ESP32 Forum

Posted: **Thu Oct 09, 2025 3:59 pm**

Problem Description:
I'm trying to establish communication between an ESP32-C6 and a SIMCOM A7670C module, but I’m not getting any response to AT commands.
The module appears to be powered on (LED is blinking), but it doesn’t respond to any AT commands sent from the ESP32-C6.

Hardware Setup:
MCU: ESP32-C6
Cellular Module: SIMCOM A7670C
Development Environment: Arduino IDE 2.3.6

Wiring:
SIM TX → GPIO4 (ESP RX)
SIM RX → GPIO5 (ESP TX)
GND → GND
VCC → 5V (also tried 3.3V)

Code I've Tried:

#define SIM_TX_PIN 4
#define SIM_RX_PIN 5
HardwareSerial simSerial(1);
void setup() {
Serial.begin(115200);
simSerial.begin(115200, SERIAL_8N1, SIM_RX_PIN, SIM_TX_PIN);
}
void loop() {
// Send data from Serial Monitor to SIM module
if (Serial.available()) {
String command = Serial.readStringUntil('\n');
simSerial.println(command);
Serial.print("Sent: ");
Serial.println(command);
}
// Read data from SIM module and print to Serial Monitor
if (simSerial.available()) {
String response = simSerial.readString();
Serial.print("Received: ");
Serial.println(response);
}
}

Issue:
Even though the wiring and code seem correct, I’m not receiving any response from the SIMCOM module.
The same module works fine when connected to a DOIT ESP32 DevKitV1 (classic) using the same code and Arduino IDE setup.

Could anyone please suggest what might be causing this issue or if there’s any difference in UART handling on the ESP32-C6.
We would truly appreciate your help and guidance.

Posted: **Fri Oct 10, 2025 4:10 pm**

If you have USB connected, and set the IDE to use HWCDC, them Serial will get attached to that. Try using Serial1 instead of Serial (aka Serial0)

Posted: **Sat Oct 11, 2025 5:11 am**

try this code

Code: Select all

// ESP32-C6_Dev_Board SIM_A7670E Serial1 test - for loopback test connect pins RX and TX
// https://learn.adafruit.com/adafruit-esp32-c6-feather/pinouts

// NOTE: enable "USB CDC on Boot"
// NOTE: SIM_A7670E requires 5V power

#define RXD1 4    // RX
#define TXD1 5    // TX

// for RS232 shield connect
// ESP32 RXD1 to TTL/RS232 Rx
// ESP32 TXD1 to TTL/RS232 Tx
// connect GND pins together and VCC to 3.3V on ESP32 5V on UNO ect
// for loopback test connect 9-pin D_type connector pins 2 Tx to 3 Rx (pin 5 is GND)

void setup() {
  // initialize both serial ports:
  Serial.begin(115200);
  delay(1000);
  Serial1.begin(115200, SERIAL_8N1, RXD1, TXD1);
  Serial.printf("\n\nESP32-C6 serial1  test RXD1 pin %d TXD1 pin %d\n", RXD1, TXD1);
  Serial.printf(" loopback test connect pin %d to pin %d\n", RXD1, TXD1);
  Serial.printf("RS232: ESP32 pin %d RXD1 to TTL/RS232 Rx and pin %d TXD1 to TTL/RS232 Tx\n", RXD1, TXD1);
  Serial.printf("RS232 - loopback connect 9-pin D-type pin 2 Tx to pin 3 Rx\n");
}

void loop() {
  // read from Serial1, send to Serial
  if (Serial1.available()) {
    int inByte = Serial1.read();
    Serial.write(inByte);
  }
  // read from Serial, send to Serial1
  if (Serial.available()) {
    int inByte = Serial.read();
    //Serial.write(inByte);     // local echo if required
    Serial1.write(inByte);
  }
}

typing AT commands gives

Code: Select all

*ATREADY: 1

+CPIN: SIM REMOVED
AT
OK
AT+CGMI
SIMCOM INCORPORATED
OK
AT+CGMR
+CGMR: A131B03A7670M6C
OK
AT+CGMM
A7670E-LASA
OK
AT+CSQ
+CSQ: 16,99
OK

Posted: **Mon Oct 13, 2025 10:59 am**

Hi,

Thanks for your quick reply earlier. I tried running the code you provided, but I’m not getting the expected result.
When I send the “AT” command, I do not receive the “OK” response from the SIMCOM A7670C module.

Here are my setup details:
ESP Board: ESP32-C6-DevKitM-1 V1.0 (www.espressif.com)
SIM Module: SIMCOM_A7670C
Connections: Same as previously shared (SIM TX → GPIO4, SIM RX → GPIO5, GND → GND, VCC → 5V)
Programming Method: Using USB Type-C cable directly to the ESP32-C6 board

You mentioned in your note:
// NOTE: enable "USB CDC on Boot"
// NOTE: SIM_A7670E requires 5V power

Could you please guide me where I can find or enable the “USB CDC on Boot” option before flashing the code?
Are there any other settings or configurations that need to be enabled in Arduino IDE or ESP-IDF before uploading the sketch. Please also confirm which ide you are using Arduino IDE or ESP-IDF?

Thank you for your help and guidance.

ESP32 Forum

No Response from SIMCOM A7670C When Connected to ESP32-C6 via UART (Arduino IDE)

No Response from SIMCOM A7670C When Connected to ESP32-C6 via UART (Arduino IDE)

Re: No Response from SIMCOM A7670C When Connected to ESP32-C6 via UART (Arduino IDE)

Re: No Response from SIMCOM A7670C When Connected to ESP32-C6 via UART (Arduino IDE)

Re: No Response from SIMCOM A7670C When Connected to ESP32-C6 via UART (Arduino IDE)