The **NL-AB-RPI** is a specific development board designed by NimbeLink (now part of Airgain). It is better known as the **Skywire® Raspberry Pi Adapter**. This board acts as a bridge between the Raspberry Pi’s GPIO header and Skywire cellular modems. --- ### 1. Key Electronic Components & Subsystems | Component | Description | | :--- | :--- | | **Skywire Interface** | A 20-pin dual-row socket designed to hold any NimbeLink Skywire cellular modem (LTE-M, NB-IoT, or 4G LTE). | | **GPIO Header** | A standard 40-pin female header that mounts directly onto the Raspberry Pi (compatible with 3B, 4B, and Zero). | | **Power Supply (Buck Regulator)** | Converts the Raspberry Pi's 5V rail to a stable 3.8V - 4V required by cellular modems, handling high current spikes during transmission. | | **Level Shifters** | Onboard circuitry that translates logic levels between the Raspberry Pi (3.3V) and the Skywire modem (typically 1.8V or 3.3V). | | **SIM Card Slot** | A standard Micro-SIM (3FF) slot used to provide cellular identity to the mounted modem. | | **USB Interface** | A Micro-USB port that allows the modem to communicate via high-speed USB instead of just the UART pins. | --- ### 2. Communication Interfaces The NL-AB-RPI utilizes three primary methods to connect the Pi to the cellular network: 1. **UART (Serial):** Uses the Pi's TX/RX pins. This is the simplest method for sending AT commands but has lower data throughput. 2. **USB Path:** By connecting a cable from the adapter's Micro-USB port to the Pi's USB port, you can achieve high-speed data transfers (essential for 4G/LTE). 3. **I2C/SPI:** The board routes these pins through the header, allowing the modem to interact with secondary sensors if the specific modem firmware supports it. --- ### 3. Technical Specifications | Parameter | Specification | | :--- | :--- | | **Input Voltage** | 5V DC (via Raspberry Pi GPIO) | | **Operating Voltage** | 3.3V (I/O) / 3.8V (Modem Core) | | **Form Factor** | Raspberry Pi HAT (Hardware Attached on Top) compatible | | **Antenna Ports** | Provided via the Skywire Modem (U.FL connectors) | --- ### 4. Implementation Example (Python) To check the connection to the electronic hardware via the Serial port, you can use the following code: ```python import serial import time # Initialize serial connection to the NL-AB-RPI # Default Pi UART is /dev/ttyS0 or /dev/ttyAMA0 ser = serial.Serial("/dev/ttyS0", 115200, timeout=1) def check_modem(): ser.write(b'AT\r') # Send Attention command response = ser.read(64) print(f"Modem Response: {response.decode()}") check_modem() ``` ---