Comparing 4G and WiFi Modules

4G modules require a SIM card with active data plan to establish internet connectivity, similar to mobile devices. WiFi modules connect through existing router networks.

Key differences:

• 4G modules provide mboility with cellular coverage
• WiFi requires fixed infrastructure
• Both require valid credentials (SIM data plan for 4G, WiFi password for routers)

Hardware Setup

Module Initialization

Essential AT commands (include \r\n termination):

• ATE1 - Enable command echo
• AT+CPIN? - Verify SIM card presence
• AT+CREG? - Check network registration
• AT+CSQ - Signal strength indicator
• AT+CGSN - Retrieve device IMEI

/**
 * @brief Verify EC20 module readiness
 * @return EC20_OK if initialization succeeds
 */
uint8_t check_module_status() {
    char signal_strength[BUFFER_SIZE] = {0};
    
    // Basic communication test
    if(!send_at_command("AT", "OK", 150)) {
        if(!send_at_command("AT", "OK", 200)) {
            return COMM_FAILURE;
        }
    }
    
    if(!send_at_command("ATE1", "OK", 150)) {
        return COMM_FAILURE;
    }
    
    if(!send_at_command("AT+CPIN?", "READY", 150)) {
        return SIM_MISSING;
    }
    
    // Network registration check
    char* reg_status = get_response_buffer();
    if(!send_at_command("AT+CREG?", "2,1", 150)) {
        if(!strstr(reg_status, "0,1") && !strstr(reg_status, "0,5")) {
            if(send_at_command("AT+CSQ", "OK", 200)) {
                strncpy(signal_strength, reg_status+15, 2);
            }
            return NETWORK_FAILURE;
        }
    }
    
    if(!send_at_command("AT+CGSN", "OK", 150)) {
        return IMEI_ERROR;
    }
    
    store_imei(reg_status+10);
    return EC20_OK;
}

MQTT Connection Setup

// Establish MQTT connection sequence
int setup_mqtt_connection() {
    if(!send_at_command("AT+CGATT?", ": 1", 140)) return 1;
    if(!send_at_command("AT+QIACT?", "OK", 100)) return 2;
    if(!send_at_command("AT+QIDEACT=1", "OK", 120)) return 3;
    
    // MQTT configuration
    if(!send_at_command("AT+QMTCFG=\"recv/mode\",0,0,1", "OK", 250)) return 12;
    
    char cmd_buffer[BUFFER_SIZE];
    snprintf(cmd_buffer, sizeof(cmd_buffer), 
             "AT+QMTOPEN=0,\"%s\",%d", 
             mqtt_server, mqtt_port);
    if(!send_at_command(cmd_buffer, "+QMTOPEN: 0,0", 1500)) return 13;
    
    snprintf(cmd_buffer, sizeof(cmd_buffer),
             "AT+QMTCONN=0,\"%s\",\"%s\",\"%s\"",
             client_id, username, password);
    if(!send_at_command(cmd_buffer, "+QMTCONN: 0,0,0", 250)) return 14;
    
    return 0;
}

Troubleshooting

Common connectivity issues:

1. No Data Plan:

   • Verify SIM with AT+QCCID
   • Check AT+CREG? response (0,0 or 0,3 indicates issues)
   • AT+CGATT? returning 0 means no network connection

2. Performance Factors:

   • Antenna positioning (optimal outdoor placement)
   • Cellular tower proximity
   • Debugger interference (disconnect SWD during operation)
   • Command timing (adjust based on empirical testing)

Useful AT Commands

Location Tracking:

AT+COPS=3,2
AT+COPS?
AT+CREG=2
AT+CREG?

SMS Operations:

AT+CMGF=1
AT+CMGS="phone_number"
message_content
Ctrl+Z (0x1A)

Time Synchronization:

AT+QLTS=2