ESP32-S3 as USB Host for Quectel EG800Q Modem – Communication Issue

[Noval-Boby]

I’m trying to use an ESP32-S3 as a USB Host to communicate with a Quectel EG800Q 4G modem via its USB interface.

I’ve already tested several available USB Host libraries for the ESP32-S3 (including USBHost, USBH_CDC, and others), but:

Some of them fail to compile in Arduino IDE, and

Others compile but don’t receive any response from the modem after initialization.

I also tried using the example USB CDC Host sketches, but the modem doesn’t seem to respond to AT commands.

My questions:

Is there a working method or example to communicate with a USB modem (like EG800Q) using the ESP32-S3’s native USB Host interface in Arduino or ESP-IDF?

If not directly supported, is there an alternative approach to send and receive AT commands over USB .

[bertmelis]

This library is specific for CDC devices or the 3 mentioned VCP drivers. What happens if you use this library and connect your modem?

Would you be able to get more device info from the modem? There is no driver available for ESP-IDF and if you want to communicate over UART/USB you need the baudrate and all.

[Noval-Boby]

#include <Arduino.h>
#define GSM_PWR_CTRL 48 // Power control pin
#define GSM_PWRKEY 47 // PWRKEY pin
#include <USBHostSerial.h>
#define USBHOSTSERIAL_BUFFERSIZE 1024
USBHostSerial usbSerial;

void setup() {
Serial0.begin(115200);
delay(2000);
Serial0.println(" Modem pulse starting ");

// Modem power sequence
pinMode(GSM_PWR_CTRL, OUTPUT);
pinMode(GSM_PWRKEY, OUTPUT);

digitalWrite(GSM_PWR_CTRL, HIGH);
digitalWrite(GSM_PWRKEY, HIGH);
delay(100);
Serial0.println("Power pin of modem set as HIGH");
digitalWrite(GSM_PWRKEY, LOW);
delay(100);

Serial0.println("Powering modem ON...");
digitalWrite(GSM_PWRKEY, HIGH);
digitalWrite(GSM_PWR_CTRL, LOW);
delay(700);
digitalWrite(GSM_PWRKEY, LOW);
Serial0.println("Power pulse completed");

Serial0.println("Waiting for modem to boot (15 seconds)...");
delay(15000);
/*
baudrate
stopbits: 0: 1 stopbit, 1: 1.5 stopbits, 2: 2 stopbits
parity: 0: None, 1: Odd, 2: Even, 3: Mark, 4: Space
databits: 8
*/
usbSerial.begin(115200, 0, 0, 8);

delay(2000);
}

void loop() {
// send message every 10s
static uint32_t lastMessage = 0;
if (millis() - lastMessage > 10000) {
lastMessage = millis();
const char message[] = "AT\r\n";
usbSerial.write((uint8_t*)message, 4);
}

if (usbSerial.available()) {
uint8_t buff[256];
std::size_t len = 0;
while (usbSerial.available() && len > 0) {
len += usbSerial.read(&buff[len], 256 - len);
}
for (size_t i = 0; i < len; i++) {
Serial0.write(buff[i]); // sends byte to PC over UART0
}
}
}
when i use this , i get no return for my AT command

Quectel_EG800Q_Series_Hardware_Design_V1.2.pdf

i attached the modem datasheet, i think most modem support CDC modem

[bertmelis]

1. Use the develop version if this lib
2. Define USBHOSTSERIAL_CDC_MODE to 1 (in your build chain or change the header file)
3. Add some logging to the USB library: https://github.com/bertmelis/USBHostSerial/blob/develop/examples/logging/logging.ino

Report back: the library might just not recognize the modem. We don't know now.

[Noval-Boby]

USB setup done
i got this message from some where , but got no replay to my AT commands

also got this
16:04:15.962 -> USB setup done
16:04:16.348 -> E (18932) ENUM: Configuration descriptor larger than control transfer max length
16:04:16.348 -> E (18933) ENUM: [0:0] CHECK_SHORT_CONFIG_DESC FAILED

[bertmelis]

See here: espressif/esp-idf#9868

idf.py menuconfig Component config -> USB-OTG -> Largest size (in bytes) of transfers to/from default endpoints

Set the value you need