Arduino and wireless network LoRa (long range)

Table of Contents

• Preface
• What is a MiniReteLoRa and what is it for?
• Why should I choose a MiniReteLoRa?
• How do you make it?
• Hardware
• The board: LILYGO TTGO T-Deer Pro Mini, as a sensor node
• The board: LILYGO TTGO LoRa32 T3_V1.6.1 (LoRa32 V2.1_1.6), as RX node
• The board : LILYGO TTGO LORA32 868/915Mhz (LoRa32 V1.0), as RX node
• Software
• The structure of the sent message
• The program for a generic TX node: TX_Generic
• The program for the receiving node RX_Generic_autoconnect
• RSSI signal level and antennas
• Libraries
• Data Platform
• RX Node Operation
• Reliability test of a MiniReteLoRa
• Conclusions

Preface

What is a MiniReteLoRa and what is it for?

Let's start with some examples of practical applications:

• in a cultivated field there is the need to measure the temperature of the air and the ground, the water content in the soil and so on, but we are far from a house with WiFi and electric energy;
• still in the countryside, we have to control a pump to lift water from a well and fill a tank when it is about to empty, but this is located quite far away; we also want the pump to turn on automatically and follow the operation of the whole system on the Internet;
• we have a greenhouse where it is important to keep the air temperature under control at various points to manage the heating systems or the opening of the air vents, but we don't want to put a lot of electric wires in the middle of the plants;
• we want to install on a hill a small network of rain gauges and vibration sensors to alert the population of a small village in the event of a flood or landslide;

Monitoring air and water quality can help to prevent environmental disasters alerting people when the level of pollutants is too high
All of these applications require sensors, data acquisition and transmission electronics, and a receiver node located far away.
What system can be used to transmit the data? The GSM-4G network? A WiFi network? In the first case we would have to pay a fee and equip each sensor-card with a SIM with an energy consumption that does not allow us to power the node with a battery for months; in the second case we would need sensor-boards equipped with WiFi, again with a non-negligible battery consumption and a WiFi/GSM router for Internet with a coverage that could not exceed 300-600 ft (100-200 mt.)

For some years a new transmission technology has become available with the relative Hw and Sw: it is LoRa (Long Range). The acronym indicates a radio signal modulation technique which allows for great sensitivity at the receiving point, resulting in a coverage of kilometers, as the name implies, with the transmitter's output power reduced to a minimum and short transmission times for each sensor-board.
LoRa, in Europe, uses the free 868 MHz (915 MHz in USA) band provided you don't occupy it for more than 1% of the time. Imagine a sensor that transmits small quantity of data every 5 minutes with a transmission time of 70 ms (milliseconds), the bandwidth occupation percentage is about 0.02% which would allow us to have up to 50 sensor boards scattered everywhere!!
The typical consumption of a sensor board is 140 mA in transmission and 0.30 mA at rest, (with the CPU in sleep), therefore the average consumption, always for the same example, is 0.32mA. In these evaluations I have not taken into account the consumption of the sensors, which in any case can be negligible if these are activated only shortly before the transmission of their data.
The egg of Columbus for our needs?
Yes, but what difficulties are encountered in building such a network? Is there something turnkey on the market? Do you have to be super expert in Hw/Sw?
Here the world of open source helps us: that universe of knowledge available on the Net, free and often made easy by skilled disseminators. In addition, there is a low-cost hardware market that is expanding more and more, offering us sensors, microcontrollers and easy-to-wire solutions. If we are already able to connect a sensor to a microcontroller like Arduino, we can with little effort enter the world of the Internet of Things (IOT) that uses LoRa and build our own MiniReteLoRa.
Now I will try to describe the architecture of what I call MiniReteLoRa (literally in english mini network LoRa), a completely autonomous network of sensors-transmitters and concentrator-receiver, which does not need to rely on particular external servers and submit to complex protocols.