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balloon_trackers

Trackers Project

Feel free to update this page with useful information you find

Our Trackers

    • 434.451MHz LORA / RTTY
    • RTTY: 50bd 7n2
    • LORA: SF10, 41.7KHz, 4/8 FEC

Tracker Architecture

A balloon tracker commonly consists of 4 main parts: Power Source, CPU, GPS Receiver, Radio Transmitter.

Power Source

In the low temperatures experienced at altitude, consumer alkaline batteries suffer a massive degradation in capacity, leading to extra weight being required and unpredictability of battery life.

e.g. Energizer Alkaline AA Battery Datasheet

We therefore use Li/Fe Chemistry cells that have a far better low temperature response, while maintaining the high current capability required for GPS Receiver and Radio Transmitters. These are most easily available as Energizer Ultimate Lithiums, and can be found in AA/AAA form in most large supermarkets.

Energizer Ultimate Lithium AA Datasheet

CPU

This is normally a Microcontroller such as an AVR (used in most Arduinos), PIC, or ARM.

For standard GPS and Sensor Telemetry, a microcontroller is preferred as these are powerful enough, and very energy efficient. For more computationally intensive tasks, such as Live Images, more powerful solutions such as a Raspberry Pi have been used.

GPS Receiver

This can be any off-the-shelf GPS Module, however care has to be taken to check that its implementation of the COCOM Limits allows operation above 18km altitude. Some have been observed not to recover without a reboot after having been above 18km, so a limited module should never be flown.

In addition the choice of GPS antenna can be important. The more common 'Patch' antennas do not work well when inverted, which can cause issues if the payload lands upside down, or is disturbed in flight. More omnidirectional designs such as helixes and chip antennas can be more suitable for HAB.

Anthony at HAB Supplies sells a range of ublox breakout boards, of varying suitability. - HAB Supplies GPS Breakout Boards

Radio Transmitter

As the use of Amateur (Ham) Radio is not permitted Airborne in the UK, Radio Transmission is done on Airborne-permitting ISM Bands, such as 434MHz and 869MHz.

434MHz is the more commonly used by the Ballooning Community due to lack of restrictions on duty cycle, and coverage by easily available Amateur Radio Receivers. The power limit in this band is 10mW.

Groups

Team A : Joe, Barbara, Alex

Team B : Laura, Janki, Mahesh, Suzi

Background Reading

Potential Core Processors

  • Arduino - Generally the best for beginners, based on the AVR processors, but has a nice series of libraries to make it a bit easier to use
  • AVR - Can be used without the arduino libraries, but means you need to read the datasheet to work out how to use the hardware
  • MSP430 - An alternative to the AVR
  • PIC - Another alternative
  • Raspberry pi - Uses more than the above options, generally the extra processing power it can provide isnt needed for regular tracker. It can be used to send back still images, but with careful programming this can be done with the above options

Radio Modules

The radio needs to be able transmit on 434MHz at 10mW (this is pretty low power). The standard protocol shifts the frequency of the radio to represent a 1 or 0 (frequency shift keying - FSK). The main choices are as follows:

  • NTX2b - a simple module that operates on a fixed frequency range (different options available). Changing the voltage on an input pin alters slightly the transmitters frequency
  • RFM22b - a more complex module that requires some digital communication between the module and the processor to change the frequency. The frequency range of operation can be changed so it does not clash with any other trackers' transmitters that might be also transmitting
  • cc1101 modules - a selection of modules based around the cc1101 IC can be found, which is similar in operation to the RFM22b

Some guides on how to connect a transmitter and receive the data: Connecting a NTX2 to an arduino

GPS Modules

The is only really one module I would suggest using - the ublox MAX7 (or MAX6). Can talk to the microprocessor using UART (like rs232 serial) or I2C (another serial communication standard). The main point to remember about this modules is that they have a 'flight mode' that needs to be activated to stop it getting confused above 12km.

GPS modules in general give out NMEA strings every second, but exactly what they send and how often can be configured. The NMEA GPGGA string gives the position data, and it is up to the processor to parse this string and exract the useful information. (The is a arduino library to do this, but I would suggest you write this bit of code yourself)

Sensors

After you have got the GPS and radio working, the next bit can be to add sensors. Examples are temperature, humidity, pressure, battery voltage, radiation, UV and so on.

balloon_trackers.txt · Last modified: 2016/06/01 02:23 (external edit)