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This corrects the final lesson to use legal 915mHz radio frequency. Also updates it to use GPS coordinates as the payload. Adds another ino for a heltec v3 lora radio and u-blox GPS that can support high altitude flight #19

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This corrects the final lesson to use legal 915mHz radio frequency. Also updates it to use GPS coordinates as the payload. Adds another ino for a heltec v3 lora radio and u-blox GPS that can support high altitude flight #19

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ee6b5d0
Add Lesson 7 Heltec V3 GPS and SD Card example
snarfattack Mar 29, 2026
d0fa5c1
Refactor LoRa setup and improve data display
snarfattack Mar 29, 2026
18134a9
Refactor GPS and LoRa functionality in transmitter code
snarfattack Mar 29, 2026
d7c827a
Refactor receiver code for improved readability
snarfattack Mar 29, 2026
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187 changes: 187 additions & 0 deletions telemetry/esp32-heltec-tracker/c/lesson-7/Lesson_7_Heltec_V3_U-BloxGPS_SD-card.ino
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#include <RadioLib.h>
#include <TinyGPS++.h> // Mikal Hart v1.0.3
#include <SD.h>
#include <SPI.h>
#include <Wire.h>
#include <Adafruit_GFX.h>
#include <Adafruit_SSD1306.h>

// Heltec V3 Internal Pins
#define VEXT_PIN 36
#define OLED_RST 21
#define LORA_NSS 8
#define LORA_DIO1 14
#define LORA_NRST 12
#define LORA_BUSY 13

// SD Card Pins - Using separate HSPI bus
#define SD_CS 7
#define SD_SCK 4
#define SD_MISO 5
#define SD_MOSI 6

SPIClass hspi(HSPI);
SX1262 lora = new Module(LORA_NSS, LORA_DIO1, LORA_NRST, LORA_BUSY);
TinyGPSPlus gps;
HardwareSerial SerialGPS(2);
Adafruit_SSD1306 display(128, 64, &Wire, OLED_RST);

volatile bool txBusy = false;
unsigned long lastActionTime = 0;
bool sdEnabled = false;

// Interrupt for non-blocking LoRa transmission
void onTxDone(void) {
txBusy = false;
}

// Function to handle SD Mounting and Recovery
void trySDInit() {
if (SD.begin(SD_CS, hspi, 4000000)) {
sdEnabled = true;
File file = SD.open("/flight.csv", FILE_APPEND);
if(file) {
file.println("--- LOG SESSION START ---");
file.println("DATE,TIME,LAT,LON,ALT_FT,SATS");
file.close();
}
} else {
sdEnabled = false;
}
}

void setup() {
Serial.begin(115200);

// 1. Hardware Power/Reset
pinMode(VEXT_PIN, OUTPUT);
digitalWrite(VEXT_PIN, LOW);
pinMode(OLED_RST, OUTPUT);
digitalWrite(OLED_RST, LOW); delay(50); digitalWrite(OLED_RST, HIGH);

// 2. Initialize OLED
Wire.begin(17, 18);
display.begin(SSD1306_SWITCHCAPVCC, 0x3C);
display.clearDisplay();
display.setTextColor(WHITE);
display.setCursor(0,0);
display.println("BALLOON SYSTEM BOOT");
display.display();

// 3. Initialize SD (HSPI Bus)
hspi.begin(SD_SCK, SD_MISO, SD_MOSI, SD_CS);
trySDInit();
display.println(sdEnabled ? "SD: READY" : "SD: NOT FOUND");
display.display();

// 4. Initialize GPS
SerialGPS.begin(9600, SERIAL_8N1, 45, 46);
// UBX Airborne < 1g Mode Command
byte packet[] = {0xB5, 0x62, 0x06, 0x24, 0x24, 0x00, 0xFF, 0xFF, 0x06, 0x03, 0x00, 0x00, 0x00, 0x00, 0x10, 0x27, 0x00, 0x00, 0x05, 0x00, 0xFA, 0x00, 0xFA, 0x00, 0x64, 0x00, 0x2C, 0x01, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x16, 0xDC};
SerialGPS.write(packet, sizeof(packet));
display.println("GPS: AIRBORNE SET");
display.display();

// 5. Initialize LoRa
// freq: 915.0, bw: 125.0, sf: 7, cr: 5, sync: 0x12, pwr: 10, preamble: 8, tcxo: 1.6V, LDO: false (DC-DC)
int status = lora.begin(915.0, 125.0, 7, 5, 0x12, 10, 8, 1.6, false);
if (status == RADIOLIB_ERR_NONE) {
display.print("LORA PING... ");
display.display();

