    else
    {
      HC12.print(serialZprava);
    }

    serialZprava = "";
    serialKonecZpravy = false;
  }

  if (HC12KonecZpravy)
  {
    if (HC12Zprava.startsWith("COM+ON"))
    {
      communicationEnabled = true;
      Serial.println("Communication enabled.");
    }
    else if (HC12Zprava.startsWith("COM+OFF"))
    {
      communicationEnabled = false;
      Serial.println("Communication disabled.");
    }
    else if (HC12Zprava.startsWith("AT")) 
     {
      // nastavení konfiguračního módu s pauzou pro zpracování
      digitalWrite(pinSet, LOW);
      delay(100);
      // vytištění konfigurační zprávy po sériové lince pro kontrolu
      Serial.print(serialZprava);
      // nastavení konfigurace pro lokálně připojený modul s pauzou pro zpracování
      HC12.print(HC12Zprava);
      delay(500);
      digitalWrite(pinSet, HIGH);
      // přechod zpět do transparentního módu s pauzou na zpracování
      delay(100);
      // odeslání informace do druhého modulu o úspěšném novém nastavení
      HC12.println("Vzdalena konfigurace probehla v poradku!");
    }
    else
    {
      Serial.print(HC12Zprava);
    }

    HC12Zprava = "";
    HC12KonecZpravy = false;
  }

  
  if (communicationEnabled && currentTime - lastTransmissionTime >= 100)
    {
      if (ss.available() > 0)
      {
        if (gps.encode(ss.read()))
        {
          if (gps.location.isValid())
          {
            // Transmit data via HC12
            transmitDataHC12();

            // Write data to SD card
            if (sdEnabled) {
              writeDataToFile();
            }
            // Print data to Serial
            printDataToSerial();

            lastTransmissionTime = currentTime;
          }
          else
          {
            Serial.println(F("INVALID"));
          }
          
        }
      }
    }
}

void transmitDataHC12() {
  // Code to transmit data via HC12
      HC12.print(bme.readTemperature());
      HC12.print(bme.readHumidity());
      HC12.print(";");
      HC12.print(";");
      HC12.print(bme.readPressure() / 100.0F);
      HC12.print(";");
      HC12.print(gps.location.lat(), 6);
      HC12.print(F(";"));
      HC12.print(gps.location.lng(), 6);
      HC12.print(F(";"));
      HC12.print(gps.time.hour());
      HC12.print(F(":"));
      HC12.print(gps.time.minute());
      HC12.print(F(":"));
      HC12.print(gps.time.second());
      HC12.print(F("."));
      HC12.print(gps.time.centisecond());
      HC12.print(";");
      HC12.print(gps.speed.kmph());
      HC12.print(";");
      HC12.print(gps.altitude.meters());
      HC12.println();
}

void writeDataToFile() {
  // Write data to the file
  dataFile = SD.open("/data.csv", FILE_APPEND);
  if (dataFile) {
    dataFile.print(bme.readTemperature());
    dataFile.print(";");
    dataFile.print(bme.readHumidity());
    dataFile.print(";");
    dataFile.print(bme.readPressure() / 100.0F);
    dataFile.print(";");
    dataFile.print(gps.location.lat(), 6);
    dataFile.print(F(";"));
    dataFile.print(gps.location.lng(), 6);
    dataFile.print(F(";"));
    dataFile.print(gps.time.hour());
    dataFile.print(F(":"));
    dataFile.print(gps.time.minute());
    dataFile.print(F(":"));
    dataFile.print(gps.time.second());
    dataFile.print(F("."));
    dataFile.print(gps.time.centisecond());
    dataFile.print(";");
    dataFile.print(gps.speed.kmph());
    dataFile.print(";");
    dataFile.print(gps.altitude.meters());
    dataFile.println();
    dataFile.close();
  }
  else {
    dataFile.close();
  }
}

void printDataToSerial() {
  // Print data to Serial
  Serial.print(bme.readTemperature());
  Serial.print(";");
  Serial.print(bme.readHumidity());
  Serial.print(";");
  Serial.print(bme.readPressure() / 100.0F);
  Serial.print(";");
  Serial.print(gps.location.lat(), 6);
  Serial.print(F(";"));
  Serial.print(gps.location.lng(), 6);
  Serial.print(F(";"));
  Serial.print(gps.time.hour());
  Serial.print(F(":"));
  Serial.print(gps.time.minute());
  Serial.print(F(":"));
  Serial.print(gps.time.second());
  Serial.print(F("."));
  Serial.print(gps.time.centisecond());
  Serial.print(";");
  Serial.print(gps.speed.kmph());
  Serial.print(";");
  Serial.print(gps.altitude.meters());
  Serial.println();
}

And here is the cide for the receiver.

