High Altitude Balloon for the Global Space Balloon Challenge.
Electronics without battery is 70 grams, battery is 98 grams.
The primary microcontroller used is a Teensy 3.5. The Teensy is a Arduino-compatible ARM based development board.
Software will be based on the Trackuino project with modifications for Teensy DAC support from this project.
Telemetry will be sent via 2m APRS using the HX1 2m Transmitter. This module has an output power of ~300mW tuned to a frequency of 144.390 MHz. There are reports of frequency drift with temperature, so this behavior will have to be characterized before launch.
Antenna will be a simple half-wavelength dipole, likely based on this or this.
Use standard headers etc. Symbol /O (Primay symbol table, symbol ID 'O' corresponding to balloon). Message type based on "Lat/Long Position Report Format — with Data Extension and Timestamp" in the APRS spec.
String:
[Data Type ID flag:/]HHMMSSh[Latitude ddmm.hh[N/S](8b)][SymtableID (1b)][Longitude dddmm.hh[W/E](9b)][Symbol Code (1b)][Course/Speed (7b)][Arb. data (36b)]
| Chars | Description | Example |
|---|---|---|
| 5 | Timestamp (sec) | 12000 |
| 1 | Separator | , |
| 5 | BMP180 Temperature (C) | -60.0 |
| 1 | Separator | , |
| 6 | BMP180 Pressure (Pa) | 101580 |
| 1 | Separator | , |
| 4 | Thermistor ADC Value, max 1023 | 1017 |
| 23 | Total |
Pinout
| Pin Label | Functionality | Connection |
|---|---|---|
| 1, 3 | RF Ground | SMA Shield |
| 2 | RF out | SMA Center pin |
| 4 | Active-high Enable | Digital pin 11 |
| 5 | 5V Supply | N/A |
| 6 | GND | N/A |
| 7 | TX Data | DAC1 |
Outputs NEMA strings over serial, so should integrate with Trackuino's code nicely. Might have to do some configuration via UART. See page 175 of protocol spec for NMEA config.
Config example code: http://playground.arduino.cc/UBlox/GPS Other tutorial: http://ava.upuaut.net/?p=738
The settings we'll need:
- Set non-GPS source's ID's to GPGGA for compatibility
- Double check all available sources are enabled
- Disable some unnecessary debug outputs
- Figure out how to switch between low and high altitude mode
- Change refresh rate
| Pin Label | Functionality | Connection |
|---|---|---|
| SDA | I2C | N/A |
| SCL | I2C | N/A |
| TXD | Serial UART | Serial4 RX |
| RXD | Serial UART | Serial4 TX |
| GND | Ground | |
| VCC | 3.3V Power |
Use the Sparkfun library. Communicates over I2C, nothing fancy. Must use SCL/SDA0 since those correspond to the default Wire interface.
| Pin Label | Functionality | Connection |
|---|---|---|
| VIN | 5V power in, feeds on-board regulator | N/A |
| 3V3 | 3V3 power rail | N/A |
| GND | Ground | Black |
| SCL | I2C | SCL0 (Pin 19) |
| SDA | I2C | SDA0 (Pin 18) |
Use the Adafruit library. Communicates over I2C.
| Pin Label | Functionality | Wire Color |
|---|---|---|
| VIN | 5V power in, feeds on-board regulator | NC |
| 3Vo | 3V3 power rail | N/A |
| GND | Ground | Black |
| SCL | I2C | SCL0 (Pin 19) |
| SDA | I2C | SDA0 (Pin 18) |
| A | Address Select | NC for address 0x1C |
| I1 | Interrupt 1 | NC |
| I2 | Interrupt 2 | NC |
Hook it up with a 10k resistor in a voltage divider setup, read with ADC. Connected to ADC17