SIM808 GSM/GPRS + GPS Module
The SIM808 is a versatile GSM/GPRS module with integrated GPS functionality, providing quad-band connectivity for voice, SMS, data, and satellite navigation applications. Its compact design and multiple interfaces make it suitable for a wide range of communication and tracking projects.

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SIM808 pinout
The SIM808 pinout includes power, UART communication for GSM and GPS, control, status indication, dual antenna connections (cellular and GPS), and SIM card interface pins for quad-band GSM/GPRS and integrated GPS functionality.
| Pin | Type | Description | Notes |
|---|---|---|---|
| VBAT | Power | Power supply input (3.4V to 4.4V) | Requires stable power supply with peak current up to 2A |
| GND | Ground | Ground connection | Connect to common ground |
| TXD | UART TX | UART Transmit Data for GSM (connects to microcontroller RX) | Default baud rate: 9600 bps |
| RXD | UART RX | UART Receive Data for GSM (connects to microcontroller TX) | Default baud rate: 9600 bps |
| PWRKEY | Control | Power on/off control (active low) | Pull low for at least 1 second to power on |
| NETLIGHT | Status | Network status indication | LED indicator for network registration status |
| STATUS | Status | Module operating status indication | Shows module power state |
| GPS_VCC | Power | GPS power supply | Power supply for GPS module (3.3V) |
| GPS_TX | UART TX | GPS UART Transmit Data | GPS data output (NMEA sentences) |
| GPS_RX | UART RX | GPS UART Receive Data | GPS command input (optional) |
| ANT_GSM | Antenna | GSM antenna connection | Requires external GSM antenna |
| ANT_GPS | Antenna | GPS antenna connection | Requires external GPS antenna |
Quad-band GSM/GPRS module (850/900/1800/1900MHz) with integrated GPS
Supports voice calls, SMS, GPRS data transfer, and GPS location tracking
GPS supports up to 66 channels for satellite tracking
GPS sensitivity: -165dBm tracking, -147dBm acquisition
Dual UART interfaces: one for GSM, one for GPS
Requires SIM card for cellular connectivity
Power consumption: 2A peak during transmission
Default GSM UART baud rate: 9600 bps
Wiring the SIM808 to ESP32
Connect the SIM808 to your ESP32 via dual UART for AT command communication (GSM) and GPS data reception. The module requires a stable 3.4V-4.4V power supply with sufficient current capacity (peak 2A). External antennas are required for both GSM and GPS functionality.
| SIM808 pin | ESP32 pin | Purpose |
|---|---|---|
| VBAT | 3.7V-4.4V Power Supply | Provide stable power (NOT from ESP32 pin) |
| GND | GND | Common ground connection |
| TXD | GPIO16 (RX2) | SIM808 GSM TX to ESP32 RX |
| RXD | GPIO17 (TX2) | SIM808 GSM RX to ESP32 TX |
| GPS_VCC | 3.3V | GPS module power supply |
| GPS_TX | GPIO18 | GPS data output to ESP32 |
| GPS_RX | GPIO19 | GPS command input (optional) · optional |
| PWRKEY | GPIO4 | Power control (pull low to power on) · optional |
| ANT_GSM | External GSM Antenna | Connect GSM antenna |
| ANT_GPS | External GPS Antenna | Connect GPS antenna |
CRITICAL: Use a dedicated power supply (3.4V-4.4V, 2A peak) - DO NOT power from ESP32 pin!
