Magnetic Encoder Programming Question\Consult

[jerdelyan]

Ok, it is 11:30pm. I have been working on this dilemma off and on since 10am this morning; researching the WPI Library, USFirst Forum, FIRST Forge, Chief Delphi, and NI Communities and i have not been able to figure out if there is a class designed to communicate with the magnetic encoders over PWM. I am looking for something along the lines of the Jaguar class (used to control the Jaguar motor controllers) or the existing encoder class (optical only or requires the usage of 2 channels A and B) but to use the single PWM unfiltered out put from the Magnetic Encoder that was included in the KOP. I have not been able to find anything to date... If there is something out there please let me know...

With the understanding that there is nothing that I can find that exists already I am looking at creating something to do this task for me. I am thinking of using a Digital Input class with the Get() function (not sure if it will work or what it will 'get' me) or an interrupt in combination with a timer to time the rise and fall of the PWM signal to calculate the time of the pulse.

The only other idea i have could be to use the Counter class with the Timer class to accomplish a similar effect.

Any way it is after midnight now and my pregnant wife is telling me to shut the light off and go to sleep. So i look forward to your ideas...!

Thanks for your help in this mater...
John Erdelyan
Team 2910 Jack in the Bot

[Greg McKaskle]

The LabVIEW example for the magnetic encoder treats the sensor output as analog. It takes the default analog values and multiplies by 72. It also shows a simple filter to handle rollover.

If you have LV installed, you might run the example so you can debug the wiring and such.

Greg McKaskle

[charrisTTI]

I spent the better part of a day looking at the magnetic encoder I/O options. We ruled out the analog angle output because of the slow response at the rollover point. I did not give the PWM output much thought. I tried two different approaches for which I am including code samples. The first reads the data digitally using the SPI support and the second uses two analog channels to read the sin/cos outputs (be sure to remove the solder jumper to enable these ports).

Here is the digital one using SPI:

/*
 * To change this template, choose Tools | Templates
 * and open the template in the editor.
 */

package edu.wpi.first.wpilibj;

import edu.wpi.first.wpilibj.fpga.tSPI;

/**
 *
 * @author charris
 */
public class AS5030FourWireSPI extends SensorBase {

    public class AS5030Result
    {
        public double angle;
        public int agc;
    }


    tSPI spi;
    DigitalModule module;
    int slot;
    int clockPin;
    int dataOutPin;
    int dataInPin;
    int chipSelectPin;


    public AS5030FourWireSPI( int slotParam, int clockPinParam, int dataOutPinParam, int dataInPinParam, int chipSelectPinParam )
    {
        slot = slotParam;
        clockPin = clockPinParam;
        dataOutPin = dataOutPinParam;
        dataInPin = dataInPinParam;
        chipSelectPin = chipSelectPinParam;
        
        // get our module
        module = DigitalModule.getInstance(slot);

        // create SPI instance
        //spi = new tSPI();

        // allocate our pins
        module.allocateDIO(clockPin, false);
        module.allocateDIO(dataOutPin, false);
        module.allocateDIO(dataInPin, true);
        module.allocateDIO(chipSelectPin, false);

        // setup for SPI
        tSPI.writeChannels_SCLK_Module(DigitalModule.slotToIndex(slot));
        tSPI.writeChannels_SCLK_Channel(DigitalModule.remapDigitalChannel(clockPin-1));

        tSPI.writeChannels_MOSI_Module(DigitalModule.slotToIndex(slot));
        tSPI.writeChannels_MOSI_Channel(DigitalModule.remapDigitalChannel(dataOutPin-1));

        tSPI.writeChannels_MISO_Module(DigitalModule.slotToIndex(slot));
        tSPI.writeChannels_MISO_Channel(DigitalModule.remapDigitalChannel(dataInPin-1));
    }

    public void initialize()
    {
        // set chip select low to start
        module.setDIO(chipSelectPin, true);

        // data is valid on rising edge of clock
        tSPI.writeConfig_DataOnFalling(false);

        // set the bit order
        tSPI.writeConfig_MSBfirst(true);

        tSPI.strobeReset();
        tSPI.strobeClearReceivedData();
    }

    public AS5030Result getData( )
    {
        // select the chip
        module.setDIO(chipSelectPin, false);

        // write the 5 bit command
        // set the width
        tSPI.writeConfig_BusBitWidth(5);

        // write the data to load
        tSPI.writeDataToLoad(0x1F);

        // strobe out the data
        tSPI.strobeLoad();

        // wait for completion
        while( !tSPI.readStatus_Idle() )
        {
            java.lang.Thread.yield();
        }

