LoRa

What is LoRa?

LoRa (Long Range) is a spread spectrum modulation technique derived from chirp spread spectrum (CSS) technology and is the first low-cost implementation of chirp spread spectrum for commercial usage.^[1] It was developed by Cycleo of Grenoble, France, and acquired by Semtech in 2012, a founding member of the LoRa Alliance.(Wikipedia).

What do I want to do?

We have a Washing Machine in the basement - and allways forget when its finished. So I want to build a LoRa module, stick it to the Washing Machine.  A little sensor will check when it runs (by the movement). And when its finishing running (tumbling) - it will  notify me with OpenHab.  Aaah.. yes - and we have a garage (only 1 for 2 cars). So,  how to know, if its already used by one car. Also an idea for LoRa.

Network Topology

LoRa consists of 4 parts:

1. Nodes: Endpoint, e.g. measuring device
2. Gateways: Bridge between the note and the internet, the number of channels that a gateway has is the number of nodes that it can talk to at once, node is not sending allays, e.g. a 1% duty cycle represents almost 15 minutes of combined
3. Network Servers: direct packets between gateways and application servers. Since LoRaWAN™ allows for uplinks (messages to a server from a node) and downlinks (messages to a node from a server).
4. Application Servers: Does actually do something with the data.

I will try first to get a P2P communication running, meaning just connecting 2 LoRa Endpoints calling Client and Server

Client and Server

As the "LoRa Server" I plan to use an ESP8266 (with WIFI) - to connect to RFM95.

As the Client I want to use a module (ready made) you can by in china for cheap money: LoRa Radio Node v1.0.

For both I will use the the LoRa-Library from Sandeepmistry.

Server: ESP8266 with RFM95

The RFM95 Device

1. Frequency used in Germany: Frequency Plan: EU863-870, 868 Mhz,  you must use at least the 3 main channels you already mentioned (868.1, 868.3 & 868.5) with a duty cycle of <1%
2. Device used: RFM95 868 MHz (my one does not have a "W" - RFM95 vs RFM95w)
3. Antenna:cut a stranded or solid core wire the the proper length for the module/frequency: 868 MHz - 3.25 inches or 8.2 cm ((How to connect the antenna)

These different transceivers are using Semtech SX1276 chip.

The configuration and communication of the module is done via 4-wire SPI Bus, technically implemented in all microcontrollers.

RFM95 Documentation

1. ANT is the antenna Pin.
2. GND can be connected to any of the GND pad (connecting all is always better)
3. DIO0 is used by RFM95w module to trigger RxDone/TxDone status.
4. DIO1 is used by RFM95w module to trigger RxTimeout and other kind of errors status.
5. NSS, MOSI, MISO, SCLK are for SPI communication. NSS is the chip select signal. Arduino is the master.
6. Reset is resetting the RFM95w module.

Wiring

see gallery below for mapping RFM95 with ESP.

Serial interface and  does not work, when pin 2 is connected. Pin can be connected after serial starts working.

Client with LoRa Radio Nove v1.0

As "LoRa Client (the module that is sending data, form a sensor) I am using the  LoRa Radio Node v1.0

1. Power supply: 3.7V 14500 Lipo battery Or 3.7-12V DC power(VCC GND: 2PIN 2510-I Type connect) and 3.3V regulator with 500mA peak current output
2. ATmega328P @ 8MHz with 3.3V logic/power, 32K of flash and 2K of RAM, same usage as Arduino pro mini.
3. Hardware Serial, hardware I2C, hardware SPI support
4. 1 x PWM pins: D3
5. 2 x analog inputs: A0 A1
6. Pin #13 BLUE LED for general purpose blinking
7. Reset button

Wiring

Nothing to wire at all. Connect Antenna, put in a 3.7V LiI-Ion Battery (e.g. Model 17500, 3.7V,850mAH) for operation and use a standard FTDI cable to program and test.

Pin Mapping between RFM95 and ATmega328P:

RFM_DIO0 = 2
RFM_NSS  = 10
RFM_RESET 9

The ATMega and the RFM95 will be sent to Deep-Sleep to save power. Wake-up is possible via connecting RESET to GND.

First Results

Distance:  Amazing, 3 level building with thick walls down into the cellar - still working.  RSSI values from -23 (when close to together, down-to -99 on some distance). I am impressed by LoRa technology. It works for my use-case 🙂

Power-Consumption - Sending: A lot when sending - but only on peek times.

Power-Consumption - Sleeping: Using DeepSleep Library and sending the RFM95 via LoRa.sleep results in  0.08mA to 0.1mA, providing nearly a year of runtime with a 850mAh battery. Perfect