Hello everyone,
I am trying to interface an ESP32 with a SIMCOM A7670C GSM/4G module, but I am not receiving proper responses to AT commands. Sometimes I only see ATREADY: 1, but after that no reply comes. In Some time It's Showing Continuously ATREADY: 1 Response.
Here are my details:
Hardware Setup: -
- GSM Module: SIMCOM A7670C (LTE module, version E)
- MCU: ESP32 Devkit
- Power Supply:
- DC-DC Buck Converter set to 4.0V output
- Multimeter readings: 1.6A current consumption when module is ON
- Voltage remains stable at ~4.0V during operation
- Connections:
- VCC → 4.0V from buck converter
- GND → Common ground with ESP32
- TX (A7670) → RX (GPIO16 of ESP32)
- RX (A7670) → TX (GPIO17 of ESP32)
- PEN → 3.3V
- NETLIGHT → LED (blinks continuously)
- PWRKEY → GPIO4 of ESP32 (pulled LOW to turn ON)
Software Setup: -
Arduino IDE, Code 1 Serial configured at 115200 baud:
#include <SoftwareSerial.h>
SoftwareSerial sim(21,22);
void setup() {
Serial.begin(115200); // USB Serial Monitor
Serial.println("=== GSM AT Command Test Start ===");
delay(2000);
sim.println("AT"); // Basic Test
delay(1000);
sim.println("ATI"); // Module Info
delay(1000);
sim.println("AT+CPIN?"); // SIM Status
delay(1000);
sim.println("AT+CREG?"); // Network Status
}
void loop() {
if (sim.available()) {
Serial.write(sim.read());
}
if (Serial.available()) {
sim.write(Serial.read());
}
}
Arduino IDE, Code 2 Serial configured at 115200 baud:
#include <HardwareSerial.h>
HardwareSerial modem(1);
#define PWRKEY 4
void setup() {
// put your setup code here, to run once:
pinMode(PWRKEY, OUTPUT);
digitalWrite(PWRKEY, HIGH);
delay(100);
digitalWrite(PWRKEY, LOW);
delay(1500);
digitalWrite(PWRKEY, HIGH);
Serial.begin(115200);
modem.begin(115200, SERIAL_8N1, 21,22);
Serial.print("Sending AT... ");
delay(3000);
modem.println("AT");
}
void loop() {
// put your main code here, to run repeatedly:
if(modem.available()){
Serial.write(modem.read());
}
if(Serial.available()){
modem.write(Serial.read());
}
}
Arduino IDE, Code 3 Manual AT Command Sending From Serial Monitor Serial configured at 115200 baud:
#include <HardwareSerial.h>
HardwareSerial testSerial(1);
void setup() {
Serial.begin(115200);
testSerial.begin(115200, SERIAL_8N1, 21,22); // RX=16, TX=17
Serial.println("Type something below:");
}
void loop() {
while (Serial.available()) {
char c = Serial.read();
testSerial.write(c); // USB → TX
}
while (testSerial.available()) {
char c = testSerial.read();
Serial.write(c); // RX → USB
}
}
I am Trying These 3 Code One By One To Check Module is Working or not
Problem Observed
- When powered, the NETLIGHT LED keeps blinking continuously (does not stabilize).
- Sometimes I see
ATREADY: 1message, but when I sendAT, no OK response comes. - Without breadboard, the module powers ON once, then LED stops blinking and never comes back ON.
- With breadboard + buck converter, LED blinks continuously but still no AT responses.
- Power seems enough (4.0V, 1.6A measured).
My Questions
- Any Power Supply Issue the Module Is Continue Reset or not Connecting to Network.
- Is my wiring correct (specially PWRKEY and PEN pins)?
- Do I need a different sequence to power ON A7670?
- Why is the module only sending
ATREADY: 1but not responding toATcommands? - Is my buck converter sufficient, or should I use a Li-Ion battery for better current stability?
Any help, guidance, or working example code for ESP32 + A7670 would be greatly appreciated 
Thanks in advance!