Dual UART setup: one for GSM AT commands, one for GPS NMEA data
Default GSM UART baud rate is 9600 bps
GPS outputs NMEA sentences at 9600 bps
External GSM antenna is mandatory for network connectivity
External GPS antenna is mandatory for location tracking
GPS requires clear view of the sky for satellite acquisition
Pull PWRKEY low for at least 1 second to power on the module
Monitor NETLIGHT pin for network registration status
Insert active SIM card before powering on
GPS_VCC can be powered from ESP32 3.3V pin (low current)
Ensure good antenna placement for optimal signal reception
SIM808 code examples
SIM808 Arduino example
Copy#include <Arduino.h>
// Define ESP32 hardware serial port for SIM808
#define SIM808_TX 17 // ESP32 TX connected to SIM808 RX
#define SIM808_RX 16 // ESP32 RX connected to SIM808 TX
#define PWRKEY 4 // SIM808 Power Key pin (GPIO4, matches the wiring above)
// Initialize hardware serial for SIM808
HardwareSerial sim808(2);
void powerOnSIM808() {
pinMode(PWRKEY, OUTPUT);
digitalWrite(PWRKEY, LOW);
delay(1000); // PWRKEY must be held LOW for at least 1 second
digitalWrite(PWRKEY, HIGH);
delay(5000); // Wait for the module to initialize
}
void setup() {
Serial.begin(115200); // Serial Monitor
sim808.begin(9600, SERIAL_8N1, SIM808_RX, SIM808_TX); // SIM808 UART
powerOnSIM808();
Serial.println("Testing AT communication...");
// Test AT command
sendATCommand("AT");
// Set SMS text mode
sendATCommand("AT+CMGF=1");
// Send SMS
Serial.println("Sending SMS...");
sim808.println("AT+CMGS=\"+1234567890\""); // Replace with recipient's number
delay(1000);
sim808.print("Hello from ESP32 and SIM808");
sim808.write(26); // CTRL+Z to send
delay(5000);
printResponse();
}
void loop() {
// Add code to handle incoming messages or other functionalities
}
// Function to send an AT command and print response
void sendATCommand(const char *command) {
Serial.print("Sending: ");
Serial.println(command);
sim808.println(command);
delay(1000);
printResponse();
}
// Function to print response from SIM808
void printResponse() {
while (sim808.available()) {
Serial.write(sim808.read());
}
Serial.println("\n----------------------\n");
}This Arduino sketch interfaces with the SIM808 over the ESP32’s hardware serial (UART2) - more stable than SoftwareSerial and free of Serial Monitor conflicts. PWRKEY (GPIO9) powers the module on, then AT commands test communication (AT), switch to SMS text mode (AT+CMGF=1), and send a message (AT+CMGS). Wiring matches the diagram above: ESP32 TX GPIO17 to SIM808 RX, ESP32 RX GPIO16 to SIM808 TX, at 9600 baud. The same UART channel can be extended with GPS AT commands (AT+CGNSPWR=1, AT+CGNSINF) when you need position data.
SIM808 ESP-IDF example
Copy#include <stdio.h>
#include <string.h>
#include "driver/uart.h"
#include "driver/gpio.h"
#include "freertos/task.h"
#define TX_PIN 17
#define RX_PIN 16
#define PWRKEY_PIN 4
#define UART_PORT UART_NUM_1
#define GPS_UART_PORT UART_NUM_2
void init_uart() {
uart_config_t uart_config = {
.baud_rate = 9600,
.data_bits = UART_DATA_8_BITS,
.parity = UART_PARITY_DISABLE,
.stop_bits = UART_STOP_BITS_1,
.flow_ctrl = UART_HW_FLOWCTRL_DISABLE
};
uart_param_config(UART_PORT, &uart_config);
uart_set_pin(UART_PORT, TX_PIN, RX_PIN, UART_PIN_NO_CHANGE, UART_PIN_NO_CHANGE);
uart_driver_install(UART_PORT, 1024, 0, 0, NULL, 0);
}
void power_on_sim808() {
gpio_set_direction(PWRKEY_PIN, GPIO_MODE_OUTPUT);
gpio_set_level(PWRKEY_PIN, 0);
vTaskDelay(1000 / portTICK_PERIOD_MS); // Hold PWRKEY low for 1 second
gpio_set_level(PWRKEY_PIN, 1);
vTaskDelay(5000 / portTICK_PERIOD_MS); // Wait for the module to initialize
}
void app_main(void) {
init_uart();
power_on_sim808();
char *test_cmd = "AT\r\n";
uart_write_bytes(UART_PORT, test_cmd, strlen(test_cmd));
while (true) {
char data[128];
int len = uart_read_bytes(UART_PORT, data, sizeof(data), 100 / portTICK_PERIOD_MS);
if (len > 0) {
data[len] = '\0';
printf("Response: %s\n", data);
}
vTaskDelay(1000 / portTICK_PERIOD_MS);
}
}This ESP-IDF example initializes UART communication with the SIM808 module and powers it on using the PWRKEY pin (GPIO4). The UART interface is configured with GPIO17 as TX and GPIO16 as RX. An AT command is sent to test communication, and responses from the module are printed to the console. Additional UART configurations can be added for GPS functionality.
