UART Communication between ESP32 and SIM800L EVB v2 module

Projects Networking, Protocols, and Devices
1

Below is my connection

TX -> GPIO 16 (RX)
RX -> GPIO 17 (TX)
VCC -> 5V 
GND -> GND

and my code is

#include <HardwareSerial.h>

HardwareSerial sim800(1);  // UART1

#define RXD2 16  // ESP32 RX ← SIM800 TX
#define TXD2 17  // ESP32 TX → SIM800 RX

unsigned long lastCheck = 0;

void setup() {
  Serial.begin(115200);
  sim800.begin(9600, SERIAL_8N1, RXD2, TXD2);

  Serial.println("SIM800 Communication Test Started");
}

void loop() {
  // Auto send AT every 3 sec
  if (millis() - lastCheck > 3000) {
    Serial.println("Sending: AT");
    sim800.println("AT");
    lastCheck = millis();
  }

  // Read from SIM800 → Serial Monitor
  while (sim800.available()) {
    char c = sim800.read();
    Serial.write(c);
  }

  // Send from Serial Monitor → SIM800
  while (Serial.available()) {
    char c = Serial.read();
    sim800.write(c);
  }
}

but i am not getting any response from the SIM800L module. I am using a dedicated 5V 2A external power supply for it and ESP32 is powered by USB, and have common GND. Why am I not receiving anything.

16:14:27.437 -> Sending: AT

16:14:30.442 -> Sending: AT

16:14:33.446 -> Sending: AT

16:14:36.420 -> Sending: AT

16:14:39.449 -> Sending: AT

16:14:42.461 -> Sending: AT

16:14:45.424 -> Sending: AT

16:14:48.435 -> Sending: AT

16:14:51.455 -> Sending: AT
2

From here: GitHub - SharmaAshmit/ESP32-SIM800L: This project demonstrates how to use the ESP32 with the SIM800L GSM/GPRS module to send sensor data (temperature & humidity) to Firebase Realtime Database using AT commands via serial communication. · GitHub

This:

Important: SIM800L requires a stable 4V power supply. Do not power it directly from ESP32 5V pin.

And this:

ESP32 Pin SIM800L Pin
GPIO 26 TX
GPIO 27 RX
GND GND
4V Power VCC
1 Like
3

I am using this module : SIM800L V2 5V GPRS GSM Module - Quad-Band with Antenna – QuartzComponents

image
image800×800 82.2 KB

image
image800×800 108 KB

I couldn't find the official datasheet of this board but i found this : https://ultra-lab.net/wp-content/uploads/2022/02/Ficha-tecnica-de-SIM800L-V2.0.pdf

Note : I am powering it via external source 5V 2A.

but still not getting any response of AT commands.

4
5

Bigger is not always better. Is it 5v tolerant?

Read the PDF you posted for power requirement.

6

try

// // SIM800L EVB ESP32 test using Serial2 (pins 16 Rx  and 17 Tx)

// connect so
// SIM800 5V to ESP32 5V
// SIM800 GND to ESP32 GND
// SIM800 VDD to ESP32 3.3v
// SIM80 TXD to ESP32 pin 16 Rx
// SIM800 TXD to ESP32 pin 17 tx

// AT+CGMI  returns the manufacturer's name
// AT+CGMM returns the MODEM model number
// AT+CGMR returns details of the software and model revision level
// AT+CGSN returns the MODEM's serial number

#include <Arduino.h>

// ESP32 example using HardwareSerial library to access Serial port 2 (pins 16 and 17)
// from https://programming.vip/docs/esp32-use-of-hardwareserial-library.html

#define SERIAL_BAUD 115200

HardwareSerial serial2(2);//Serial port 2

int distance = 0;

void setup() {
  //Initialize serial port 0
  Serial.begin(115200);
  delay(3000);
  //Initialize serial port 2
  serial2.begin(SERIAL_BAUD, SERIAL_8N1);
  Serial.println("\nSIM800 EVB to ESP32 Serial port 2 test");
}

void loop() {
  while (serial2.available() > 0) {
    uint8_t byteFromSerial = serial2.read();
    Serial.write(byteFromSerial);
  }
  while (Serial.available() > 0) {
    uint8_t byteFromSerial1 = Serial.read();
    serial2.write(byteFromSerial1);
  }
}

serial monitor output

at
OK
at+cgmi
SIMCOM_Ltd
OK
at+cgmm
SIMCOM_SIM800L
OK
at+cgmr
Revision:1418B05SIM800L24
OK

setup

image
image518×389 76.7 KB

for testing AT commands I used the ESP32 5V supply
when transmitting use an external 2amp supply