Oscilloscope addon

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This screenshot shows the usual c172p "magnetos checking" Channel 1 (yellow) is rpm (100 rpm / div).Channel 2 (mauve) is magnetos (1 / div).Time sweep is 200 ms / div.[1]

The oscilloscope addon was created as an example of the use of 3 helpers included in the addon:

  • skinnable.nas to create Canvas GUI dialogs including multiple clickable layers.
  • graph.nas to create various types of Canvas instruments.[2]
  • plot2D.nas the very basic Canvas helpers.

But apart from that, the oscilloscope addon itself may be an useful tool for developers and coders. Although I do not know any aircraft that has this instrument in its panel, the on-board engineer will eventually appreciate having it on hand at some point.


Cquote1.png I was just thinking today that it might be cool to have a built in grapher for simple / quick graphing needs.

With the property system it would be trivial to pick an arbitrary property from the property tree and graph it over time -- superimposed on top of everything else. Things get a bit trickier if you want to control scaling, how much time history get's graphed, multiple values, etc., but even graphing a single value (or maybe just two values) over time could be of some use.

I thought I'd toss this out there in case someone thought it was worth while enough to tackle.[3]
— Curtis Olson

How to install

Note  This is the latest version (Jan 30, 2018)
Note  From version 2017.4.0, the FlightGear launcher accepts the --addon option in the Settings/Additional Settings tab.

If your FlightGear version accepts Addons, you can download this feature from the FGAddon repository. Download all the 11 files into the directory of your choice.

Launch FlightGear including --addon argument, for example:

fgfs <usual args> --addon=/path/to/fgaddon/Oscilloscope

Otherwise, you can install it as a submodule. Contact the author for further instructions.

How to use

Manual mode

Just pressing the o key the oscilloscope window appears:

Oscilloscope (default skin).png

Clicking the ? button you will have a basic help about clickable areas and readings. Click ? again to close the help.

Connecting to a source

Click any BNC connector (Channel 1 or Channel 2) to open the Channel Source dialog.

Source dialog.png

Enter a valid source as:

  • A numeric or boolean property, for example:
  • A numeric Nasal expression, for example:
getprop("/engines/engine/rpm") /100 ; (do not forget the ;)
0 ; (only useful to adjust Offset)
5+4*math.sin(D2R*int(100*systime())) ;

Since the time of oscilloscope is the same as simulated one, simulation must not be paused in order to see the resulting plots.

The window above the connector will display the current source value.

Adjusting gain and offset

Clicking the upper/lower half of the Gain knobs will increase/decrease the gain of the channel.

The window below the knob will display the current gain (units/div).

The Offset knobs respond in a similar way.

Adjusting timebase

Proceed in the same way with the Timebase knob. The window below the knob will display the current sweep speed (secs/div).

One Shot store

Clicking this button will erase the screen and prepare Channel 2 to act as trigger.

Channel 2 must be an integer or boolean property. Once its value changes, a single sweep is triggered and the screen freezes.

Click this button again in order to return to the default continuous sweeps.

Scripted mode

Note  Buttons and knobs will still reacting to manual clicks.

Instead of launching the oscilloscope with the o key and clicking buttons and knobs, it is possible to instantiate the instrument from a Nasal script.

Open the Nasal Console (or the REPL interpreter if you prefer) and execute these lines:

var Osc = oscilloscope.show.new();
var myFunc = func {return 10+4*math.sin(D2R*int(100*systime()));};
Osc.setChannelInput(1, myFunc);
Osc.setGain(channel:1, gain:2);
Osc.setGain(channel:2, gain:2);

You can explore other nasal instructions like:

Osc.setChannelInput(2, func {return 5.5;});
Osc.setChannelInput(1, 'var alt = getprop("/position/altitude-ft"); return alt/10;');


  1. rleibner  (Jan 6th, 2018).  Re: Plot2D and graph helpers .
  2. rleibner  (Dec 27th, 2017).  Re: Spoken GCA .
  3. Curtis Olson (Fri, 08 Mar 2002 07:43:35 -0800). idea ... (?).

Related content

Wiki article

  • FGPlot - A preceding effort to create a plotting dialog.

Forum topic

Source code