SIM808 ESPHome example
Copyuart:
tx_pin: GPIO17 # module RXD
rx_pin: GPIO16 # module TXD
baud_rate: 9600
# ESPHome's sim800l component speaks the generic SIM AT command set
sim800l:
on_sms_received:
- logger.log:
format: "Received '%s' from %s"
args: [ 'message.c_str()', 'sender.c_str()' ]ESPHome's sim800l component speaks the SIM800/SIM900 AT command set, which the SIM808 shares - the old custom-platform example no longer works (that component was removed from ESPHome in 2025). Wire UART2 as shown (9600 baud) and you get on_sms_received triggers plus sim800l.send_sms and USSD actions. Power the module from a supply that can deliver its transmit-burst current.
SIM808 PlatformIO example
Copy[env:sim808]
platform = espressif32
board = esp32dev
framework = arduino
monitor_speed = 115200#include <HardwareSerial.h>
#include <Arduino.h>
HardwareSerial sim808(1);
#define PWRKEY 4
void power_on_sim808() {
pinMode(PWRKEY, OUTPUT);
digitalWrite(PWRKEY, LOW);
delay(1000); // Hold PWRKEY low for 1 second
digitalWrite(PWRKEY, HIGH);
delay(5000); // Wait for initialization
}
void setup() {
Serial.begin(115200);
sim808.begin(9600, SERIAL_8N1, 16, 17); // RX, TX
power_on_sim808();
// Test AT command
sim808.println("AT");
delay(1000);
while (sim808.available()) {
Serial.write(sim808.read());
}
}
void loop() {
sim808.println("AT+CMGF=1"); // Set SMS to text mode
delay(1000);
sim808.println("AT+CMGS=\"+1234567890\""); // Replace with recipient's number
delay(1000);
sim808.print("Hello from PlatformIO");
delay(1000);
sim808.write(26); // CTRL+Z to send SMS
delay(5000);
}This PlatformIO code interfaces with the SIM808 module using HardwareSerial on an ESP32. The power_on_sim808 function toggles the PWRKEY pin (GPIO4) to activate the module. The AT command is sent to test communication, and SMS functionality is implemented in the loop. GPIO16 (RX) and GPIO17 (TX) are configured as serial pins.
SIM808 MicroPython example
Copyfrom machine import UART, Pin
import time
# Initialize UART
uart = UART(2, baudrate=9600, tx=17, rx=16)
pwrkey = Pin(4, Pin.OUT)
def power_on_sim808():
pwrkey.value(0)
time.sleep(1) # Hold PWRKEY low for 1 second
pwrkey.value(1)
time.sleep(5) # Wait for module to initialize
def send_at(command):
uart.write(command + '\r\n')
time.sleep(1)
while uart.any():
print(uart.read().decode('utf-8'), end='')
# Power on the module
power_on_sim808()
# Test communication
send_at('AT')
# Send SMS
send_at('AT+CMGF=1') # Set SMS to text mode
send_at('AT+CMGS="+1234567890"') # Replace with recipient's number
uart.write("Hello from MicroPython" + chr(26))This MicroPython code communicates with the SIM808 module over UART. The power_on_sim808 function activates the module using the PWRKEY pin (GPIO4). The send_at function sends AT commands and prints the responses. The script initializes the module, tests communication, and sends an SMS with a specified message. Additional logic can be added to read GPS data through UART.
