HM-10 BLE module not responding to AT command – tried everything (UNO + SoftwareSerial)

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1

Hi! I recently got an HM-10 BLE module to use in a project with an Arduino UNO board (I mainly need to find a signal, record and display the RSSI).
Since I'm not good at coding this stuff I looked at some tutorials online and also asked ChatGPT and Gemini to write some basic sketches to test the module.

All the sources I found use the SoftwareSerial library for the communication between the board and the module.

After wiring everything correctly (I double-checked many times, also using the official documentation for the HM-10), I tried to test the module by sending the AT command. Unfortunately, I never get the expected OK response.

The BLE module seems to work just fine — I can see it from my phone with Bluetooth scanning apps — but the problem is serial communication.

To isolate the problem, I:

  • tried loopback tests between TX and RX pins using SoftwareSerial
  • tried different pin pairs (2↔3, 10↔11, etc.)
  • tried with two different UNO boards (original and Elegoo)
  • tried on two different PCs (Windows)
  • used two separate USB cables
  • tried both Arduino IDE 1.8 and 2.x
  • rebooted the system and made sure no other program was interfering with the COM port

In all tests, whenever I send something through the Serial Monitor, the RX LED blinks, but I never receive any data back on the Serial Monitor.

I'm attaching two minimal test sketches that I used:

Sketch 1: Test communication with HM-10 using SoftwareSerial:

#include <SoftwareSerial.h>

// HM-10: TX -> pin 10 | RX <- pin 11 (use a voltage divider on HM-10 RX)
SoftwareSerial BTSerial(10, 11); // RX, TX

void setup() {
  Serial.begin(9600);
  BTSerial.begin(9600);
  Serial.println("Sending AT command to HM-10...");
  delay(1000);
  BTSerial.println("AT"); // Send AT command
}

void loop() {
  // Forward HM-10 response to Serial Monitor
  if (BTSerial.available()) {
    char c = BTSerial.read();
    Serial.print(c);
  }
}

Wiring details:

  • HM-10 VCC → 5V (datasheet says it supports 3.3–6V input)
  • HM-10 GND → GND
  • HM-10 TX → Arduino RX pin (e.g., pin 10)
  • HM-10 RX ← Arduino TX pin (e.g., pin 11) — using voltage divider (1kΩ + 2kΩ)
  • USB connected to PC for Serial Monitor

Sketch 2: SoftwareSerial loopback test:
I connected pin 2 to pin 3 directly (used a jumper wire)

#include <SoftwareSerial.h>

SoftwareSerial testSerial(2, 3); // RX, TX

void setup() {
  Serial.begin(9600);
  testSerial.begin(9600);
  Serial.println("Sending message via SoftwareSerial loopback...");
  testSerial.println("Loopback test message");
}

void loop() {
  if (testSerial.available()) {
    char c = testSerial.read();
    Serial.print("Received: ");
    Serial.println(c);
  }
}

I’m running out of ideas here :sweat_smile:.
Any help or suggestions would be greatly appreciated ! Thank you :folded_hands:

2

Please post schematics. Words are not good enough.

3

Hello,

What baudrate did you try? Only 9600bps? You could try with pretty much every option you have

Else, you could take a look at this. This is in French but maybe you can understand, or ask someone (chatGPT lol) to translate it for you

4

Seems is the word. All you really know is that the power is on.

1 make sure the divider is the right way round - 2k between Rx and Gnd.

2 be sure you have a BLE terminal on the phone. That by Morisch is the favourite of the moment. It needs to be set correctly.

3 You haven't said if the module works OK in communications mode?

4 9600 is the ONLY baud rate for AT configuration

5

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