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Difference between revisions of "Howto:Use Arduino with FlightGear"

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Revision as of 03:58, 10 February 2015

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 respond 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:

      FGFS Input Test
      Reads a digital input on pin 7, prints the result to the serial port.
      Reads a potentiometer input on A0 and print result to serial port.
      This example code is in the public domain.
    int potPin = 0;       // potentiometer on A0
    int switchPin = 7;    // switch on pin 7
    float potValue = 0;   // float variable to store potentiometer value
    void setup() {
    Serial.begin(9600);          // open serial connection
    pinMode(switchPin, INPUT);   // pin 7 declared as input
    void loop() {
    Serial.print(digitalRead(switchPin));   // read and print switch state
    Serial.print(",");                      // print ,
    potValue = analogRead(potPin);          // read potentiometer and store it to potValue
    potValue = potValue / 1024;             // divide potValue with 1024 to make it between 0 and 1
    PrintDouble(potValue, 2);               // pass potValue to PrintDouble-function, read from below what magic happens
    Serial.print("\n");                     // print new line
    delay(500);                             // delay only for making this guide easier to follow on serial monitor
    void PrintDouble(double val, byte precision){
      // prints val with number of decimal places determine by precision
      // precision is a number from 0 to 6 indicating the desired decimial places
      // example: lcdPrintDouble( 3.1415, 2); // prints 3.14 (two decimal places)
      // From http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1207226548
      if(val < 0.0){
        val = -val;
      Serial.print (int(val));  //prints the int part
      if( precision > 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:

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.
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 Flightgear, Arduino and Linux

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:

 <?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