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Howto:Use Arduino with FlightGear

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Arduino is an open-source electronics prototyping platform based on flexible, easy-to-use hardware (consisting of a board designed around an 8-bit or a 32-bit microcontroller) and software Arduino IDE). FlightGear's IO interface allows easy development of hardware that can improve the immersion and realism of the simulation. The output protocol allow hardware to response to simulation data, while the input protocol allows FlightGear to reply to hardware events (e.g., on the press of a button).

How to: Control Flightgear with Arduino

With this "how to", you are able to do a switch and a potentiometer interface to control Flightgear's properties such as aileron, elevator, gears, lights, fuel valve, etc..

Equipment and software

This example uses following components and software:

  • FlightGear 3.2
  • Flightgear Launch Control (program to make FlightGear start without terminal command and options)
  • Arduino UNO
  • Linux (Ubuntu 14.04)
  • On/off switch
  • Potentiometer
  • Flightgear's Cessna 172P Skyhawk

Input protocol file

Input protocol file is used to specify how serial information is read by Flightgear. In Ubuntu protocol files are found in: "/usr/share/games/flightgear/protocol" directory.

Protocol file structure

Create controltest.xml file to your protocol folder and paste code from below to it.

 <?xml version="1.0"?>

Explanation of lines:

  • Line separator: "line_separator" is used to tell Flightgear that a line of commands is at end and new one is starting. In this example file its "/n" and it means new line.
  • Variable separator: "variable_separator" is used to tell Flightgear that another variable is after this mark. In this protocol file it's ",".
  • Chunk: "chunk" is to specify area for one variable and it's information.
  • Name: "name" is used only for identifying variable so it can be anything.
  • Node: "node" is an address to tell what property in Flightgear is changed. In this example it is "/controls/lighting/strobe" and "controls/engines/engine/throttle".
  • Type: "type" line tells what kind of command is send. In this example it is a "bool" and that means a boolean type of property of a "float" for float.

For a better explanation of configuration file, read Generic Protocol wiki page. You can find a list of properties that can be controlled from a Flightgears docs-folder a file called "README.properties". Or you can use Flightgears Property Browser from main menu: Debug > Browse Internal Properties. Properties in protocol file needs to be in same order as they are send from Arduino.

Wiring and coding Arduino


Potentiometer is connected to Arduinos ground and +5 volts. Potentiometers middle connector is connected to A0 analoq input. Switch is connected to ground with 10 kOhms pull-down resistor and +5 and digital pin 7.

Wiring schematic for connecting potentiometer and switch to Arduino


Copy this code to Arduino IDE and send it to Arduino Uno:

 0) {
        Serial.print("."); // print the decimal point
        unsigned long frac;
        unsigned long mult = 1;
        byte padding = precision -1;
      mult *=10;
        if(val >= 0)
     frac = (val - int(val)) * mult;
     frac = (int(val)- val ) * mult;
        unsigned long frac1 = frac;
        while( frac1 /= 10 )
        while(  padding--)
        Serial.print(frac,DEC) ;

====Test serial output====

Use Arduino IDEs serial monitor and you should see something like this:
[[File:Flightgear arduino serial monitor.png|frame|none|Arduino IDEs serial monitor output]]

First number is switch data, so it's either 0 (switch off) or 1 (switch on). After "," mark is our throttle data. First it's 0.00 meaning idle throttle and then potentiometer is gradually turned until it reaches 0.99.

{{Warning|Remember to '''unplug Arduino's USB cable and plug it back''' in because Flightgear won't be able to read serial without doing this! You have to do this every time after you use Arduino IDE.}}

====Start Flightgear====

Flightgear needs to be started with a correct command line option for it to be able to read serial connection. This example uses following option:


If you like, you can use graphical user interface, Flightgear Launch Control (aka FGRun), to launch Flightgear. Select correct settings from Advanced Option tab. [[File:Starting Flightgear with input options enabled.jpg|thumb|none|Starting Flightgear with FGLaunch Control, selecting input/output options]]

If you don't now your correct port, you can check it with a following command in terminal: dmesg | tail. It should give you a message something like: "ttyACM0: USB ACM device" or "ttyACM1: USB ACM device". That's your port. Finally save setting by clicking 'OK' and click 'Run' to start flightgear. For more detailed guide, see [https://sites.google.com/site/flightgeararduinoandlinux/home Flightgear, Arduino and Linux]

[[File:Arduinofgfs.jpg|thumb|270px|Arduino LCD panel displaying speed, heading and altitude.]]
== Display/Generic protocol Example by rubdos ==

Rubdos (Ruben De Smet) has built an example using the [[Generic Protocol]] and an Arduino Mega 2560.
The code used to control the Arduino with generic protocol was:
<syntaxhighlight lang="xml">
 <?xml version="1.0"?>
 <!--        <input>

It is a simple plaintext protocol, which can easily be parsed by an Arduino. The code used on the Arduino is available on github as a gist: [1]

As hardware, five seven segment displays were used, multiplexed straight on the Arduino device. In production, you'd rather use some 74HC595 or other shift register chips to drive them, to unload the Arduino and have more current. A demo is uploaded to youtube, with voiceover in which the display shows the RPM of the first engine of (the single engine) DR400: [2]

Related content

External links