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a variometer provides audio feedback on copter rising/falling and vertical speed. In the glider world this is a well known device to aid in following thermals; with copters it should help in obeserving altitude or maintaining altitude without explicit alt.hold.

The audio output gets modulated depending on direction (up or down) and vertical speed. With higher speed, the silent spacing between signals gets shorter and the tone duration gets higher.

Output is done over serial (wireless via BT or xbee etc.) to a vt100 terminal program available for most smartphones/handhelds, computers etc.(I use an old palm treo for testing). The variometer does work with the single tones from regular vt100 terminal program. For the experimental souls, a terminal program specifically for android is available to produce two different tones; .

Current impelementation utilizes two methods to detect rising/falling speed. Method 1 relies on short term variation of the 'vario' variable while method 2 does a long term delta of altitude. Either one of the two or both metods can be activated.


  • working baro
  • vt100 terminal program with audio output for BELL (0x07) command (available for most devices like smartphones/handhelds, computers)
  • working wireless connection between copter and device

How To


  • activate in config.h with VARIOMETER set to one or two methods
  • select one or two tones output (depending on your vt100 program)
  • optionally limit detection to either rising or falling movement
  • enable LCD_vt100
  • if you have not done yet, install vt100 terminal program on your ground device (link to the enhanced vt100 terminal program for android: ... 274&r=1274)


  • assign activation of variometer to an aux switch via GUI or LCD config menu as usual,
  • establish working serial connection over wireless between copter and ground device
  • fly and activate via aux channel switch.