1. Input voltage range: 5V–18V DC. 2. Self-ejecting SIM card slot accepts standard mini-SIM cards. The module automatically powers on and establishes network connection upon power application, eliminating manual activation. 3. User-controlled power on/off functionality. Direct startup upon power-up; includes a reserved power-on pin. 4. Integrated TTL level conversion circuitry ensures compatibility with various microcontroller UART interfaces. Direct connection without additional level-shifting required. 5. o interface with dedicated pins for headphone and microphone connections. Supports TTS (Text-to-Speech) and DTMF (Dual-Tone Multi-Frequency) functions for voice playback and keypad input during calls. 6. Bluetooth 3.0 compliant with enhanced antenna design for improved signal performance. Supports SPP (Serial Port Profile) and o streaming. 7. Reserved BAT port supports external 3.7V lithium-ion battery or 18650 battery (battery not included). 8. Reserved connectors include D-type, SMA, and spring antenna interfaces to accommodate various antenna options. 9. Operating status LED indicator: flashes once per second when no network is detected, no SIM card is present, or the SIM card is improperly inserted; flashes once every three seconds when successfully connected to the network. 10. Color: As shown in image 11. Material: Plastic + Metal 12. Package Contents:   1 × Development Board   2 × Pin Header Strip   1 × Antenna 13. Note: Color appearance may vary slightly due to lighting conditions and display settings. Dimensional tolerance: ±1–3 cm.