RFM95W-915S2 Development Board

This repository contains the design of a development board for the RFM95W-915S2. The PCB was designed using KiCad.

The RFM95W-915S2 Development board is a PCB that contains a RFM95W LoRa transceiver, a U.FL connector for the external antenna, a decoupling capacitor and a group of headers connected to the different pins of the transceiver. The transceiver can be used as a sender or a receiver.

Context

This is one of the breakout boards made for the EJA "Intelligent Popup Buoy" project (2021 Hackaday Dream Team). LoRa is how the buoy reports its position to a surface gateway, so the RFM95W was proved out on this board before being placed on the EJA M board and the Onboard Gateway. The board is intentionally minimal: transceiver, U.FL antenna connector, one decoupling capacitor, and every useful pin on 2.54 mm headers.

Table of Contents

1. Schematic
2. Bill of Materials
3. 3D Model
4. Firmware and Testing
5. Repository Layout
6. Authors

Schematic

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Bill of Materials

Reference	Quantity
RFM95W-915S2 LoRa™ Transceiver Module 915MHz SMD	1
10 µF ±10% 6.3V Ceramic Capacitor 0805	1
U.FL (UMCC) Connector Receptacle, Male Pin 50 Ohm SMD	1
Conn Header 40POS 2.54	1

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3D Model

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Firmware and Testing

The webpage randomnerdtutorials.com has an amazing tutorial named ESP32 with LoRa using Arduino IDE – Getting Started, that tutorial contains detailed information about how to use the RFM95 with an ESP32 (the same microcontroller that was selected for our designs). I used the same firmware and connections provided by the tutorial.

The test requires 2 transceivers, one of them will be used as a sender and the other as a receiver. In this case, one of the transceivers is the RFM95W-915S2 Development board and the other one is the RFM95W transceiver from Adafruit.

The connections are the following:

ESP32	RFM95W-915S2 Development Board
3V3	3.3V
GND	GND
GPIO 14	RST
GPIO 5	CS
GPIO 18	SCK
GPIO 23	MOSI
GPIO 19	MISO

ESP32	RFM95W Board from Adafruit
3V3	VIN
GND	GND
GPIO 14	RST
GPIO 5	CS
GPIO 18	SCK
GPIO 23	MOSI
GPIO 19	MISO

This repository contains a folder named /Firmware/ that contains the project for the transceiver as a receiver and a sender.

Both of the RFM95W Boards were used as a sender and receiver, the result was successful in both cases. During the test, one of the transceivers sends the package "hello counter", where the counter is a number that goes from 0 to 32767. The other transceiver receives the package and prints the message through serial.

Before you flash:

• The sketches call LoRa.begin(915E6) to match the RFM95W‑915S2 (915 MHz) module fitted to this board. If you pair it with a module for another band, change that argument (433E6 Asia, 866E6 Europe).
• The sender and receiver must use the same sync word (LoRa.setSyncWord(0xF3)) or they will ignore each other.
• Pin map used by both sketches: NSS/CS → GPIO5, RST → GPIO14, DIO0 → GPIO2, and hardware SPI (SCK GPIO18, MOSI GPIO23, MISO GPIO19).

Requisites

1. ESP32 Add-on in Arduino IDE
2. LoRa Library

Results visualized in the serial monitor from the receiver circuit:

For more information about the firmware visit the original tutorial for the RFM95W.

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Repository Layout

README.md
LICENSE                              Apache 2.0
Schematic v1.0.pdf                   exported schematic
Images/                              schematic, 3D renders, board/antenna photos, test result
Firmware/
  esp32_RFM95_sender/                Arduino sketch, sender
  esp32_RFM95_receiver/              Arduino sketch, receiver
lora-testing-board/                  KiCad project
  lora-testing-board.pro/.sch/.kicad_pcb
  lora-testing-board.csv             BOM
  Symbols/ Footprints/ 3D/           project-local libraries
  Gerber/                            fabrication output
  Exports/                           STEP model

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Authors

• Leonardo Ward

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