I am using android.os.Handler's “postDelayed” method to turn ON and OFF a relay. There are 2 runnable - one for sending ON command and another for sending OFF command. The relay needs to be kept on for fixed ms and turned OFF for fixed ms again.
I referred this old android post http://android-developers.blogspot.in/2007/11/stitch-in-time.html to send repeating commands to the relay
The start command needs to be sent at the same time from different devices - each connected to a different relay. So the effect should be that all relays should turn ON at the same time.
I ensure that the command is sent at the same time from each device, using GPS time sync on all devices. Once all devices are GPS time synced, I send ON command at start of second for the first time and then add the fixed delays to the postDelay methods in both runnables.
I still notice that the relays are not turned ON at the same time the first time itself. I notice a delay upto 1 sec.
I need to know how reliable is "postDelayed" method? Can I trust it for a precision upto 5 ms? Is there a more reliable way to send a repeating command at a fixed delay?
Here is part of the code
public class RelayAsyncTask extends AsyncTask<Void, Integer, Boolean>
{
private Activity context = null;
private Handler handler = null;
private Runnable offRunnable,onRunnable;
@Override
protected void onPreExecute()
{
handler = new Handler();
onRunnable = new Runnable() {
@Override
public void run() {
new RelayTurnOnAsyncTask().executeOnExecutor(AsyncTask.THREAD_POOL_EXECUTOR, null);
publishProgress(1); // used to display on UI that a command has been sent
handler.postDelayed(offRunnable, 500);
}
};
offRunnable = new Runnable() {
@Override
public void run() {
new RelayTurnOffAsyncTask().executeOnExecutor(AsyncTask.THREAD_POOL_EXECUTOR, null);
publishProgress(2); // used to display on UI that a command has been sent
handler.postDelayed(onRunnable, 1000);
}
};
super.onPreExecute();
}
@Override
protected Boolean doInBackground(Void... params) {
try {
// Code to calculate diff when first ON command should be sent
.
.
handler.postDelayed(onRunnable, diff);
}
catch(Exception e)
{
e.printStackTrace();
}
return null;
}
@Override
protected void onProgressUpdate(Integer... values) {
switch (values[0]) {
case 0:
{
break;
}
case 1:
{ //code to update UI
.
.
break;
}
case 2:
{ //code to update UI
. .
.
break;
}
default:
break;
}
}
@Override
protected void onPostExecute(Boolean result) {
super.onPostExecute(result);
}
}
I also notice a delay upto 10 ms when RelayTurnOnAsyncTask().executeOnExecutor(AsyncTask.THREAD_POOL_EXECUTOR, null) is called.
