I need to implement audio PPM (Pulse Position Modulation) on android
Reference: http://en.wikipedia.org/wiki/Pulse-position_modulation
I want to output PPM from the audio output of the smartphone. The final scope is to create a joystick for radiocontrol. but this library may have many future purposes (follow me, lightbridge, etc.etc.). The radios commonly have a PPM output. Transmitters (and pc flight simulators) commonly have PPM input. My scope is to replace the radio with an android device. I wish to know if there is some piece of code ready to use or should i start from scratch?
EDIT: I found some points where to start
1) smartpropplus is a windows software that receives PPM audio and decodes it http://sourceforge.net/p/smartpropoplus/code/HEAD/tree/SPP4/
2) this is how PPM is structured: http://www.aerodesign.de/peter/2000/PCM/PCM_PPM_eng.html#Anker144123
3) this is a easy image that explains how the signal is structured: http://www.aerodesign.de/peter/2000/PCM/frame_ppm.gif
I calculated that sampling the audio signal at 22000Hz will be sufficient to achieve a good resolution for each channel (22 steps for each channel)
Note: if you are interested in receiving ppm audio signal, you need the android ppm decoder class that you can find here: android PPM decoder audio library
This is how i tested it:
1)recording the generated sound with a PC i can see on "wavepad editor" the waveform and it corresponds to what we need.
2) recording the audio output of the smartphone with a pc and analyzing the audio signal with the software "smartpropoplus" and its debug utilities, i can correctly control the PPM channels with my android app.
3) I connected the phone to a PPM receiver (DJI Lightbridge) but the signal is not correctly received. I suspect that the signal level is not the one expected by the dji device. I will wait your feedback comments, but until that moment, i suspect that i did the best that we can do with android.
NOTE: if you want to use my complete example, you need to use the file joystickView.jar in order to control the channels with a graphical joypad. this is how to use it:
1)download the jar file from this link: https://github.com/downloads/zerokol/JoystickView/joystickview.jar
2) Create a folder called "libs" on the root of your project and place the JAR file into this folder.
Now you can test my app.
file AndroidManifest.xml
<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="com.tr3ma.PPMtestProject"
android:versionCode="1"
android:versionName="1.0" >
<uses-permission android:name="android.permission.MODIFY_AUDIO_SETTINGS"/>
<uses-permission android:name="android.permission.RECORD_AUDIO" />
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />
<uses-sdk
android:minSdkVersion="8"
android:targetSdkVersion="17" />
<application
android:allowBackup="true"
android:icon="@drawable/ic_launcher"
android:label="@string/app_name"
android:theme="@style/AppTheme" >
<activity
android:name="com.tr3ma.PPMtestProject.Test"
android:label="@string/app_name"
android:screenOrientation="landscape"
>
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
</application>
</manifest>
file activity_test.xml
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:baselineAligned="true"
android:orientation="vertical" >
<LinearLayout
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:orientation="horizontal"
>
<TextView
android:id="@+id/stick1VerticalLabel"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_weight="1"
android:ems="10"
android:text="stick1Vertical" />
<TextView
android:id="@+id/stick1HorizontalLabel"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_weight="1"
android:textColor="#ff0000"
android:ems="10"
android:text="stick1Horizontal" />
<TextView
android:id="@+id/stick2VerticalLabel"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_weight="1"
android:ems="10"
android:text="stick2Vertical" />
<TextView
android:id="@+id/stick2HorizontalLabel"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:textColor="#ff0000"
android:layout_weight="1"
android:ems="10"
android:text="stick2Horizontal" />
</LinearLayout>
<LinearLayout
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:orientation="horizontal"
>
<com.zerokol.views.JoystickView
android:id="@+id/joystickViewLeft"
android:layout_width="wrap_content"
