I have recently started working with the Arduino Pro Mini 5v/16Mhz and an AT 09 BLE module for an IoT project. I am controlling the BLE module using Software Serial and am leaving the hardware serial for for my laptop. I am using an app called "Serial Bluetooth Terminal" on Android to send/receive messages. The BLE module is able to receive messages and the "AT" command is also working. But when I try to get the BLE module to send a message, I get no response in the app. Any idea why this is happening and how can I resolve it?

My connections are:

Laptop -> Arduino UNO, MB-102(USB to breadboard power adapter)
Arduino UNO(without IC) Rx -> Pro mini Tx0
Arduino UNO(without IC) Tx -> Pro mini Rx1
Arduino UNO(without IC) RESET -> Pro mini Rst
MB-102 5V -> Pro Mini Pin RAW
MB-102 GND -> Pro Mini Pin GND
Pro Mini Pin 2 -> AT 09 TXD
Pro Mini Pin 3 -> AT 09 RXD
Pro Mini Pin VCC -> AT 09 VCC
Pro Mini Pin GND -> AT 09 GND

This is my code:


SoftwareSerial ble(2, 3);

int statePin = 4;
char c;
void setup() 

void loop() 
  while(ble.available() > 0)
    c = char(ble.read());

This is the first time I am posting here so please tell me if I missed out on any information.

  • You have not connected the STATE signal?
    – timemage
    Commented May 17, 2021 at 10:44
  • 1
    Yes. That is correct. Was I supposed to? Edit: The state pin does not seem to be doing anything. It seems to be grounded irrespective of connection status. Verified with a multimeter.
    – Flight64
    Commented May 17, 2021 at 12:42

1 Answer 1


So my AT 09 module is most likely faulty. I got a new HM 10 and connected it without changing any connections or code and it worked like a charm. I do not know the exact nature of the defect but since the chip was responding to commands, I think the PCB might have been damaged.

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