A LoRa briefing, and observations ( quite long )

Discussion in 'Arduino Playground' started by AD5MB, Apr 11, 2021.

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  1. AD5MB

    AD5MB Ham Member QRZ Page

    LoRa is a topic that has not come up often here. ergo, a brief discourse on LoRa, before getting to observations and conclusions.

    I have been grinding away at an Arduino project for years. It started out as a doorbell. then it became a doorbell with a clock and a datalogger. then it became a perimeter monitor for a large ( 10.0-12.5 acre, depending on who is saying ) property.

    and that's when it all fell apart, because how do you send motion sensor data a quarter mile across a gravel pit? the obvious answer is radio. the obvious answer is the ubiquitous 433 mhz Arduino RF module
    • aggravation #1: you would need one transmitter and one receiver per sensor. the property has more angles than Jimmy Durantes nose. expense and complexity in abundance. I briefly considered modifying CATV distribution amplifiers to feed the receivers
    • aggravation # 2: if you actually read Part 15, you will discover that all of the hordes of 433 mhz transceiver modules sold in this country are not legal in this country. we get 902 - 928 and the 2.4 ghz band here
    a major benefit of 915 mhz is LoRa - Long Range - invented by a French firm, Semtech. Semtech claims reliable communication at -148 dbm signal strength; below the noise floor. ( do your research before you argue. then, argue with someone else ). They claim reliable communications over 30 km between -20 dbm stations.

    there are two formats, LoRa and LoRaWAN. LoRaWAN is layers of complexity built on a LoRa foundation.

    LoRa is point to point, or multipoint to one Gateway.

    the LoRaWAN format is: many transmitters - thousands is possible - , a few LoRaWAN gateways, every gateway hears every transmitter in range, all the data is sent to certain major aggregators via the internet, the aggregators toss out duplicate packages, then send your data to a remote application server, which diddles your data and presents it to you in a manner of your choosing, and sends instructions back to your system.

    So: a weather station sensor detects rain, transmits this fascinating fact to a computer far away, which sends back a command to turn off your sprinklers. IF everything works right. I did mention layers of complexity.

    LoRa is the same thing, but you skip the requirement to encapsulate the data in a particular format ( JSON ), Send it through the ninnynet, , process it through a remote Application server, and get commands back. With LoRa, you do it all in house.

    legal 915 mHz Part 15 radios have many restrictions, or challenges, if you prefer. the radio is required to send brief packets of information. 250 byte packets, ten minutes apart, totaling 400 milliseconds per day, is stretching the envelope.

    the sending end is a node, or what hipster geeks call a mote, contraction of remote. LoRaWAN Gateways can be private, or open. if you have access to an open gateway, your personal expense is greatly reduced, but you have a thousand hoops to jump through.

    and here we get to the above mentioned observations. what I have learned, to spare you the aggravation and expense:

    You can't use a single channel gateway for LoRaWAN. You can set it up to use the system, but you can't open it up to the public. A public gateway must be 8 channels or more, capable of handling huge volumes of sensors and traffic. you can build a single channel gateway as a receiver for a LoRa node, and we are back to one receiver per transmitter complexity and expense.

    You can buy a single channel gateway for LoRa. it will cost $80 - $120, hear only some of your packets, because it's a frequency hopping system, and they just have a cobbled together look and feel.

    For $200, you can buy a full service RAK7243 or 7244. A RAK 2245 Concentrator on a Raspberry Pi. Single channel gateways have one SX1276 transceiver. A RAK 2245 Concentrator has two SX1301 quadrature phase transceivers, capable of receiving 8 channels. The first problem is that Raspberry Pis are poky little things, and LoRaWAN is very time sensitive. If you use an RPi to check Hotmail or eBay, you have experienced locking up. that just does not work in LoRaWAN

    The flow in a LoRaWAN gateway is: Antenna >> Transceivers >> Concentrator >> Packet Forwarder >> Network Server >> Application Server, then back through the same path. It would be trivially easy for the designer to make Concentrator out or Packet Fowarder out available. A LoRaWAN gateway could be a LoRa Gateway if they would provide the SPI out of the radio. or put one line in the Packet Forwarder code. In my experience, they just will not comprehend why you want it if you ask, and "It's my data, it's my Gateway, it's right there, and it could be coded during a coffee break" is not sufficient motive.

    if you have the material to construct a LoRa Node, you can also make a LoRa Gateway. It's the same hardware, you just run different software on it. so, don't waste half the cost of a RAK7243 on a single channel gateway, which you can build in half an hour on a TTGO ( brand name ) ESP32, for <$25.

    Don't waste your time and money on a Dragino LoRaHat ( for the RPi ) or LoraShield ( for an Arduino UNO or MEGA ) None of the software you find on the web works. The UNO does not have enough pins left to do anything worth while. The only thing I have found the LoRaShield good for is as a test signal source for a single channel gateway. To remain not far from legal, you have to operate it from a momentary contact pushbutton, run it just long enough to see the time and location on the gateway, and shut it down.

    The only thing I have found the LoRaShield good for is using it as a clay pigeon.

    I prefer the TTGO ESP32 with LoRa transceiver, OLED display ( useless if your eyes saw Howdy Doody in his prime ) and WiFi, because it has an SMA connector. I will not spend money on any radio that has a u.fl connector. If you get a TTGO ESP32, you need to know that the built in OLED uses different pins for the I2C connection than other brands of ESP32. TTGO uses Pin 4 for SCL and Pin 5 for SDA, versus the more common 20 and 21

    LoRa is all about: system wakes up, checks the status of its environment via sensors, sends out a brief packet, and goes back to sleep. when LoRa users get together, the big brag is "14 months on the same battery" that battery is an 18650: what a AA wants to be when it grows up. a AA would be leaking funky white powder after 14 months of very little use. 18650s are rechargeable, and each individual battery needs to be recharged at its own rate. the battery pack needs a BMS, a battery management system. batteries have their own learning curve in this world.
    WA9TDD and VE3CGA like this.
  2. WA9TDD

    WA9TDD Ham Member QRZ Page

  3. VE3CGA

    VE3CGA XML Subscriber QRZ Page

  4. K6CLS

    K6CLS Ham Member QRZ Page

    Great write up. LoRa seems compelling, until a close examination.

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