android:layout_height="fill_parent" />
<com.zerokol.views.JoystickView
android:id="@+id/joystickViewRight"
android:layout_width="wrap_content"
android:layout_height="fill_parent"
android:layout_gravity="end" />
</LinearLayout>
</LinearLayout>
file Test.java
package com.tr3ma.PPMtestProject;
import android.os.Bundle;
import android.widget.TextView;
import android.app.Activity;
import android.app.AlertDialog;
import android.content.DialogInterface;
import com.tr3ma.PPMtestProject.R;
import com.zerokol.views.JoystickView;
import com.zerokol.views.JoystickView.OnJoystickMoveListener;
public class Test extends Activity {
PPMEncoder ppmencoder;
private TextView stick1VerticalLabel;
private TextView stick1HorizontalLabel;
private TextView stick2VerticalLabel;
private TextView stick2HorizontalLabel;
// Importing as others views
private JoystickView joystickLeft;
private JoystickView joystickRight;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_test);
ppmencoder=new PPMEncoder(this);
//start the generation of the signal through the speakers
int result=ppmencoder.startGeneration();
if (result!=0){
//error occoured, something went wrong
AlertDialog.Builder alert = new AlertDialog.Builder(this);
alert.setTitle("Error");
alert.setMessage("Error during audio signal generation. Error Number " + result);
alert.setPositiveButton("Ok", new DialogInterface.OnClickListener() {
public void onClick(DialogInterface dialog, int whichButton) {
}
});
alert.show();
}
stick1VerticalLabel = (TextView) findViewById(R.id.stick1VerticalLabel);
stick1HorizontalLabel = (TextView) findViewById(R.id.stick1HorizontalLabel);
stick2VerticalLabel = (TextView) findViewById(R.id.stick2VerticalLabel);
stick2HorizontalLabel = (TextView) findViewById(R.id.stick2HorizontalLabel);
// referring as others views
joystickLeft = (JoystickView) findViewById(R.id.joystickViewLeft);
joystickRight = (JoystickView) findViewById(R.id.joystickViewRight);
// Listener of events, it'll return the angle in graus and power in percents
// return to the direction of the moviment
joystickLeft.setOnJoystickMoveListener(new OnJoystickMoveListener() {
@Override
public void onValueChanged(int angle, int power, int direction) {
//scompose the vector
float stickVertical=(float) Math.sin((Math.PI/180) * angle)*power; //values between +100 and -100
stickVertical=stickVertical+(float)100; //values between 0 and 200
stickVertical=(float)stickVertical*(float)((float)255/(float)200); //values between 0 and 255
float stickHorizontal=(float) Math.cos((Math.PI/180) * angle)*power; //values between +100 and -100
stickHorizontal=stickHorizontal+(float)100; //values between 0 and 200
stickHorizontal=stickHorizontal*(float)((float)255/(float)200); //values between 0 and 255
stick1VerticalLabel.setText("channel1:" + String.valueOf(stickVertical));
stick1HorizontalLabel.setText("channel2:" + String.valueOf(stickHorizontal));
ppmencoder.setChannelValue(1, stickVertical);
ppmencoder.setChannelValue(2, stickHorizontal);
}
}, JoystickView.DEFAULT_LOOP_INTERVAL);
joystickRight.setOnJoystickMoveListener(new OnJoystickMoveListener() {
@Override
public void onValueChanged(int angle, int power, int direction) {
//scompose the vector
//scompose the vector
float stickVertical=(float) Math.sin((Math.PI/180) * angle)*power; //values between +100 and -100
stickVertical=stickVertical+(float)100; //values between 0 and 200
stickVertical=(float)stickVertical*(float)((float)255/(float)200); //values between 0 and 255
float stickHorizontal=(float) Math.cos((Math.PI/180) * angle)*power; //values between +100 and -100
stickHorizontal=stickHorizontal+(float)100; //values between 0 and 200
stickHorizontal=stickHorizontal*(float)((float)255/(float)200); //values between 0 and 255
stick2VerticalLabel.setText("channel3:" + String.valueOf(stickVertical));
stick2HorizontalLabel.setText("channel4:" + String.valueOf(stickHorizontal));
ppmencoder.setChannelValue(3, stickVertical);
ppmencoder.setChannelValue(4, stickHorizontal);
}
}, JoystickView.DEFAULT_LOOP_INTERVAL);
}
@Override
protected void onDestroy() {
super.onDestroy();
int result=ppmencoder.stopGeneration();
if (result!=0){
AlertDialog.Builder alert = new AlertDialog.Builder(this);
alert.setTitle("Error");
alert.setMessage("Error while stopping the audio generation. Error number " + result);
