Android提高之模拟信号示波器的实现

前面简单地介绍了Android程序开发中AudioRecord和AudioTrack的使用，这次再结合SurfaceView实现一个Android版的手机模拟信号示波器。最近物联网炒得很火，作为手机软件开发者，如何在不修改手机硬件电路的前提下实现与第三方传感器结合呢？麦克风就是一个很好的ADC接口，通过麦克风与第三方传感器结合，再在软件里对模拟信号做相应的处理，就可以提供更丰富的传感化应用。

先来看看本文程序运行的效果图(屏幕录像截图的速度较慢，真机实际运行起来会很流畅)：

本文程序使用8000hz的采样率，对X轴方向绘图的实时性要求较高，如果不降低X轴的分辨率，程序的实时性较差，因此程序对X轴数据缩小区间为8倍～16倍。由于采用16位采样，因此Y轴数据的高度相对于手机屏幕来说也偏大，程序也对Y轴数据做缩小，区间为1倍～10倍。在SurfaceView的OnTouchListener方法里加入了波形基线的位置调节，直接在SurfaceView控件上触摸即可控制整体波形偏上或偏下显示。

main.xml源码如下：

ClsOscilloscope.java是实现示波器的类库，包含AudioRecord操作线程和SurfaceView绘图线程的实现，两个线程同步操作，代码如下：

package com.testOscilloscope;
import java.util.ArrayList;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.graphics.Rect;
import android.media.AudioRecord;
import android.view.SurfaceView;
public class ClsOscilloscope {
 private ArrayList inBuf = new ArrayList();
 private boolean isRecording = false;// 线程控制标记
 /**
 * X轴缩小的比例
 */
 public int rateX = 4;
 /**
 * Y轴缩小的比例
 */
 public int rateY = 4;
 /**
 * Y轴基线
 */
 public int baseLine = 0;
 /**
 * 初始化
 */
 public void initOscilloscope(int rateX, int rateY, int baseLine) {
 this.rateX = rateX;
 this.rateY = rateY;
 this.baseLine = baseLine;
 }
 /**
 * 开始
 * 
 * @param recBufSize
 *      AudioRecord的MinBufferSize
 */
 public void Start(AudioRecord audioRecord, int recBufSize, SurfaceView sfv,
  Paint mPaint) {
 isRecording = true;
 new RecordThread(audioRecord, recBufSize).start();// 开始录制线程
 new DrawThread(sfv, mPaint).start();// 开始绘制线程
 }
 /**
 * 停止
 */
 public void Stop() {
 isRecording = false;
 inBuf.clear();// 清除
 }
 /**
 * 负责从MIC保存数据到inBuf
 * 
 * @author GV
 * 
 */
 class RecordThread extends Thread {
 private int recBufSize;
 private AudioRecord audioRecord;
 public RecordThread(AudioRecord audioRecord, int recBufSize) {
  this.audioRecord = audioRecord;
  this.recBufSize = recBufSize;
 }
 public void run() {
  try {
  short[] buffer = new short[recBufSize];
  audioRecord.startRecording();// 开始录制
  while (isRecording) {
   // 从MIC保存数据到缓冲区
   int bufferReadResult = audioRecord.read(buffer, 0,
    recBufSize);
   short[] tmpBuf = new short[bufferReadResult / rateX];
   for (int i = 0, ii = 0; i < tmpBuf.length; i++, ii = i
    * rateX) {
   tmpBuf[i] = buffer[ii];
   }
   synchronized (inBuf) {//
   inBuf.add(tmpBuf);// 添加数据
   }
  }
  audioRecord.stop();
  } catch (Throwable t) {
  }
 }
 };
 /**
 * 负责绘制inBuf中的数据
 * 
 * @author GV
 * 
 */
 class DrawThread extends Thread {
 private int oldX = 0;// 上次绘制的X坐标
 private int oldY = 0;// 上次绘制的Y坐标
 private SurfaceView sfv;// 画板
 private int X_index = 0;// 当前画图所在屏幕X轴的坐标
 private Paint mPaint;// 画笔
 public DrawThread(SurfaceView sfv, Paint mPaint) {
  this.sfv = sfv;
  this.mPaint = mPaint;
 }
 public void run() {
  while (isRecording) {
  ArrayList buf = new ArrayList();
  synchronized (inBuf) {
   if (inBuf.size() == 0)
   continue;
   buf = (ArrayList) inBuf.clone();// 保存
   inBuf.clear();// 清除
  }
  for (int i = 0; i < buf.size(); i++) {
   short[] tmpBuf = buf.get(i);
   SimpleDraw(X_index, tmpBuf, rateY, baseLine);// 把缓冲区数据画出来
   X_index = X_index + tmpBuf.length;
   if (X_index > sfv.getWidth()) {
   X_index = 0;
   }
  }
  }
 }
 /**
  * 绘制指定区域
  * 
  * @param start
  *      X轴开始的位置(全屏)
  * @param buffer
  *      缓冲区
  * @param rate
  *      Y轴数据缩小的比例
  * @param baseLine
  *      Y轴基线
  */
 void SimpleDraw(int start, short[] buffer, int rate, int baseLine) {
  if (start == 0)
  oldX = 0;
  Canvas canvas = sfv.getHolder().lockCanvas(
   new Rect(start, 0, start + buffer.length, sfv.getHeight()));// 关键:获取画布
  canvas.drawColor(Color.BLACK);// 清除背景
  int y;
  for (int i = 0; i < buffer.length; i++) {// 有多少画多少
  int x = i + start;
  y = buffer[i] / rate + baseLine;// 调节缩小比例，调节基准线
  canvas.drawLine(oldX, oldY, x, y, mPaint);
  oldX = x;
  oldY = y;
  }
  sfv.getHolder().unlockCanvasAndPost(canvas);// 解锁画布，提交画好的图像
 }
 }
}