//rx
#define RXD2 16 //(RX2)
#define TXD2 17 //(TX2)
#define pinSet 4 //set
#define HC12 Serial2 //Hardware serial 2 on the ESP32
char serialZnak;
char HC12Znak;
String serialZprava = "";
String HC12Zprava = ""; //to co mi vyplivne HC-12
boolean serialKonecZpravy = false;
boolean HC12KonecZpravy = false;

void setup()
{
  // nastavení pinu Set jako výstupního
  pinMode(pinSet, OUTPUT);
  // nastavení transparentního módu pro komunikaci
  digitalWrite(pinSet, HIGH);
  // pauza pro spolehlivé nastavení módu
  delay(80);
  // zahájení komunikace po sériové lince
  Serial.begin(9600);
  // zahájení komunikace s modulem HC-12
  HC12.begin(9600, SERIAL_8N1, RXD2, TXD2); // Serial port to HC12
}

void loop()
{
  while (HC12.available())
  {
    HC12Znak = HC12.read();
    HC12Zprava += char(HC12Znak);
    if (HC12Znak == '\n')
    {
      HC12KonecZpravy = true;
    }
  }

  while (Serial.available())
  {
    serialZnak = Serial.read();
    serialZprava += char(serialZnak);
    if (serialZnak == '\n')
    {
      serialKonecZpravy = true;
    }
  }

  if (serialKonecZpravy)
  {
    if (serialZprava.startsWith("COM+ON"))
    {
      Serial.println("Communication enabled.");
      HC12.println("COM+ON");
    }
    else if (serialZprava.startsWith("COM+OFF"))
    {
      Serial.println("Communication disabled.");
      HC12.println("COM+OFF");
    }
    else if (serialZprava.startsWith("AT")) {
      HC12.print(serialZprava);
      delay(100);
      digitalWrite(pinSet, LOW);
      delay(100);
      Serial.print(serialZprava);
      HC12.print(serialZprava);
      delay(500);
      digitalWrite(pinSet, HIGH);
      delay(100);
    }
    else
    {
      HC12.print(serialZprava);
    }

    serialZprava = "";
    serialKonecZpravy = false;
  }

  if (HC12KonecZpravy)
  {
    if (HC12Zprava.startsWith("AT")) {
      digitalWrite(pinSet, LOW);
      delay(100);
      Serial.print(serialZprava);
      HC12.print(HC12Zprava);
      delay(500);
      digitalWrite(pinSet, HIGH);
      delay(100);
      HC12.println("Vzdalena konfigurace probehla v poradku!");
    }
    else
    {
      Serial.print(HC12Zprava);
    }
    HC12Zprava = "";
    HC12KonecZpravy = false;
  }
}
2

Is this should be

      HC12.print(bme.readTemperature());
      HC12.print(";");
      HC12.print(bme.readHumidity());
      HC12.print(";");
4

Yeah, thanks but I already found this mistake and it didn't resolve my problems. I'm still grateful for your help

5

It is not a good idea to change any wiring, or change system status, for example by removing an SD card, while the MCU is running.

The code libraries are primitive and are not designed to handle situations like this, unless used VERY wisely.

You have lots of useless delay statements in the code. The delay() function should be used only when necessary.

6

Thanks! Should I just delete all the delay() functions then?

7

You can keep the necessary delays(), but they should be no longer than required.

8

Okay, I tried that but the delay with GPS doesn't work. I want it to send data twice a second but when I set the delay to 500ms it sends every kinda randomly. For example the time in the one line is 2 seconds behind the next line but sometimes even 3 or 4 second and sometimes it's only 1 second behind.

9

Delays should never be needed or used with TinyGPS running. Use millis() to time events instead.

10

Can you show how to do that? Some easy example will be enough.

11