Teensy 4.0 with SIM800L - No Serial Comms

Other Hardware 3rd Party Boards
1

Hello,

I have got the basics working with an Arduino Nano, to communicate with a SIM800L module (EDIT: V2 SIM800L module). I can communicate with the SIM800L with the AT commands perfectly fine. No power issues with the SIM800L, all working fine with the Arduino Nano.

I have switched to the Teensy, because I want to use a Teensy and learn how to use it, and I cannot get the SIM800L working.

I have made the following connections:
SIM800L RX -> Teensy 4.0 Pin 7
SIM800L TX -> Teensy 4.0 Pin 8

I used this to determine the pins required:

Using the following basic code, that works with the Arduino Nano, I cannot get the Teensy to work. I have got the blink code working on the Teensy, so I assume it is not an issue with the Teensy. Most likely it is an issue with my code or understanding of how the Teensy is slightly different. Please could anyone help?

#define SIM800L Serial2        //RX is pin 7, TX is pin 8.

void setup() {
  // Begin serial communication with Arduino and Arduino IDE (Serial Monitor)
  Serial.begin(9600);
  
  // Begin serial communication with SIM800L
  SIM800L.begin(9600);
  SIM800L.println("AT");
  delay(100);
}

void loop() {
  // If there's any serial available, read it and send it out
  // SIM800L's UART (Serial Monitor)
  if (Serial.available()) {
    SIM800L.write(Serial.read());
  }
  // If there's any serial available from SIM800L, read it and send it out
  // through Arduino's UART (Serial Monitor)
  if (SIM800L.available()) {
    Serial.write(SIM800L.read());
  }
}
2

What is the power supply that you're using?

3

I should have stated, I am using the SIM800L V2 module.

I have the Teensy connected to the PC via USB. The SIM800L is supplied by a converter capable of supplying the 5V, 2A. The ground of the SIM800L is tied to the ground on the Teensy.

This is the exact same setup I had with the Arduino Nano, which I had working perfectly fine - no power supply issues, of which I am aware of due to a lot of people having issues with it.

4

It appears at first glance that you have RX connected to RX (T4.0 pin 7) and XX(TX?) connected to TX (T4.0 pin 8).

5

I had an initial thought that they were not the correct way around, but I managed to convince myself it was right...

You were correct kind person... I had TX and RX the wrong way around. Most helpful, thank you also for the way you presented your feedback. Fixed.