The SIM800C is a quad-band GSM/GPRS module made by SIMCom. It allows microcontrollers like NodeMCU ESP8266/ Arduino uno/Nano,... to connect to mobile networks to make calls, send SMS, or access the internet (GPRS data).
Feature
Details
GSM Bands
850/900/1800/1900 MHz (works almost worldwide)
Network Services
Voice, SMS, GPRS (Internet)
Supply Voltage
3.4V – 4.4V (recommended 4.0V)
Interfaces
UART (Serial Communication), Audio, I2C, GPIO
AT Commands
Used for controlling the module
Data Speed (GPRS)
Up to 85.6 kbps (download) / 42.8 kbps (upload)
Size
Very small (17.6 × 15.7 × 2.3 mm)
 
 How It Works (Basics)
 
Connect SIM800C to NodeMCU via UART (Serial).
Use AT commands to:
Check network
Make calls
Send and receive SMS
Connect to the internet via GPRS
 
Simple NodeMCU + SIM800C Code Example (Send SMS
 
 
#include <SoftwareSerial.h>
SoftwareSerial sim800(5, 4); // (RX, TX)
void setup() {
  Serial.begin(9600);
  sim800.begin(9600);
  
  Serial.println("Sending SMS...");
  sim800.println("AT"); 
  delay(100);
  sim800.println("AT+CMGF=1"); // Set SMS to Text Mode
  delay(100);
  sim800.println("AT+CMGS=\"+1234567890\""); // Replace with your phone number
  delay(100);
  sim800.print("Hello from NodeMCU!");
  delay(100);
  sim800.write(26); // ASCII code of CTRL+Z to send SMS
}
void loop() {
  // Nothing to do here
}