Altitude & Orientation Logger

Overview

The ET-S04 BNO085 does its own sensor fusion and outputs ready-made orientation, so the ESP32 doesn't have to run a filter. The ET-S15 BMP390 barometer resolves height changes of a few centimetres.

The logger records roll, pitch, heading and relative altitude to a CSV file in the ESP32's flash at 50 Hz. It runs from a small LiPo through a 5 V boost, and you download the file over USB after the flight.

• Roll, pitch and heading from on-chip fusion
• Relative altitude to ±0.25 m
• 50 Hz CSV logging to flash
• Light: one LiPo cell, USB-C charging

What you need

ElectroTrical boards

ET-S04BNO085 9-DoF Orientation IMUBNO085 9-DoF orientation with on-chip fusion

AED 79.00Out of stock

ET-S15BMP390 Precision BarometerBMP390 precision barometer for altitude

AED 39.00Out of stock

ET-P05TPS61023 5 V Boost5 V boost from the LiPo

AED 15.00Out of stock

ET-P01MCP73831 USB-C LiPo ChargerUSB-C LiPo charger

AED 22.00Out of stock

Boards total: AED 155.00

These boards are being manufactured. Open a board's page to see when it's back, or ask us about a kit.

You'll also need

• ESP32-S3 DevKitC-1 (or any ESP32-S3 board) with a USB-C data cable. Not sold by ElectroTrical.
• Qwiic / STEMMA QT cables (JST SH 4-pin) to chain the boards, or jumper wires
• Small 1S LiPo, 300–1,000 mAh
• Foam or 3D-printed mount with a small vent hole for the barometer

Wiring

Wire the first board's header to the ESP32 as shown, then link the other I²C boards with Qwiic cables. Every board carries VIN, GND, SDA and SCL through both Qwiic sockets, so the chain needs no extra wires. Addresses: BNO085 0x4A, BMP390 0x77.

Build it

1. 01

   Set up the Arduino IDE

   Install Arduino IDE 2, add the Espressif ESP32 board package (Boards Manager → “esp32” by Espressif), select “ESP32S3 Dev Module” and turn on USB CDC On Boot so Serial prints over USB. Install the libraries listed above the sketch from Library Manager.

2. 02

   Choose the flash layout

   In Tools → Partition Scheme, select one with a large SPIFFS/LittleFS area (for example “Huge APP (3MB No OTA/1MB SPIFFS)” or a 16 MB option if your board has 16 MB flash).

3. 03

   Calibrate the compass

   After power-up, wave the logger slowly in a figure-eight for 20 seconds, away from motors and metal. The BNO085 stores its calibration as it learns.

4. 04

   Mount it

   Fix the boards with the arrows on the ET-S04 pointing forward. Isolate the board from motor vibration with foam, and shield the barometer from prop wash with open-cell foam over the vent.

5. 05

   Log a flight

   Power up on the ground — altitude zero is taken at boot. After landing, plug in USB and type d in Serial Monitor to dump the CSV, or x to erase it.

Arduino code

Written for the ESP32-S3 DevKitC-1 with the Espressif Arduino core. Install these libraries from the Arduino Library Manager:

• Adafruit BNO08x
• Adafruit BMP3XX Library

#include <Wire.h>
#include <LittleFS.h>
#include <Adafruit_BNO08x.h>
#include <Adafruit_BMP3XX.h>

Adafruit_BNO08x bno(16);           // RST on GPIO16
Adafruit_BMP3XX bmp;
sh2_SensorValue_t ev;
float roll, pitch, yaw, groundHpa;

void toEuler(float r, float i, float j, float k) {
  roll  = atan2(2 * (r * i + j * k), 1 - 2 * (i * i + j * j)) * RAD_TO_DEG;
  pitch = asin(constrain(2 * (r * j - k * i), -1.0f, 1.0f)) * RAD_TO_DEG;
  yaw   = atan2(2 * (r * k + i * j), 1 - 2 * (j * j + k * k)) * RAD_TO_DEG;
}

void setup() {
  Serial.begin(115200);
  Wire.begin(8, 9);
  Wire.setClock(400000);
  LittleFS.begin(true);

  if (!bno.begin_I2C(0x4A)) Serial.println("BNO085 not found");
  bno.enableReport(SH2_ROTATION_VECTOR, 20000);          // 50 Hz

  if (!bmp.begin_I2C(0x77)) Serial.println("BMP390 not found");
  bmp.setPressureOversampling(BMP3_OVERSAMPLING_8X);
  bmp.setTemperatureOversampling(BMP3_OVERSAMPLING_2X);
  bmp.setIIRFilterCoeff(BMP3_IIR_FILTER_COEFF_3);
  bmp.setOutputDataRate(BMP3_ODR_50_HZ);

  delay(500);
  float sum = 0;
  for (int n = 0; n < 20; n++) { bmp.performReading(); sum += bmp.pressure / 100.0; delay(20); }
  groundHpa = sum / 20;                                   // altitude zero = here

  File f = LittleFS.open("/flight.csv", FILE_APPEND);
  f.println("ms,roll,pitch,yaw,alt_m");
  f.close();
  Serial.println("Logging. d = dump, x = erase");
}

void loop() {
  if (bno.wasReset()) bno.enableReport(SH2_ROTATION_VECTOR, 20000);

  if (bno.getSensorEvent(&ev) && ev.sensorId == SH2_ROTATION_VECTOR) {
    auto q = ev.un.rotationVector;
    toEuler(q.real, q.i, q.j, q.k);
    bmp.performReading();
    float alt = bmp.readAltitude(groundHpa);

    File f = LittleFS.open("/flight.csv", FILE_APPEND);
    f.printf("%lu,%.1f,%.1f,%.1f,%.2f\n", millis(), roll, pitch, yaw, alt);
    f.close();
  }

  if (Serial.available()) {
    char c = Serial.read();
    if (c == 'd') { File f = LittleFS.open("/flight.csv"); while (f.available()) Serial.write(f.read()); f.close(); }
    if (c == 'x') { LittleFS.remove("/flight.csv"); Serial.println("Erased"); }
  }
}

Troubleshooting

Take it further

• Add the ET-S41 GNSS receiver for position and ground speed
• Trigger a parachute servo at apogee for model rockets
• Use the ET-S27 ICM-42688-P for high-rate vibration logging