High Altitude Balloon

High Altitude Balloon for the Global Space Balloon Challenge.

Electronics without battery is 70 grams, battery is 98 grams.

Controller

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.

Communications

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.

APRS Message Format

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)]

Comment format

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

HX-1 Transmitter

• Main Page

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

Sensors

U-Blox MAX-M8 GPS Receiver

Datasheets

• Breakout Board
• Hardware Specs
• Protocol Spec

Software

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

I/O

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

BMP180 Barometer/Temperature

Datasheets

• Adafruit
• Library

Software

Use the Sparkfun library. Communicates over I2C, nothing fancy. Must use SCL/SDA0 since those correspond to the default Wire interface.

I/O

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)

MMA8451 3-axis accelerometer

Datasheets

• Adafruit
• Library

Software

Use the Adafruit library. Communicates over I2C.

I/O

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

3950 NTC Thermristor

Datasheets

• Adafruit
• Tutorial
• Lookup Table

Hook it up with a 10k resistor in a voltage divider setup, read with ADC. Connected to ADC17

Actuators

Electric heating pad