Interfacing Raspberry Pi 5G HAT with other controller

Hi Meera,

I've not used that particular Pi HAT, but I have used another WaveShare Pi HAT (for 4G/LTE), and the easiest way to interface was to use the on-board USB-UART. I too didn't use Pi. I see your board also has a USB connector, although it's weird that it is a USB Type-A connector. Mine had a micro USB connector.

Waveshare has put the USB connector specifically for testing out using the UART, so if that doesn't work, then that needs to be resolved first. 

For the HAT board I used, I could see in Windows a "SimTech" device appear under Other Devices, and I could connect to it from a serial terminal (PuTTY etc). Then you can use the command manual to see what AT commands are available.

Thanks for the info shabaz . To use the on-board USB-UART, i can connect the USB UART to the microcontroller, right? Is there a specific model of USB-UART. For now i am using this model

https://my.cytron.io/p-uc00a-ftdi-usb-to-uart-converter?gad_source=1&gclid=CjwKCAjwx-CyBhAqEiwAeOcTdRxSOY-CX4LD6aRlMMRgviPsTpmzslS7RD6DMOrFXi9oXp66woBFOBoC4xAQAvD_BwE

And i am using the code below for the handshake

// Need this for the lower level access to set them up.
#include <HardwareSerial.h>

//Define two Serial devices mapped to the two internal UARTs
HardwareSerial MySerial0(0);

void setup()
{
    // For the USB, just use Serial as normal:
    Serial.begin(115200);

    // Configure MySerial0 on pins TX=D6 and RX=D7 (-1, -1 means use the default)
    MySerial0.begin(115200, SERIAL_8N1, -1, -1);
   // MySerial0.print("MySerial0");
//while(!Serial);
    Serial.println("Initializing 5G module...");
     Serial.println("Sending AT command...");
    MySerial0.write("AT\r");  
// Send AT command to check communication
    delay(1000);

     // Check response from 5G module
    while (MySerial0.available()) {
        char c = MySerial0.read();
        Serial.print(c);


}

But somehow i am not getting any response from the 5G module. Below is the current setup.

The XIAO USB is connected to the PC. The RX and TX pin of the XIAO is connected to USB to UART converter. And the USB port on the UART is connected to the 5G module.

Hi,

I was thinking initially test the AT commands from a Windows machine, and then once that works, you could skip the USB connection, and use the normal UART interface directly from a microcontroller.

You could use Windows in two ways;(1) use a USB connector on the Pi HAT, but it's weird to me that it is Type A. or (2) using the USB-UART module in your photo, connected to the UART pins on the HAT on the 40-way connector. 

If you're using your code above with your microcontroller, then you need to connect the microcontroller directly to the UART pins on the 40-way connector on the HAT, no need for any USB.

However, looking at the code, are you sure the baud rate is 115200? I've not looked at the documentation for the 5G board, but the 4G/LTE board defaulted to 9600 baud. Also, I needed terminator \r\n whereas your code is slowing just \r. My 4G board also used a (different) SimCom module, so perhaps the terminator is similar.

Thanks for the suggestion shabaz . Now i am connecting my controller directly to the 5G module through the 40-way pin( RX and TX pin).

I have also updated the code as below

// Need this for the lower level access to set them up.
#include <HardwareSerial.h>

//Define two Serial devices mapped to the two internal UARTs
HardwareSerial MySerial0(0);

void setup()
{
    // For the USB, just use Serial as normal:
    Serial.begin(9600);

    // Configure MySerial0 on pins TX=D6 and RX=D7 (-1, -1 means use the default)
    MySerial0.begin(9600, SERIAL_8N1, -1, -1);
   // MySerial0.print("MySerial0");
//while(!Serial);
    Serial.println("Initializing 5G module...");
     Serial.println("Sending AT command...");
    MySerial0.write("AT\r\n");  
// Send AT command to check communication
    delay(1000);

     // Check response from 5G module
    while (MySerial0.available()) {
        char c = MySerial0.read();
        Serial.print(c);  


}
}
void loop()
{

}

But i am getting this response

Not sure if the DIP switch may need adjustment. Also, I could not see if D5 needs to be driven high or low. But worth investigating that, if there's any info or schematic.

I will check on that pins and update you back if there is any progress. Thanks againshabaz . Really appreciate your help.

shabaz , just want to know if i were to use the UART to USB module instead of connecting directly to the UART pin on 40-way connecter, what changes do i need to make in the software or the hardware?

Thank you in advance for the help.

I believe I've the same LTE board Shabaz has mentioned. USB port in that board can be used to create multiple virtual ports including AT command port, diagnostic port, audio channel and GPS. If you have any microcontroller that has support USB for communication, you can enumerate the port, select the AT command port and exchange data over it. ESP32C3 doesn't support USB communication as far as I know, ESP32S3 does. The board I've has a dedicated USB to TTL section uses a CP2102 USB to TTL converter, so I assume if you use the same converter, it might work.

You'd need to have USB host capability on the microcontroller, which is less usual, and is another thing to troubleshoot, so it's not usually worth doing, especially since the microcontroller will already have a normal UART peripheral, so it's best to stick with that. 

However, if you meant for testing on Windows, then personally I would not try to reuse that code, because you can test on Windows using a serial console (like PuTTY), or, automate with Python, because that will be far quicker to try out things, than using C. 

For instance, you could write a Python function to open the serial port, and another Python function to write a string, and another to read from the serial port, and then you can on-the-fly issue the functions from the Python command line. Usually that's my preferred method of testing such types of things, using Python either from Windows, or from MicroPython (using a Pi Pico). 

Can you please try the following snippet for sending AT command over the UART connection you've made here?

char *at_check = "AT\r\n";

MySerial0.printf("%s", at_check);

//delay(1000); don't use delay here.

while(MySerial0.available())

{

String at_response = MySerial0.readString();

Serial.println(at_response);

}