[solved with workaround] HC-05 connected in data mode but cannot read or write data

Projects Networking, Protocols, and Devices
1

I am able to set everything in the AT mode, and I am able to get it connected to my MacBook (state pin returns HIGH), HC05 blinks like 1 0 1 0 0 with one second interval. The connections are:
Arduino RX - HC05 TX
Arduino TX - HC05 RX
5v - HC05 VCC
I don't use a voltage divider, just keep it simple.

I removed everything else and have the simplest code to demo here:

#include <SoftwareSerial.h>

SoftwareSerial HC05(5, 6);
 
void setup() 
{  
  Serial.begin(9600);
  HC05.begin(38400);
  Serial.println("ready");  
} 

void loop() 
{ 
  HC05.write('=');
  Serial.write('.');
  delay(1000);
}

I can connect to the device with /dev/tty.HC-05 with screen or coolTerm, but I cannot see any data coming from the Bluetooth module. What to look at now?

2

When in AT mode, you set the communication baud rate to 38400? The usual default communication baud rate is 9600.

3

I tried 38400, 9600 with 8 bits, no parity, 1 bit stop.
I found something wrong with my existing projects, so I just picked up this module and inspect it again recently, it was working two years ago. I tried another HC05 module, same problem.

4

What Arduino are you using? The pins available for software serial can vary?

Arduino RX - HC05 TX
Arduino TX - HC05 RX
#include <SoftwareSerial.h>
SoftwareSerial HC05(5, 6);

The Software Serial constructor is from the point of view of the Arduino. Can you provide a simple sketch of how you have connected things?

SoftwareSerial(rxPin, txPin, inverse_logic)
5

i am pretty sure wiring is correct，have been using hc05 for a while, It just stops working with my Monterey upgrade. I used a logic analyzer to analyze the pins, I can see a character '=' is sent to the TX pin to the HC05 module every second.

Screen Shot 2022-09-27 at 21.33.47
Screen Shot 2022-09-27 at 21.33.471886×318 32.3 KB

0x3d is actually the ASCII code of '=' in my test program.

Screen Shot 2022-09-27 at 21.33.56
Screen Shot 2022-09-27 at 21.33.56748×846 74.9 KB

Nothing is wrong at the HC05 or arduino side. Why I cannot see it from my MacBook terminal?

Update: somebody found the same problem:

I think it's some kind of bug in Monterey. It's annoying but now it works.

6

This topic was automatically closed 180 days after the last reply. New replies are no longer allowed.