testOscilloscope.java是主程序，控制UI和ClsOscilloscope，代码如下：

package com.testOscilloscope;
import android.app.Activity;
import android.graphics.Color;
import android.graphics.Paint;
import android.media.AudioFormat;
import android.media.AudioRecord;
import android.media.MediaRecorder;
import android.os.Bundle;
import android.view.MotionEvent;
import android.view.SurfaceView;
import android.view.View;
import android.view.View.OnTouchListener;
import android.widget.Button;
import android.widget.ZoomControls;
public class testOscilloscope extends Activity {
  /** Called when the activity is first created. */
 Button btnStart,btnExit;
 SurfaceView sfv;
  ZoomControls zctlX,zctlY;
  
  ClsOscilloscope clsOscilloscope=new ClsOscilloscope();
  
 static final int frequency = 8000;//分辨率
 static final int channelConfiguration = AudioFormat.CHANNEL_CONFIGURATION_MONO;
 static final int audioEncoding = AudioFormat.ENCODING_PCM_16BIT;
 static final int xMax = 16;//X轴缩小比例最大值,X轴数据量巨大，容易产生刷新延时
 static final int xMin = 8;//X轴缩小比例最小值
 static final int yMax = 10;//Y轴缩小比例最大值
 static final int yMin = 1;//Y轴缩小比例最小值
 
 int recBufSize;//录音最小buffer大小
 AudioRecord audioRecord;
 Paint mPaint;
  @Override
  public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.main);
    //录音组件
 recBufSize = AudioRecord.getMinBufferSize(frequency,
  channelConfiguration, audioEncoding);
 audioRecord = new AudioRecord(MediaRecorder.AudioSource.MIC, frequency,
  channelConfiguration, audioEncoding, recBufSize);
 //按键
 btnStart = (Button) this.findViewById(R.id.btnStart);
 btnStart.setOnClickListener(new ClickEvent());
 btnExit = (Button) this.findViewById(R.id.btnExit);
 btnExit.setOnClickListener(new ClickEvent());
 //画板和画笔
 sfv = (SurfaceView) this.findViewById(R.id.SurfaceView01); 
 sfv.setOnTouchListener(new TouchEvent());
    mPaint = new Paint(); 
    mPaint.setColor(Color.GREEN);// 画笔为绿色 
    mPaint.setStrokeWidth(1);// 设置画笔粗细 
    //示波器类库
    clsOscilloscope.initOscilloscope(xMax/2, yMax/2, sfv.getHeight()/2);
    
    //缩放控件，X轴的数据缩小的比率高些
 zctlX = (ZoomControls)this.findViewById(R.id.zctlX);
 zctlX.setOnZoomInClickListener(new View.OnClickListener() {
  @Override
  public void onClick(View v) {
  if(clsOscilloscope.rateX>xMin)
   clsOscilloscope.rateX--;
  setTitle("X轴缩小"+String.valueOf(clsOscilloscope.rateX)+"倍"
   +","+"Y轴缩小"+String.valueOf(clsOscilloscope.rateY)+"倍");
  }
 });
 zctlX.setOnZoomOutClickListener(new View.OnClickListener() {
  @Override
  public void onClick(View v) {
  if(clsOscilloscope.rateXyMin)
   clsOscilloscope.rateY--;
  setTitle("X轴缩小"+String.valueOf(clsOscilloscope.rateX)+"倍"
   +","+"Y轴缩小"+String.valueOf(clsOscilloscope.rateY)+"倍");
  }
 });
 
 zctlY.setOnZoomOutClickListener(new View.OnClickListener() {
  @Override
  public void onClick(View v) {
  if(clsOscilloscope.rateY 
 

希望本文实例对于读者进行Android项目开发能起到一定的借鉴与帮助作用。