SIM808 specifications
About the SIM808
The SIM808 pairs the same quad-band (850/900/1800/1900 MHz) GSM/GPRS engine used across the SIM800 family with an integrated GPS receiver in one 24 x 24 x 2.6 mm package - a 22-channel tracking / 66-channel acquisition receiver rated at -165 dBm tracking sensitivity, with a typical cold-start time-to-first-fix around 30 seconds. Cellular and GPS run over separate UARTs (GPS output is plain NMEA), so a project gets SMS, voice, GPRS data and a location fix from a single module and antenna pair - which is exactly why it shows up in so many budget vehicle and asset trackers, and why it needs both a GSM antenna and a separate GPS antenna wired up.
It inherits the same power behavior as the rest of the SIM800 line: a 3.4V to 4.4V supply that has to source multi-amp current bursts during transmission, not the ESP32’s 3.3V regulator. And it inherits the same 2G availability question, which by 2026 matters more than the quad-band radio does: US carriers have fully retired 2G (T-Mobile’s GSM network, the last one standing, closed on August 3, 2026), several EU carriers plan to keep limited 2G alive into the late 2020s or later for fallback and IoT use, and 2G in India remains commercially active with no announced end date as of 2026 - so whether a SIM808 tracker still works is a question about the deployment country, not the module.
TinyGSM lists SIM808 by name among its supported modems. If GNSS accuracy matters more than “some kind of GPS fix,” the newer SIM868 swaps the plain-GPS receiver for a multi-constellation GPS/GLONASS/BeiDou one in a notably smaller board; if 2G coverage is the actual risk, SIM7600G pairs LTE with the same kind of multi-constellation GNSS. For projects that only need SMS or GPRS with no positioning, SIM800L is the cheaper, simpler sibling.
SIM808 troubleshooting
Module Fails to Power On
›
Issue: The SIM808 module does not power up or respond to commands.
Possible causes include insufficient power supply, incorrect wiring, or faulty hardware.
Solution: Ensure the module is connected to a stable power source within the recommended voltage range of 3.4V to 4.4V. Verify that all connections are secure and correctly configured. If the problem persists, consider testing the module with a different power source or replacing it.
SIM Card Not Recognized
›
Issue: The module fails to detect or register the SIM card.
Possible causes include improper SIM card insertion, unsupported SIM card type, or SIM card lock.
Solution: Ensure the SIM card is properly inserted into the module's SIM card slot and is compatible with the GSM network. Verify that the SIM card is active and unlocked. If necessary, test the SIM card in another device to confirm its functionality.
Poor Network Signal or Connectivity Issues
›
Issue: The module experiences weak signal strength or fails to maintain a stable network connection.
Possible causes include improper antenna connection, environmental interference, or network coverage limitations.
Solution: Ensure the GSM antenna is securely connected to the module and positioned for optimal signal reception. Avoid placing the module near sources of electromagnetic interference. Check the network coverage in your area to ensure adequate signal strength.
AT Commands Not Responding
›
Issue: The module does not respond to AT commands sent from the microcontroller or computer.
Possible causes include incorrect baud rate settings, faulty serial connections, or improper command syntax.
Solution: Verify that the baud rate of the module matches that of the microcontroller or computer; the default baud rate is 9600 bps. Check that the TX and RX lines are correctly connected and that there are no loose connections. Ensure that AT commands are correctly formatted and terminated with a carriage return.
GPS Functionality Not Working
›
Issue: The SIM808 module fails to acquire GPS signals or provide location data.
Possible causes include improper antenna connection, obstructed view of the sky, or GPS functionality not enabled.
Solution: Ensure the GPS antenna is properly connected and has a clear view of the sky to receive satellite signals. Verify that the GPS functionality is enabled by sending the appropriate AT commands to power on the GPS engine.
Where to buy the SIM808

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