        // change back to 16 bits
        tSPI.writeConfig_BusBitWidth(16);
        // clear the data to load
        tSPI.writeDataToLoad(0x0);

        // clear received data
        tSPI.strobeClearReceivedData();

        // strobe in the data
        tSPI.strobeLoad();


        // wait for completion
        //while( !tSPI.readStatus_Idle() )
        while( tSPI.readReceivedElements() == 0 )
        {
            java.lang.Thread.yield();
        }

        // strobe in the received data
        tSPI.strobeReadReceivedData();

        // read the data
        long rawData = tSPI.readReceivedData();

        // deselect the chip
        module.setDIO(chipSelectPin, true);

        AS5030Result result = new AS5030Result();

        long rawAngle = rawData & 0xFF;

        int agc = (int)((rawData >> 8) & 0x3F);

        result.angle = (double)rawAngle * 360.0 / 256.0;
        result.agc = agc;
        
        return result;
    }
}

Here is the dual analog input approach:

/*
 * To change this template, choose Tools | Templates
 * and open the template in the editor.
 */

package edu.wpi.first.wpilibj;

import  com.sun.squawk.util.MathUtils;

/**
 *
 * @author charris
 */
public class AS5030DualAnalog extends SensorBase implements PIDSource {

    private static final double biasVoltage = 2.25;
    private AnalogChannel sinChannel;
    private AnalogChannel cosChannel;

    public AS5030DualAnalog( int slotParam, int sinChannelParam, int cosChannelParam)
    {
        sinChannel = new AnalogChannel( slotParam, sinChannelParam );
        cosChannel = new AnalogChannel( slotParam, cosChannelParam );
    }

    protected double getCos()
    {
        return cosChannel.getVoltage() - biasVoltage;
    }

    protected double getSin()
    {
        return sinChannel.getVoltage() - biasVoltage;
    }

    public double getAngle()
    {
        // calculate the angle
        double theta = MathUtils.atan2( getSin(), getCos() );
        // convert to degrees
        return Math.toDegrees(theta) + 180.0;
    }

    /**
     * Get the angle of the encoder for use with PIDControllers
     * @return the current angle according to the encoder
     */
    public double pidGet() {
        return getAngle();
    }


}

Give them a try.

[jerdelyan]

Thanks for the help on this. In looking at your code it appears that there are some other functions out there that may work for me as well.

I noticed that this code is in Java but i hope that the functions are names are similar (i remember reading that somewhere). If i get something to work today i will post the code later tonight...!

JE

[jerdelyan]

Ok, so i wanted to get the PWM working without modifing the chip any more (we already burnt one up). so i played with the code and was able to get code working to sample the PWM on a digital input port of the digital sidecar. i have attached the example below in c++.

void OperatorControl(void)
{
	GetWatchdog().SetEnabled(false);
	timeStart = 0.0;
	timeEnd = 0.0;
	avgPulseTime = 0.0;
	pulseCounter = 0;
	positionDegree = 0;
	const UINT32 slot = 4;
	char *c = NULL;
	DigitalModule *dm = DigitalModule::GetInstance(slot);// (slot);		
	DriverStationLCD *dsLCD = DriverStationLCD::GetInstance();
	dm->AllocateDIO(1,true);
	//dsLCD->UpdateLCD();
		
	while (IsOperatorControl())
	{	
		if(dm->GetDIO(1) == 1)
		{
			//start the timer and get the time
			tim1.Start();
			timeStart=tim1.Get();

			while(dm->GetDIO(1) == 1) //repeat until there is a falling edge
			{
				Wait(.000001);  //Pause for 1usec
			}
			timeEnd=tim1.Get();
			tim1.Stop(); //stop the timer
			if(0 < (timeEnd - timeStart) < .000578)  //filter out noise
			{
				avgPulseTime += (timeEnd-timeStart); //sum up all of the pulses
				pulseCounter++;
			}
		}
		//looking to average 10 pulses together
		if (pulseCounter == 10)
		{
			avgPulseTime /= pulseCounter;
			avgPulseTime *= 1000000;
			positionDegree = avgPulseTime * 360 / 578;
			pulseCounter = 0;
			//display on the screen
			sprintf(c,"%03d",positionDegree);
			dsLCD->Printf(dsLCD->kUser_Line4,1,c);
			dsLCD->UpdateLCD();
			tim1.Reset();
			avgPulseTime = 0.0;
			*c = NULL;
		}	
		Wait(.0000005);
	}
}

I am basically sampling the code at 1usec and capturing the time of the pulse. from there i can take the different times and convert it to degrees. it is then displayed on the dashboard...
I hope that this can help somone else who is thinking of doing the same thing...

John K. Erdelyan
Lead Mentor & Programming Mentor
Team 2910