alert.setPositiveButton("Ok", new DialogInterface.OnClickListener() {
public void onClick(DialogInterface dialog, int whichButton) {
}
});
alert.show();
}
}
}
file PPMEncoder.java (this is the class requested on the original question)
package com.tr3ma.PPMtestProject;
import java.util.ArrayList;
import android.content.Context;
import android.media.AudioFormat;
import android.media.AudioManager;
import android.media.AudioTrack;
import android.os.AsyncTask;
public class PPMEncoder
{
public int SAMPLE_RATE = 44100;
public int ppmFrameBufferSize = (int)(SAMPLE_RATE * 0.0225); // 22KHz * 22,5ms that it is the duration of a frame ppm
public int audioBufferSize;
private ArrayList<Float> channelValues;
AudioManager audioManager;
StreamPPMSignalTask streamPPMSignalTask;
private boolean started;
public PPMEncoder(Context context)
{
audioManager = (AudioManager)context.getSystemService(Context.AUDIO_SERVICE);
//set volume to max
//audioManager=(AudioManager) context.getSystemService(Context.AUDIO_SERVICE);
int tmpVol = audioManager.getStreamMaxVolume(AudioManager.STREAM_MUSIC);
audioManager.setStreamVolume(AudioManager.STREAM_MUSIC, tmpVol, 0);
channelValues = new ArrayList<Float>(8);
for (int i = 0; i < 8; i++) {
channelValues.add((float)0.68181818);
}
}
public int startGeneration()
{
try {
audioBufferSize = AudioTrack.getMinBufferSize(SAMPLE_RATE,
AudioFormat.CHANNEL_OUT_MONO,
AudioFormat.ENCODING_PCM_16BIT)*2;
if (audioBufferSize<=0 ) return -2;
started = true;
streamPPMSignalTask = new StreamPPMSignalTask();
streamPPMSignalTask.execute();
return 0;
} catch (Exception e) {
e.printStackTrace();
}
return -1;
}
public int stopGeneration()
{
try {
started = false;
streamPPMSignalTask.cancel(true);
streamPPMSignalTask = null;
return 0;
} catch (Exception e) {
e.printStackTrace();
}
return -1;
}
private int timeToSamples(float time)
{
//time is expressed in milliseconds
return (int)Math.round(time * 0.001 * SAMPLE_RATE);
}
public void setChannelValue(int channel, float value)
{
channelValues.set(channel - 1, (float)0.68181818+(float)1.0 * ((float)value/(float)255));
}
public int setSamplingRate(int freq) {
//we can change the sampling frequency in case the default one is not supported
try {
SAMPLE_RATE=freq;
ppmFrameBufferSize = (int)(SAMPLE_RATE* 0.0225); // 22KHz * 22,5ms
audioBufferSize = AudioTrack.getMinBufferSize(SAMPLE_RATE,
AudioFormat.CHANNEL_OUT_MONO,
AudioFormat.ENCODING_PCM_16BIT) * 2;
if (audioBufferSize<=0 ) return -2;
started=false;
stopGeneration();
startGeneration();
//frame=new byte[streamBufferSize];
return 0;
} catch (Exception e) {
e.printStackTrace();
}
return -1;
}
public class StreamPPMSignalTask extends AsyncTask<Void, Double, Void>
{
@Override
protected Void doInBackground(Void... arg0) {
AudioTrack ppmTrack = new AudioTrack(AudioManager.STREAM_MUSIC, SAMPLE_RATE, AudioFormat.CHANNEL_OUT_MONO,
AudioFormat.ENCODING_PCM_16BIT, audioBufferSize, AudioTrack.MODE_STREAM);
//set volume of audioplayer to max
ppmTrack.setStereoVolume((float) 1.0, (float) 1.0);
if (ppmTrack.getPlayState() != AudioTrack.PLAYSTATE_PLAYING) {
ppmTrack.play();
}
//feed the speakers with our audio, by continuously send the PPM frame
int tempBound;
while (started) {
try {
short[] frame = new short[ppmFrameBufferSize];
int i = 0;
tempBound = i + timeToSamples((float)0.3);
for (;i < tempBound; i += 1) {
frame[i] = Short.MIN_VALUE;
}
for (int channel = 0; channel < 8; channel++) {
tempBound = i + timeToSamples(channelValues.get(channel));
for (;i < tempBound; i += 1) {
frame[i] = Short.MAX_VALUE;
}
tempBound= i + timeToSamples((float)0.3);
for (;i < tempBound; i += 1) {
frame[i] = Short.MIN_VALUE;
}
}
for (;i < frame.length; i += 1) {
frame[i] = Short.MAX_VALUE;
}
//send the frame
ppmTrack.write(frame, 0, frame.length);
} catch (Exception e) {
e.printStackTrace();
}
}
return null;
}
}
}
End notes:
1) as you can see the 2 joysticks moves only 4 channels, but it is clear that you can add another 2 joystick controls on the activity in order to move all 8 channels.
2) credit goes to this site where you can see how it is made the joystickControl http://www.zerokol.com/2012/03/joystickview-custom-android-view-to.html in case you want to customize it. I wish to do it but i had no time. today i spent the entire day to write this post.