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...:yikes:

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.slotT oIndex(slot));
tSPI.writeChannels_SCLK_Channel(DigitalModule.rema pDigitalChannel(clockPin-1));

tSPI.writeChannels_MOSI_Module(DigitalModule.slotT oIndex(slot));
tSPI.writeChannels_MOSI_Channel(DigitalModule.rema pDigitalChannel(dataOutPin-1));

tSPI.writeChannels_MISO_Module(DigitalModule.slotT oIndex(slot));
tSPI.writeChannels_MISO_Channel(DigitalModule.rema pDigitalChannel(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...:D

John K. Erdelyan
Lead Mentor & Programming Mentor
Team 2910