I'm trying to transmit from one ESP32 LoRa node to another one in low-power mode and in compliance with european regulations.
ESP32 board: TTGO LoRa32 OLED Board V1.0 (here and here).
Below the LoRa sender sketch I wrote:
/*
* LoRa (low-power) sender for IoT projects
*
* Tested on a TTGO LoRa32 OLED Board V1.0
*
* Based on the LoRa examples and the board
* documentation
*
* More on the deep sleep with timer wake up:
*
* Examples > ESP32 > Deep Sleep > TimerWakeUp sketch
*
*
* ERC Recommendation
* h1.4 frequency band requires <= 1% duty cycle and 25mW (14 db) maximum power
* => 36 seconds every hour (so: 1 sec transmitting, 99 secs idle)
*
*
* Created 11 June 2019
* by DP
*
*/
#include <SPI.h> // allows communication with SPI devices
#include <LoRa.h>
#include <SSD1306.h> // provides API to work with OLED displays
// defines the pins used by the transceiver module
#define SS 18 // GPIO18 - SX1278's CS - LoRa radio chip select
#define RST 14 // GPIO14 - SX1278's RESET - LoRa radio reset
#define DI0 26 // GPIO26 - SX1278's IRQ - IRQ pin
#define BAND 868E6 // EU - Italy
// deep sleep
#define uS_TO_S_FACTOR 1000000 // conversion factor for micro seconds to seconds
#define TIME_TO_SLEEP 5 // time ESP32 will go to sleep (in seconds) - 99 for (about) 1% duty cycle
// an object of class SSD1306
// first parameter: the I2C address of the display
// second parameter: the number of the SDA
// third parameter: the SCL pin
SSD1306 display(0x3c, 4, 15);
// stores the data on the RTC memory so that it will not be deleted during the deep sleep
RTC_DATA_ATTR int bootCount = 0;
RTC_DATA_ATTR int pckCounter = 0; // sending packet number...
void setup() {
Serial.begin(115200); // initializes serial data transmission
while(!Serial); // waits for serial port to connect
Serial.println("LoRa low-power Sender");
pinMode(16, OUTPUT);
digitalWrite(16, LOW); // sets GPIO16 low to reset the OLED
delay(50);
digitalWrite(16, HIGH); // while the OLED is running, GPIO16 must go to high
pinMode(2, OUTPUT);
digitalWrite(2, LOW); // sets the onboard LED low
// LoRa transceiver module setup
LoRa.setPins(SS, RST, DI0); // overrides the default CS, reset, and IRQ pins used by the library
// initializes the transceiver module with a specified frequency
while (!LoRa.begin(BAND)) { // LoRa.begin returns 1 on success, 0 on failure
Serial.println(".");
}
// changes the spreading factor to 12 -> slower speed but better noise immunity
LoRa.setSpreadingFactor(12); // ranges from 6-12, default is 7
// changes the sync word (0xF3) to match the receiver
// the sync word assures you don't get LoRa messages from other LoRa transceivers
LoRa.setSyncWord(0xF3); // ranges from 0-0xFF
// LoRa.setTxPower(txPower); // defaults to 17
// initializes the display by calling the init method of the display object
display.init(); // receives no arguments and returns void
// display.flipScreenVertically(); // LCD is broken!
display.setFont(ArialMT_Plain_16); // sets the current font
display.drawString(0, 0, "Initialization"); // x, y, message to show
display.drawString(0, 16, "completed");
display.display();
delay(1500); // small delay so that the user can read it
Serial.println("LoRa init completed");
//Increments boot number and prints it every reboot
bootCount++;
Serial.println("Boot number: " + String(bootCount));
sendData(); // sends the data...
// deep sleep
esp_sleep_enable_timer_wakeup(TIME_TO_SLEEP * uS_TO_S_FACTOR);
Serial.println("Setup ESP32 to sleep for every " + String(TIME_TO_SLEEP) + " Seconds");
Serial.println("Going to sleep now");
Serial.flush(); // waits for the transmission of outgoing serial data to complete
esp_deep_sleep_start(); // enters deep sleep with the configured wakeup options
}
void loop(){
// this is not going to be called
}
// sends the data to the receiver
void sendData() {
Serial.print("Sending packet: ");
Serial.println(pckCounter);
display.clear(); // clears the display
display.setTextAlignment(TEXT_ALIGN_LEFT);
display.drawString(0, 0, "Sending ");
display.drawString(0, 16, "packet: " + String(pckCounter, DEC));
display.display();
digitalWrite(2, HIGH); // LED is ON during transmission
// sends the LoRa packet to the receiver
LoRa.beginPacket();
LoRa.print("hello ");
LoRa.print(pckCounter);
LoRa.endPacket();
digitalWrite(2, LOW); // turns the LED off after transmission
pckCounter++;
}
The sketch runs without errors (the code on the shop's page contains some errors, so I encourage you to use this one just to play with it). My questions:
I forgot to initialize the SPI communication:
SPI.begin (SCK, MISO, MOSI, SS);But nevertheless, it worked anyway. I didn't expect it. My first question is: what am I missing?
I live in Europe. ERC Recommendation document says that h1.4 frequency band (I'm transmitting at 868 Mhz) requires <=1% duty cycle and 25mW (14db) maximum power. This means that I can transmit for 36 seconds every hour (let's say that I transmit for 1 sec and then the ESP32 'sleeps' for 99 seconds). I can achieve that writing (it's not the more accurate way but it should work):
#define TIME_TO_SLEEP 99What about the erp? Let's say that the antenna has a 2db gain, so I can set the transmission power to 12db (12db + 2db -> 14db, great. It's ok!):
LoRa.setTxPower(12);My second question: am I right (about both settings)? Am I missing something?
Last question: please, feel free to give me any (if you have) feedback/suggestion to improve this sketch!
