High-Altitude Balloon Payload Logger

Weather-style balloons can lift a small payload above 30 km, where the sky turns black. It is a classic school and club project — but it is aviation, so planning, legal limits and recovery matter as much as the electronics.

Mission steps

1. Check the rules

   In the U.S., FAA Part 101 covers unmanned free balloons. Small payloads are exempt from most requirements only if they stay under its weight and density limits (for example, no single package over 4 lb with high density, none over 6 lb and no more than 12 lb in total) and the suspension line breaks under 50 lb of force. Read the current rule before you build.

2. Set the GPS for altitude

   Many GPS modules stop reporting above about 18 km unless you set the dynamic model to an airborne mode using u-blox's u-center software.

3. Log the sensors

   The Pi records GPS position, BME280 pressure and temperature, and a photo every minute to the SD card.

4. Track it

   A LoRa radio sends position packets to a receiver on the ground; ISM-band LoRa modules do not need a ham license.

5. Insulate and test

   Use a foam box and hand warmers, run the full system in a freezer for hours, and predict the landing site with a flight-path predictor before launch day.

Code

import time, csv, subprocess, serial, pynmea2, smbus2, bme280

bus = smbus2.SMBus(1)
cal = bme280.load_calibration_params(bus, 0x76)
gps = serial.Serial('/dev/serial0', 9600, timeout=1)
fix = {'lat': None, 'lon': None, 'alt': None}
last_photo = 0

while True:
    line = gps.readline().decode(errors='ignore')
    if 'GGA' in line:
        try:
            m = pynmea2.parse(line)
            fix = {'lat': m.latitude, 'lon': m.longitude, 'alt': m.altitude}
        except pynmea2.ParseError:
            pass
        env = bme280.sample(bus, 0x76, cal)
        with open('/home/pi/flight.csv', 'a', newline='') as f:
            csv.writer(f).writerow([time.time(), fix['lat'], fix['lon'], fix['alt'],
                                    round(env.pressure, 1), round(env.temperature, 1)])
    if time.time() - last_photo > 60:
        last_photo = time.time()
        subprocess.Popen(['rpicam-still', '-n', '--immediate',
                          '-o', '/home/pi/img_%d.jpg' % last_photo])

Tip: test every script on the bench before installing it in a moving machine.

Questions