Steve Griffin's Balloon Building
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AutoPilot Project

A balloon's fuel consumption is increased when in climbing and descending flight because of of the increased cooling rate encountered when air flows over the envelope. This additional fuel burn can be significant and leads to decreased duration performance.

The aim of this autopilot project is to have the balloon automatically fly at a pre-assigned altitude. Control will be effected by a micro-controller operated electric blast valve which operated in parallel to the pilot operated blast valve.

Auto Pilot Block Diagram

Pressure Sensor

I selected the Intersema MS5534A barometer module as the pressure sensing device.

The MS5534 features:

  • Integrated pressure and temperature sensors
  • Pressure range 300 - 1100 mbar
  • Temperature range -10oC - +60oC
  • 15 bit ADC
  • 3 wire serial interface
  • Low voltage / low power requirements
  • 6 coefficients for software compensation stored on chip.

Intersema provides a number of datasheets for their pressure sensors which 'should' speed the development of the system.

 

Micro-controller

Microchip produce a range of micro-controller IC's, the PIC16F84A is a 20Mhz, 13 I/O port device with 1024 words of flash program memory on board. Whilst devices of much higher performance are available this particular application doesn't really require the additional grunt of the 16F87* series controllers.

More information on the 16F84A can be found here.

Software Development

Microchip provides an integrated development environment called MPLab for software development. Commercially available compilers in  C / C++, PICBasic, PASCAL are available which link into MPLab. I have chosen meLabs PICBasic as my development language because it was easy to learn and understand.

The program has 4 operating modes - Standby, Setup, Learn & Run. Operating flowcharts for each mode are as follows: