Two HC-05 modules won't stay paired

Projects Networking, Protocols, and Devices
14

Back from a short fishing trip. The problem of never completing uploading was solved by simply removing the wires from the RX and TX (pins 0 and 1) when uploading.

I think the UNO, with only one hardware serial port, is not the best for what I'm trying to do because the port is shared by the USB connection (if I understand this correctly). So I decided to try using SoftwareSerial for my connection to the HC-05. I have the TX and RX pins on the HC05 connected to UNO pins 2 and 3, respectively.

Pushing the button changes the buttonState variable successfully. However, mySerial.available and mySerial.availableForWrite return a zero, and prevState never changes. (The LED on the master doesn't change either).

What value should I get from mySerial.available and mySerial.availableForWrite? What am I doing wrong?

PXL_20250512_140731453
PXL_20250512_1407314531920×2560 111 KB

#include <SoftwareSerial.h>
SoftwareSerial mySerial(2, 3); // RX, TX
const int button = 8;
int buttonState = 0;
int prevState = 0;

void setup() 
{
  pinMode(button, INPUT_PULLUP);
  
  // Set data rate for the serial monitor:
  Serial.begin(9600); 
  delay(5);
  // set the data rate for the SoftwareSerial port to match the UART baud on HC05
  mySerial.begin(38400);
  delay(5);
}
void loop() 
{
    // Reading the button
    buttonState = digitalRead(button);
    Serial.print("buttonState = ");
    Serial.println(buttonState);
    Serial.print("prevState = ");
    Serial.println(prevState);
    Serial.print("mySerial.availableForWrite = ");
    Serial.println(mySerial.availableForWrite());
    delay(1000);
    if (buttonState != prevState) // if button has been pushed or released
    {
        if (buttonState == LOW && (mySerial.availableForWrite()>0)) // becomes LOW when button is pushed
        {
            mySerial.write('1'); // Sends '1' to the master to turn on LED
            prevState = LOW;
            delay(5); 
        }
        else if (buttonState == HIGH && (mySerial.availableForWrite()>0))
        { 
            mySerial.write('0');
            prevState = HIGH;
            delay(5);
        } 
    }
      
}