1. Input voltage range: 5V–18V DC. 2. Self-ejecting SIM card slot supports standard mini-SIM cards. The module powers on and establishes network connection automatically upon power application—no manual activation required. 3. User-controllable power on/off functionality. Direct startup upon power-up, with a dedicated power-on pin reserved for external control. 4. Integrated TTL-level serial interface, compatible with common microcontroller UART ports—no level-shifting circuitry required. 5. Audio interface with reserved headphone and microphone connectors for easy testing. Supports TTS (Text-to-Speech) and DTMF (Dual-Tone Multi-Frequency) functions for voice playback and keypad signal detection during calls. Bluetooth 3.0 compliant, featuring an enhanced antenna for improved signal performance; supports SPP (Serial Port Profile) and audio streaming. Reserved BAT port for external lithium-ion battery power supply (e.g., 3.7V or 18650 cells—not included). Reserved D-type connector, SMA connector, and spring antenna connector for flexible antenna options. Status LED indicator: Flashes once per second when no network is detected, no SIM is present, or the SIM is improperly inserted; flashes once every three seconds when successfully connected to the network. Color: As shown in product images. Material: Plastic + metal. Package Contents: 1 × Development Board 2 × Pin Headers 1 × Antenna Note: Actual product color may vary slightly due to lighting conditions and display settings. Dimensions are subject to a tolerance of ±1–3 cm.