SIM7600 A-H not responding directly when connected through pins

Question

I am working on a project which utilizes three components:

1. Arudino Pro Mini(5v)
2. Breakout SIM7600 A-H from AND technologies
3. 9V Battery (connected to RAW and GND on the Arduino board)

I am trying to communicate through the device using the pins provided on the SIM board, which unfortunately is not successful.

I am able to connect to the board directly using an usb-c cable. After installing the right drivers, I am able to communicate with the board using AT commands from my Windows PC.

However, I want to be able to send AT commands through the arduino. The set up looks like this: I connect the following pins of arduino mini and SIM 7600A-H.

• SIM 7600 TXD --> Arduino Pin 2
• SIM 7600 RXD --> Arduino Pin 3
• SIM 7600 Supply --> 5V
• SIM 7600 GND --> GND

The code that I am using, I tried it with every possible baud rate:

#include <SoftwareSerial.h>
SoftwareSerial mySerial(2, 3); // RX, TX
void setup() {
 // Open serial communications and wait for port to open:
 Serial.begin(115200);
 while (!Serial) {
 ; // wait for serial port to connect. Needed for native USB port only
 }
 Serial.println("Goodnight moon!");
 // set the data rate for the SoftwareSerial port
 mySerial.begin(115200);
}
void loop() { // run over and over
 if (mySerial.available()) {
 Serial.write(mySerial.read());
 }
 if (Serial.available()) {
 mySerial.write(Serial.read());
 }
}

After sending an AT command, there is no response, the module has both LED's on, indicating that it is up and running.

• jsotola: please describe the 9 V battery
• Peter Paul Kiefer: First a warning: Have you read the datasheet from the link above. The TX and RX pins of the SIM 7600 are 3.3V and your mini is a 5V one. The worst case scenario is that the mini killed the RX pin hardware. The best case failure scenario is that the SIM TX Pin has not enough volts to safely signal a HIGH Level to the mini RX pin.
• Peter Paul Kiefer: If you powered the SIM over the VCC of the mini then you have only 150mA current available (for the mini and the SIM module). That would be a problem. The SIM module needs a peak current of about 2A (I got the value from other forums, I found no reliable specification). That is not drawn for a long time only for sending. But I fear the 150 mA would also not suffice for the standby mode.
• Peter Paul Kiefer: If you could connect over USB you know the Baud rate to the SIM module. The Baud rate of the mini's connection to the PC must be set to the rate that you selected in the Arduino IDE or the Serial Terminal you use. There is no need to try out others.
• Peter Paul Kiefer: About your code: I personally would move the mySerial.begin(115200); right below the Serial.begin(115200);. Just to keep and see them together. The while (!Serial) { statement could be a problem. As written in the comment beneath the statement, it is only necessary for native USB connection but on a pro mini you have a 328P MCU that is connected to a USB to Serial converter and not to a native USB. Perhaps it blocks and your code is not executed.

Answer 1

Is your issue resolved? If not... I'm using the same module and having the same problem. Jump the resistors on the R and T pins on the module, they seem to be introducing high impedance on the line. After doing that on my module, the UART worked.

Now my problem now is the module is sending some weird characters, maybe my baud rate is not same or etc, still under investigation.

• Neko3: After further investigation, use shorter wires or connections between your module and arduino or mcu.

Answer 2

The SIM7600 UART interface works with 1.8 levels: enter image description here

I'm guessing that the AND board has a level shifter from 3.3 to 1.8 to work with the 7600. Since your Arduino Por Mini is a 5V board your UART levels must be at 5V too, try adding a voltage divider to bring down the UART to 3.3V.

Also try lowering the SIM7600 baudrate, the software_serial library doesn't work good with high speeds.

• Ashton: Did you ever get your Mini Pro to communicate with the SIM7600? I am now experiencing this using a SIM7600x core board(3.3v ttl). Other 5V MCUs work perfect (with level shifter) with the SIM7600, but using a 3.3V Pro Mini directly does not.