Circuit Lake

Variometer is a device commonly used by pilots of various kinds of air vehicles to visualize the vertical speed. The device is of importance for the ones who want to fly without any engine like paraglider and hanglider. It help glider pilot decide whether to escape from the sink area or to start soaring in the rising area called a thermal. Because after a few up/down bumps no one is able to tell if he is still rising or already sinking without variometer.

This Variometer-Altimeter project is cost-saving alternative to commercial devices. It can measure vertical speed and altitude with reference to sea level or to start point level. The system is built around MCU AVR ATmega16 and Motorola’s MPX4115 electronic pressure sensor. The output from that device, after conditioning, is forwarded to the 24bit, serial ADC. The measurements taken by the ADC are transferred over the SPI bus to the heart of project, the atmega16 microcontroller. The software then calculates the outside air pressure. Having measured the pressure we can derive the current standard atmosphere altitude, called also the pressure altitude. Calculating the difference between subsequent measurements of altitude we finally have the vertical speed.

The calculated value of the vertical speed is then compared with the set thresholds (separate for positive and negative vertical speeds). If current speed exceeds the threshold then the sound generation subroutine is activated. For positive speed the variometer plays interupted sound of frequency proportional to the value of speed. For negative speed the sound is continuous, it has lower frequency but also proportional to the value of speed. AVR based Variometer-Altimeter is designed by Michal Gomulinski from Poland.