The Variod is a Linux program with the following functions:

  • Communication to XCSoar
  • User Interface for Volume Control and Tone Settings
  • Audio-Vario and Speed to Fly

The Variod obtains data from XCSoar and from the sensord. Have a look at the General operation principle to understand the details.

Internal Data Flow

Sensors –> [i2c bus] –> sensord –> [NMEA over TCP port 4353] –> variod –> [NMEA over TCP port 4352] ←→ XCSoar

Command Line Options

Usually the Variod runs in the background as a daemon, but for special purposes it is possible to start variod with options. Here is a short overview about the possibilities:

variod  -v              print version information
variod  -f              don't daemonize, stay in foreground
variod  -c [filename]   use config file [filename]
variod  -d[n]           set debug level. n can be [1..2]. default=1

The sound characteristics of the Audio-Vario is defined in the default config-file:


The following parameters can be set according to your personal preferences:

Audio Vario Configuration

Name Description Unit Example
Deadband Low The lower limit for the deadband of the audio vario. m/s -0.2
Deadband High The upper limit for the deadband of the audio vario. m/s +0.5
Pulse Length The length of the pulse generated by the vario synthesizer samples 12500
Pulse Length Gain The gain the pulse length will be boosted if vario value increases 1.1
Base Frequency Positive Frequency of the vario tone if vario value is positive Hz 402
Base Frequency Negative Frequency of the vario tone if vario value is negative Hz 350

Speed to Fly Configuration

In preparation

Global Volume Control

Global settings of audio-parameters can be made using the alsamixer from the shell, a graphical program which is part of the OV-Linux-Kernel. We recommend to set the master gain to 100%. The settings can be saved with the command alsactl store.

NMEA Syntax

The Variod receives Commands from XCSoar using the following NMEA-strings:

NMEA-String Description Unit Example
POV Initial String for OpenVario
C Command Mode (XCSoar sends Pilot's Commands to Variod)
MC Mac Cready Value from XCSoar m/s 1.2
WL Wing Load Factor 1.0 is with no ballast
BU Bugs (on the aerofoil) % 10
POL Polar Coefficients a,b,c in preparation
VU Volume Up in 10 steps
VD Volume Down in 10 steps
VM Volume Mute Toggle ON/OFF
VAR Set Vario Mode VAR
STF Set Speed To Fly Mode STF

The NMEA-strings above are for the Variod only, the complete information about all NMEA-strings used by Openvario can be found here:


Volume Control during Flight

The corresponding User Interface in XCSoar can be found in Quick Menu → Vario

XCSoar Vario User Interface

The Audio Vario has to be activated in XCSoar.

Warning: The sound configuration from XCSoar can be found at Config → Gauges → AudioVario, but it has no effect at all! At the moment the sound configuration has to be done by editing the file variod.conf manually, as described above.

Source Code Details

If you want to know what's inside the variod, you can use a git client to obtain the source code on your local computer.

git clone

Navigate to sensord

Go back to Overview

Go to Audio Vario / Speed to Fly

Go to Setup Guide