Political Atmosphere

"Political Atmosphere" by Felix Lenz traces the invisible connections between flight turbulence, climate change and war. My task was to write the code for this installation.

3 min read

Siren in a dark room Deafening siren

“Political Atmosphere” by Felix Lenz traces the invisible connections between flight turbulence, climate change and war. Flight data is captured by an antenna and sent to a controller. Felix asked me to visually display the flight data and correlate the measured flight density in the sky with the speed of a DC motor. This motor turned a gearbox which ultimately triggered a siren. The more planes in the sky, the more frequently the centerpiece of the exhibition - the deafening siren - is triggered.

antenna and a plane Antenna captures data

Acrylic gearbox

The Code

The open source software dump1090 was used to translate the antenna data to json data. This data was then fetched by a React App running inside Electron. If there was a change in flight-density, the React App emitted the data via a websocket. On the receiving end was a Node.js script that controlled the speed of the DC-Motor by changing the pwm signal. This was done by using a L298N motor controller.

// React App running inside Electron
import React, { Component } from 'react';
import Axios from "axios";
import io from "socket.io-client";

let current = 0;
let gain = 0;
let density = 0;
let refresh = 0;
let pwm = 0;
const socket = io(localhost:PORT);

class App extends Component {
  constructor(props) {
    super(props);
      this.state = {
        flights: []
    };
  };
  
  // Get flight-data from dump1090
  async componentDidMount() {
    try{
      setInterval(async () => {
        Axios.get("http://localhost:8080/data/data.json").then((response)=>{
          this.setState({
            flights: response.data,
		  });
	    });
      }, 5000);
    } catch(e) {
      console.log(e);
    }
  }
  
  // Do something with the flight-data   
  render () {
    // Some simple flight density logic
    current= this.state.flights.length;
    gain= (current > gain) ? current : gain;
    density= Math.round((100*current)/(gain));
    pwm = density;
    
    // Emit 
    if (pwm !== refresh) {
      refresh = pwm;
	  socket.emit('message', {density: pwm});
    }
	  
    // Visual Interface
    return (
      <div className="App">
        {/* funky React interface goes here */}
      </div>
    );
  }
}

export default App;

// Node.js motor-controller running on a Raspberrypi
// Require modules
const Gpio = require('pigpio').Gpio;
const io = require("socket.io")(PORT);

// Setup GPIO 
const in1 = new Gpio(23, {mode: Gpio.OUTPUT});
const in2 = new Gpio(24, {mode: Gpio.OUTPUT});
const en = new Gpio(25, {mode: Gpio.OUTPUT});

in1.digitalWrite(0);
in2.digitalWrite(0);

// Set motor speed
function setSpeed( message ) {
  let pwm = message.density;
  if (pwm === 0) { 
    in1.digitalWrite(0);
	in2.digitalWrite(0);
  } else {
    in1.digitalWrite(0);
    in2.digitalWrite(1);   
    // Setting the pwm signal
    dutyCycle = pwm < 30 ? 75 : Math.round(255 * pwm/100);
    en.pwmWrite(dutyCycle);
  }
}

// Flight-data from the server
io.on("connection", async socket => {  
  socket.on("message", async messageData => {
    let message = messageData;
    await setSpeed(message);
  });
});

process.on('SIGINT', function() {
  in1.digitalWrite(0);
  in2.digitalWrite(0);
  process.exit();
});

Siren and interface are outside ARS Electronica 2020

All images are © Felix Lenz 2020. The Project “Political Atmosphere” was designed by Felix Lenz. If you want to read more about it, visit his website. Learn how to run a React App inside Electron here.

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