Open Source Flight Intrument Documentation [index]

Character Based Instrument Manual

Buttons
Editing
Screens
Main Screen
User Settings Screen
Diagnostics Screen
User Settings
ASI Zero
ASI Scale
Alt Adjust
Vario Cal
TEC Effect
Spkr Volume

Buttons

On the front of the instrument are five buttons as shown in the diagram below.  These are all joystick type buttons which can be activated by either pressing in the centre of the button or moving the joystick up, down, left or right.

Buttons

The first (leftmost) joystick is used for navigating between the various screens in the screen loop.
The second joystick is used for navigating between the various navigable fields within a screen and to modify fields while in edit mode.
The third joystick (ENTER) is used to edit the value of navigable fields.
The last two joysticks are used to turn the instrument off and on.

Editing

Various fields on certain screens can be edited.  These fields can be navigated to using the direction arrows (on the second joystick).  The field that has focus will be framed with square brace characters '[' and ']'.  Once a field has focus it may be edited.  To enter edit mode, press ENTER (centre of the third joystick).  The rightmost character of the field will be blinking while in edit mode.  The up and down arrows will cause the field to increment and decrement respectively by one.  The right and left arrows will cause the field to increment and decrement respectively by a larger amount.  To leave edit mode and save the new value of the field, press ENTER again.  To leave edit mode and revert to the old value of the field, press either NEXT or PREV.

Screens

The various screens are arranged in a loop.  Pressing NEXT (moving the first joystick up or right) causes the next screen in the loop to be displayed.  Pressing PREV (moving the first joystick down or left) causes the previous screen in the loop to be displayed.

Main Screen

This is the default screen that appears after powering up the instrument.

                                           
Vario Average >        
+ 2
 . 6
                       < Vario Bar Graph
Time > 1 2 : 3 4 : 5 6                   ^ ^   < Increase Speed to Fly
                   
1 0 2 4
      5 7 < Airspeed
Wind Direction and Speed > 2 7 0 ° 1 8                             < Decrease Speed to Fly
          Altitude ^                  

The fields are as follows.

Vario Bar Graph The graph occupies the first row of the display and is centered about the centre of the row. It represents the instantaneous rate of climb. Each character represents 0.5m/s. The graph fills from the centre towards the right margin as the rate of climb increases. If the lift increases further, the graph starts to clear again from the centre.

Negative rates of climb are the same but in reverse ie. the graph fills from the centre towards the left margin.
Vario Average This shows the rate of climb averaged over time. When the vario bar graph is occupying the right half of the first row, the vario average is shown in the left half, and vice versa. The units of the field are metres per second.
Airspeed The instantaneous airspeed. The units of the field are kilometres per hour.
Increase Speed to Fly The number of up arrows appearing in this field indicates how much the glider's airspeed should be increased by in order to acheive the optimum speed to fly in the current conditions.
Decrease Speed to Fly The number of down arrows appearing in this field indicates how much the glider's airspeed should be decreased by in order to acheive the optimum speed to fly in the current conditions.
Altitude The units of the field are metres above mean sea level.  This field can edited.
Time When a GPS is not connected, this field represents the time elapsed since turning on the instrument.

When a GPS is connected, this field represents the time of day.
Wind Direction and Speed (Not yet implemented).  When a GPS is connected, this field represents the wind direction in degrees and wind speed.

User Settings Screen

This screen allows all of the user settings to be viewed and edited.  The first row always has focus.  The list can be scrolled through using the direction arrows.

                                           
  T E
 C
   E f f e c t [   1 0 0 ] %        
  A S I   Z
 e
 r o     =   5 8 0
            
  A
 S
 I   S
 c a l e   =
1
 0
 0 %          
  S p k r   V o l     =   2 0 0 / 2 5 5    
                             

 

Diagnostics Screen

This screen displays the battery voltage and the internal temperature of the instrument.

                                           
 


 






 




       
  T
 e
 m
 p =
1
 2
 . 7 °
 C


           
  B
 a
 t t
 =

6
 .
 1 2 V



         
 



 


   
 




 
  
    
                             

 

User Settings

The following are the settings which can be modified by the user to either calibrate or customise their instrument.

ASI Zero

This setting is used in conjunction with ASI Scale user setting to calibrate the pitot-static airspeed indicator.  ASI Zero should be set first as a coarse calibration, then ASI Scale is used to fine tune the calibration.  If ASI Zero is modified, ASI Scale will need to be recalculated.

The procedure for calculating the ASI Zero setting is as follows.
Pitot-static airspeed systems are notoriously inaccurate at low airspeeds (<30kmh).  This means that even after ASI Zero has been set there will be times when at zero airspeed the instrument reads anything from zero to 25kmh.  This is not necessarily a sign that the instrument needs recalibrating.

ASI Scale

After setting ASI Zero, the airspeed values displayed by the instrument can be further calibrated with the ASI Scale setting.  This setting is a percentage factor that will be applied to the airspeed.  Thus if ASI Scale is set at 100% but the instrument is reading 50kmh while the airspeed is really 60kmh, ASI Scale should be increased to 120%.

Alt Adjust

This setting is used to modify the displayed altitude to account for changes in barometric pressure due to the prevailing weather conditions.  The value is in metres plus 300 above or below standard conditions.  ie. When QNH is 1013hPa, Alt Adjust should be 300.  When QNH is greater than 1013hPa (in a high pressure weather system), Alt Adjust should be greater than 300.  Similarly when QNH is less than 1013hPa (in a low pressure weather system), Alt Adjust should be less than 300.
A simple way to set Alt Adjust is by editing the altitude field in the main screen while at a known altitude eg. on launch, so that the current altitude is correct.  This automatically sets Alt Adjust to the correct value.

Vario Cal

The instantaneous vertical speed readings of the instrument can be calibrated with the Vario Cal user setting.  Vario Cal is a percentage value which is applied to the instantaneous vertical speed readings.  If Vario Cal is 100% and a climb of 2.5m/s only registers as 2.2m/s, Vario Cal should be increased to 114%.

TEC Effect

The instrument has Total Energy Compensation functionality.  This means that climbing or sinking which is due to changes in airspeed are subtracted from the calculation of the instantaneous vertical speed.  The amount by which this compensation occurs is controlled by the TEC Effect user setting.  This is a percentage value meaning that when TEC Effect is 100%, full compensation occurs.  A setting of 100% can lead to slightly erratic feedback to the pilot due to horizontal gusts and the fact that the glider may not recover all energy during a pull up.  Settings of around 65% work well for hang gliders.

Spkr Volume

This is a value of between 0 for minimum speaker volume and 255 for maximum speaker volume.