HopeRF RFM95W-915S2R LoRa Module

The RFM95W module communicates via a standard 4-wire SPI interface (MOSI, MISO, SCK, NSS/CS). You must connect these pins to your host microcontroller's SPI peripheral, ensuring the NSS pin is configured as a GPIO output for chip selection. Additionally, connect the RESET and DIO0-DIO5 pins as needed for interrupt-driven operation and hardware reset. Proper power supply decoupling with a 1uF and 100nF capacitor near the module's VCC pin is critical for stable RF performance.

Configuration is performed via SPI register writes. First, put the module in Sleep mode, then set the OpMode register to LoRa mode. Key parameters like carrier frequency (set for 915 MHz), spreading factor (SF7 to SF12), bandwidth (125 kHz, 250 kHz, etc.), and coding rate are written to specific registers (e.g., Frf, ModemConfig1/2/3). Use established libraries like RadioLib or the Semtech reference driver to simplify this process. Always calibrate the RC oscillator and perform a full calibration sequence after initial power-up or frequency changes.

Current consumption varies with output power and mode. In transmit mode at +14 dBm output, expect approximately 85-100 mA peak current. In continuous receive (Rx Single) mode, consumption is around 10-12 mA. For lowest power, use Sleep mode, where the core shuts down but SPI registers are retained, drawing about 200 nA. To achieve microamp-level sleep, you can physically power down the module using a MOSFET switch, as the deep sleep current with power applied is in the range of 1-2 uA.

Use a 915 MHz antenna with a 50-ohm impedance, such as a quarter-wave whip or PCB trace antenna. The module's RF output is designed for 50 ohms. For optimal performance, keep the antenna feed line as short as possible. If using a cable, ensure it is 50-ohm RF coaxial (like RG174). A matching network (typically an LC pi-network) may be required between the module's RF pad and the antenna connector to fine-tune return loss (VSWR), which can be designed using an RF simulator or a vector network analyzer for best efficiency.