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Howto:Use Arduino with FlightGear

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Revision as of 05:54, 10 February 2015 by Johan G (Talk | contribs) (Testing serial output: Warning → Tip – Since there are no software crashes, broken hardware or injuries)

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Thanks to FlightGear's generic protocol, hardware can easily interface with FlightGear. This hardware can be used to improve the immersion and/or realism of the simulation. Arduino is no exception.

About Arduino

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).

Controlling Flightgear with Arduino

This example demonstrates the use of a switch and a potentiometer to control the Property Tree

Equipment and software

This example uses the following components and software:

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 in your protocol folder and paste code from below to it.

<?xml version="1.0"?>

<PropertyList>

<generic>
    <input>   
        <line_separator>\n</line_separator>
        <var_separator>,</var_separator>
   
        <chunk>
            <name>Strobe</name>
            <node>/controls/lighting/strobe</node>
            <type>bool</type>
        </chunk>
   
        <chunk>
            <name>Throttle</name>
            <node>/controls/engines/engine/throttle</node>
            <type>float</type>
        </chunk>
 
    </input>
</generic>

</PropertyList>

See Generic protocol for a description of the various XML tags.

Wiring and coding

Wiring

A potentiometer is connected to Arduinos ground and +5 volts. The potentiometer's 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 the potentiometer and switch to Arduino

Code

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){
        Serial.print('-');
        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;
        while(precision--)
      mult *=10;
 
        if(val >= 0)
     frac = (val - int(val)) * mult;
        else
     frac = (int(val)- val ) * mult;
        unsigned long frac1 = frac;
        while( frac1 /= 10 )
     padding--;
        while(  padding--)
     Serial.print("0");
        Serial.print(frac,DEC) ;
      }
    }

Testing serial output

Use Arduino IDEs serial monitor and you should see something like this:

Arduino IDEs serial monitor output

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

Tip  Remember to unplug Arduino's USB cable and plug it back.

FlightGear will not be able to read serial without doing this!

You have to do this every time after you use the 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:

--generic=serial,in,30,/dev/ttyACM0,controltest
If you like, you can use graphical user interface, FlightGear Launch Control (aka FGRun), to launch Flightgear. Select the correct settings from Advanced Option tab.
Starting Flightgear with FGRun, selecting input/output options

If you don't know 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 a more detailed guide, see Flightgear, Arduino and Linux

Arduino LCD panel displaying speed, heading and altitude.

Example

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"?>

<PropertyList>

<generic>
    <output>
        <binary_mode>false</binary_mode>
        <line_separator>newline</line_separator>
        <var_separator>newline</var_separator>
        <preamble></preamble>
        <postamble></postamble>

        <chunk>
            <name>Altitude</name>
            <node>/position/altitude-ft</node>
            <type>integer</type>
            <format>altitude=%i</format>
        </chunk>

        <chunk>
            <name>RPM</name>
            <node>/engines/engine/rpm</node>
            <type>integer</type>
            <format>rpm=%i</format>
        </chunk>

    </output>

    <!-- <input>
        <line_separator>newline</line_separator>
        <var_separator>tab</var_separator>
        <chunk>
        </chunk>
    </input> -->

</generic>

</PropertyList>

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