// Blocking startup ping
int txStatus = lora.transmit("BALLOON_ONLINE_STARTUP");

if(txStatus == RADIOLIB_ERR_NONE) display.println("SENT");
else display.println("FAIL");

lora.setPacketSentAction(onTxDone);
} else {
display.printf("LORA ERR: %d\n", status);
}
display.display();
delay(2000);
}

void loop() {
// Constant GPS Feeding
while (SerialGPS.available() > 0) {
gps.encode(SerialGPS.read());
}

// Action Cycle: 10 Seconds
if (millis() - lastActionTime > 10000) {

// A. SD Recovery Check
if (!sdEnabled) {
trySDInit();
}

// B. Build Data String
char dataBuf[128];
snprintf(dataBuf, sizeof(dataBuf), "%02d/%02d/%d,%02d:%02d:%02d,%.6f,%.6f,%.1f,%d",
gps.date.month(), gps.date.day(), gps.date.year(),
gps.time.hour(), gps.time.minute(), gps.time.second(),
gps.location.lat(), gps.location.lng(), gps.altitude.feet(), gps.satellites.value());

// C. Write to SD
if (sdEnabled) {
File dataFile = SD.open("/flight.csv", FILE_APPEND);
if (dataFile) {
dataFile.println(dataBuf);
dataFile.close();
} else {
sdEnabled = false; // Trigger recovery on next loop
}
}

// D. Transmit LoRa
if (!txBusy) {
txBusy = true;
lora.startTransmit(dataBuf);
}

lastActionTime = millis();
}

updateDisplay();
}

void updateDisplay() {
display.clearDisplay();
display.setCursor(0, 0);

// Date and Time (Always attempt to show)
if (gps.date.isValid() && gps.time.isValid()) {
display.printf("%02d/%02d/%02d %02d:%02d:%02d\n",
gps.date.month(), gps.date.day(), gps.date.year() % 100,
gps.time.hour(), gps.time.minute(), gps.time.second());
} else {
display.printf("SATS: %d Wait Time...\n", gps.satellites.value());
}

display.println("--------------------");

// GPS Position Data
if (gps.location.isValid()) {
display.printf("ALT: %.0f ft\n", gps.altitude.feet());
display.printf("LAT: %.5f\n", gps.location.lat());
display.printf("LON: %.5f\n", gps.location.lng());
} else {
display.println("GPS: SEARCHING...");
display.printf("Visible Satellites: %d\n", gps.satellites.value());
if (gps.satellites.value() > 2) display.println("Wait for lock...");
}

// SD Status Bar
display.setCursor(0, 56);
if (!sdEnabled) {
display.setTextColor(BLACK, WHITE);
display.print(" SD: ERROR (RETRYING) ");
display.setTextColor(WHITE, BLACK);
} else {
display.print("SD: LOGGING OK");
}

display.display();
}
90 changes: 48 additions & 42 deletions telemetry/esp32-heltec-tracker/c/lesson-7/Lesson_7_Receiver_Code.ino
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Original file line number Diff line number Diff line change
Expand Up @@ -5,73 +5,79 @@
#define LORA_DIO1 14
#define LORA_NRST 12
#define LORA_BUSY 13
#define VEXT_CTRL 3

HT_st7735 screen;

// initalize lora radio and make an interrupt function for when packets arrive
SX1262 lora = new Module(LORA_NSS, LORA_DIO1, LORA_NRST, LORA_BUSY);

volatile bool packetAvailable = false;
ICACHE_RAM_ATTR // puts onReceive in RAM for better memory access

void onReceive(void) {
packetAvailable = true;
}

void setup() {
Serial.begin(115000);
Serial.begin(115200);

pinMode(VEXT_CTRL, OUTPUT);
digitalWrite(VEXT_CTRL, LOW);
delay(100);

screen.st7735_init();
screen.st7735_fill_screen(ST7735_BLACK);
loraInit();
screen.st7735_write_str(0, 0, "RECEIVER READY", Font_7x10, ST7735_YELLOW, ST7735_BLACK);

