Android – IOIO – RC Servo (or ESC)

This is a sequel to my first Hello World example with the IOIO / Android setup….

Android + IOIO controlling a RC servo

It simply adds a RC servo that is controlled by the same seekBar that controls the brightness of the LED.

Here’s a quick and pretty good explanation of how the standard RC protocol (just a specific case of PWM really !) works :
http://www.societyofrobots.com/robotforum/index.php?topic=4299.0
To sum it up, the RC signal is a 50Hz signal, so 20ms period, out of which it is HIGH between 1 and 2ms. So the duty cycle of the signal has to be between 5 and 10%, with the neutral being around 7.5%.

Here’s a video showing the theory working:

And here’s the Android code.

2 things to notice:

1. _servo = ioio_.openPwmOutput(5, 50);  that starts a PWM signal on pin 5, with a 20ms period (corresponding to what the standard RC signal expects)
2. _servo.setDutyCycle(0.05f + _varValue * 0.05f); which basically varies the duty cyle between 5 and 10% (depending on the position of the seekBar) so that the HIGH period of the signal will vary between 1 and 2 milliSeconds (again corresponding to that a RC servo/ESC or anything else, expects)

package org.trandi.helloioio;

import ioio.examples.hello.R;
import ioio.lib.api.PwmOutput;
import ioio.lib.api.exception.ConnectionLostException;
import ioio.lib.util.AbstractIOIOActivity;
import android.os.Bundle;
import android.widget.SeekBar;
import android.widget.SeekBar.OnSeekBarChangeListener;
import android.widget.TextView;

public class MainActivity extends AbstractIOIOActivity {
private SeekBar _seekBarVar;
private TextView _varField;
private volatile float _varValue;

/**
* Called when the activity is first created. Here we normally initialize our GUI.
*/
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
_seekBarVar = (SeekBar) findViewById(R.id.seekBarVar);
_varField = (TextView) findViewById(R.id.textViewVarVal);

_seekBarVar.setMax(100);

_seekBarVar.setOnSeekBarChangeListener(new OnSeekBarChangeListener() {
@Override
public void onStopTrackingTouch(SeekBar seekBar) {
}

@Override
public void onStartTrackingTouch(SeekBar seekBar) {
}

@Override
public void onProgressChanged(SeekBar seekBar, int progress, boolean fromUser) {
_varValue = (float)progress / (float)_seekBarVar.getMax();
_varField.setText(String.valueOf(_varValue));
}
});
}

/**
* This is the thread on which all the IOIO activity happens. It will be run
* every time the application is resumed and aborted when it is paused. The
* method setup() will be called right after a connection with the IOIO has
* been established (which might happen several times!). Then, loop() will
* be called repetitively until the IOIO gets disconnected.
*/
class IOIOThread extends AbstractIOIOActivity.IOIOThread {
// The on-board LED
private PwmOutput _led;
// a attached servo
private PwmOutput _servo;

/**
* Called every time a connection with IOIO has been established.
* Typically used to open pins.
*
* @throws ConnectionLostException When IOIO connection is lost.
*
* @see ioio.lib.util.AbstractIOIOActivity.IOIOThread#setup()
*/
@Override
protected void setup() throws ConnectionLostException {
_led = ioio_.openPwmOutput(0, 300);
_servo = ioio_.openPwmOutput(5, 50); // 20ms periods
}

/**
* Called repetitively while the IOIO is connected.
*
* @throws ConnectionLostException When IOIO connection is lost.
*
* @see ioio.lib.util.AbstractIOIOActivity.IOIOThread#loop()
*/
@Override
protected void loop() throws ConnectionLostException {
_servo.setDutyCycle(0.05f + _varValue * 0.05f);
_led.setDutyCycle(1 - _varValue);
}
}

/**
* A method to create our IOIO thread.
*
* @see ioio.lib.util.AbstractIOIOActivity#createIOIOThread()
*/
@Override
protected AbstractIOIOActivity.IOIOThread createIOIOThread() {
return new IOIOThread();
}
}