// Frequency: 915.0 MHz, TCXO: 1.6V, Regulator: DC-DC
int status = lora.begin(915.0, 125.0, 7, 5, 0x12, 10, 8, 1.6, false);

if (status == RADIOLIB_ERR_NONE) {
screen.st7735_write_str(0, 15, "LORA: OK", Font_7x10, ST7735_GREEN, ST7735_BLACK);
lora.setPacketReceivedAction(onReceive);
lora.startReceive();
}
}

void loop() {
if(packetAvailable){
readPacket();
}
}

int loraInit(){
screen.st7735_write_str(0, 0, "LORA init...", Font_7x10, ST7735_WHITE, ST7735_BLACK);
int status1 = lora.begin();
lora.setPacketReceivedAction(onReceive); // tells lora to call the interrupt function when a packet arrives
int status2 = lora.startReceive();

if (status1 == RADIOLIB_ERR_NONE && status2 == RADIOLIB_ERR_NONE) {
screen.st7735_write_str(90, 0, "OK", Font_7x10, ST7735_GREEN, ST7735_BLACK);
} else {
screen.st7735_write_str(90, 0, "ERR", Font_7x10, ST7735_RED, ST7735_BLACK);
screen.st7735_write_str(120, 0, (String)status1, Font_7x10, ST7735_WHITE, ST7735_BLACK);
screen.st7735_write_str(140, 0, (String)status2, Font_7x10, ST7735_WHITE, ST7735_BLACK);
}
return status1 + status2; // can be used for status checking: will be 0 if no errors
}

void readPacket() {
String data;
int status = lora.readData(data); // data is stored into "data" and status is stored is "status"
int status = lora.readData(data);

if (status == RADIOLIB_ERR_NONE) {
screen.st7735_write_str(0, 12, "Data: ", Font_7x10, ST7735_WHITE, ST7735_BLACK);
screen.st7735_write_str(64, 12, data, Font_7x10, ST7735_WHITE, ST7735_BLACK);
screen.st7735_fill_screen(ST7735_BLACK);

// --- ROW 1: HEADER ---
screen.st7735_write_str(0, 0, "PAYLOAD:", Font_7x10, ST7735_YELLOW, ST7735_BLACK);

// --- ROW 2: DATA (Starts at 12, allows wrapping to ~34) ---
screen.st7735_write_str(0, 12, data, Font_7x10, ST7735_WHITE, ST7735_BLACK);

String rssi = (String)lora.getRSSI();
screen.st7735_write_str(0, 24, "RSSI: dBm", Font_7x10, ST7735_WHITE, ST7735_BLACK);
screen.st7735_write_str(64, 24, rssi, Font_7x10, ST7735_WHITE, ST7735_BLACK);
// --- ROW 3: RADIO STATS ---
// Lowered to Y=40 to clear potential 2nd line of payload text
char radioStr[40];
sprintf(radioStr, "RSSI:%-4.0f SNR:%-3.1f", lora.getRSSI(), lora.getSNR());
screen.st7735_write_str(0, 40, radioStr, Font_7x10, ST7735_CYAN, ST7735_BLACK);

String snr = (String)lora.getSNR();
screen.st7735_write_str(0, 36, "SNR: dB", Font_7x10, ST7735_WHITE, ST7735_BLACK);
screen.st7735_write_str(64, 36, snr, Font_7x10, ST7735_WHITE, ST7735_BLACK);
// --- ROW 4: FREQUENCY ERROR ---
char feStr[40];
sprintf(feStr, "FE: %-5.0f Hz", lora.getFrequencyError());
screen.st7735_write_str(0, 53, feStr, Font_7x10, ST7735_WHITE, ST7735_BLACK);

String freqErr = (String)lora.getFrequencyError();
screen.st7735_write_str(0, 48, "Freq Err: Hz", Font_7x10, ST7735_WHITE, ST7735_BLACK);
screen.st7735_write_str(64, 48, freqErr, Font_7x10, ST7735_WHITE, ST7735_BLACK);

} else if (status == RADIOLIB_ERR_CRC_MISMATCH) {
screen.st7735_write_str(0, 12, "CRC Error", Font_7x10, ST7735_RED, ST7735_BLACK);
screen.st7735_write_str(0, 24, "Malformed Packet", Font_7x10, ST7735_WHITE, ST7735_BLACK);
} else {
String err = (String)status;
screen.st7735_write_str(0, 12, "Rx Error:", Font_7x10, ST7735_RED, ST7735_BLACK);
screen.st7735_write_str(80, 12, err, Font_7x10, ST7735_WHITE, ST7735_BLACK);
// ERROR HANDLING (Screen turns red text on failure)
screen.st7735_fill_screen(ST7735_BLACK);
screen.st7735_write_str(0, 0, "RX ERROR!", Font_7x10, ST7735_RED, ST7735_BLACK);
if(status == RADIOLIB_ERR_CRC_MISMATCH) {
screen.st7735_write_str(0, 15, "CRC CORRUPTION", Font_7x10, ST7735_RED, ST7735_BLACK);
} else {
screen.st7735_write_str(0, 15, "CODE: " + String(status), Font_7x10, ST7735_WHITE, ST7735_BLACK);
}
}
packetAvailable = false; // reset flag
}

packetAvailable = false;
lora.startReceive();
}
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