Guide to gyro and accelerometer with Arduino including Kalman filtering

system · October 4, 2011, 7:28am

did you use atan2 insteadt of atan? in scilab atan = atan2 ... sry to confuse you

Lauszus · October 4, 2011, 8:15am

Yes I used atan (or arctan) as the document says at page 13

system · October 16, 2011, 11:04pm

@ Lauszus Im trying to use your code with an I2c gyro and accelerometer but the sensitivity is given in lowest significant bit, would you know how to apply this?
Im using
gyro ITG 3200 with sensitivity 14.375 LSB/(º/s)
accelerometer BMA180 the sensitivity varies with the G but at 1 g is 8192 LSB/g

Lauszus · October 16, 2011, 11:20pm

@cristo829
Hi
You should have a look at the dialog I had with "Kashif" starting at this link: Guide to gyro and accelerometer with Arduino including Kalman filtering - #111 by system - Sensors - Arduino Forum. He is using the same gyro as you (ITG3200), but not the same accelerometer though (ADXL345). This is the IMU: SparkFun 6 Degrees of Freedom IMU Digital Combo Board - ITG3200/ADXL345 - SEN-10121 - SparkFun Electronics.

If you follow the dialog, I think you will get it working. Just remember to change the values for the accelerometer!

Alternative send him a PM and ask for his code..

If you need more help, just send another reply and I will try to help you as best I can

system · October 17, 2011, 2:31am

Great thanks

antonro1 · October 17, 2011, 12:10pm

I'm using this sensor combination (FreeIMU 0.3.5MS) also - you can just feed the raw values from the BMA accelerometer into the filter. There's no need to scale the sensitivity, although it makes no difference if you do. Also, if you're using up to 4G sensitivity, there's no need to calibrate (ie subtracting the offsets). The BMA seems to have a fairly accurate calibration I've found.

system · October 19, 2011, 2:43pm

So you changed this:
gyroX = analogRead(gX);
gyroXrate = (gyroX-gyroZeroX)/1.0323;//(gyroX-gryoZeroX)/Sensitivity Sensitivity = 0.00333/3.31023=1.0323
gyroXangle += gyroXratedtime/1000;

to this?

(read x value on i2c gyro)
gyroXrate = (gyroX-gyroZeroX)
gyroXangle += gyroXrate*dtime/1000;

Im building a qudcopter, how many Gs do you think is a good idea to use on the BMA? Also, have you programmed the Magnetometer on your IMU im having some trouble with the tilt compensation, my measurement varies within 10 degrees when i tilt it which is finw for me, except when i tilt it to one specific side when i tilt it that way it varies something like 40 degrees is this normal?
Thanks for your help

antonro1 · October 19, 2011, 2:57pm

I'm using 3G for my quad, this seems to be a good compromise between pitch/roll accuracy and sensitivity to noise. If you try 1.5G, you might find it too sensitive to vibrations.

I have used the mag, I have to calibrate it by working out the offsets. The best accuracy I've got has been a calibration with the sensor in place and all four motors running (without props on obviously). I get pretty good stable results with the MARG algorithm as part as the FreeIMU library, but I haven't recently tried tilt compensation calculations with my current offsets so can't really comment on how well this works.

Your gyro code looks ok to me.

cristo829:
So you changed this:
gyroX = analogRead(gX);
gyroXrate = (gyroX-gyroZeroX)/1.0323;//(gyroX-gryoZeroX)/Sensitivity Sensitivity = 0.00333/3.31023=1.0323
gyroXangle += gyroXratedtime/1000;

to this?

(read x value on i2c gyro)
gyroXrate = (gyroX-gyroZeroX)
gyroXangle += gyroXrate*dtime/1000;

Im building a qudcopter, how many Gs do you think is a good idea to use on the BMA? Also, have you programmed the Magnetometer on your IMU im having some trouble with the tilt compensation, my measurement varies within 10 degrees when i tilt it which is finw for me, except when i tilt it to one specific side when i tilt it that way it varies something like 40 degrees is this normal?
Thanks for your help

system · October 21, 2011, 3:01am

Thanks AntR ill try that

system · October 27, 2011, 8:00am

Hello everyone --

I'm really glad to find this thread so active. I'm currently working on a project that involved tracking the orientation and position of an object.

I've got an ADXL345 accelerometer, ITG-3200 gyro and an HMC5883L magnetometer.

I've gotten Fabio Varesano's awesome code working which is giving me great position information.

But I'm hoping someone on this thread can point me to some code that I can use to get a good measurement of velocity so I can calculate position.

Thanks in advance.

Lauszus · October 27, 2011, 8:10pm

I would be possible using the accelerometers and then multiply it with one g and the delta time. But you have to do some math to compensate for rotation. Please post the code if you get it working

system · November 6, 2011, 9:40am

Hey,

I'm using this LISY300AL Gyro: http://www.sparkfun.com/datasheets/Sensors/LISY300AL.pdf
But i cant get a precise data..

Here is my calculation:

    sensitivity = 0.716454545;
    gyroAdc = analogRead(0);
    if(abs(gyroAdc - gyroZero) <= Threshold)
      gyroAdc = gyroZero;
    gyroRate = (gyroAdc-gyroZero)/sensitivity;
    gyroRotation=gyroRotation+gyroRate*dtime1/1000;
    gyroAngle = abs((gyroRotation - 360 * ceil(gyroRotation / 360))); // Round up between 0-360
    dtime = millis() - stime;
    stime = millis();

I dont get a precise angle, i move my object 90 degrees but the gyro drifts too much so it showes something else...
Maybe i'm doing something wrong ? or i should just add an Accelerometer to make it more precise ?

Lauszus · November 6, 2011, 3:16pm

First of all, how did you calculate your sensitivity?
If you use either 3.3 or 5 volt as reference, it's either:
0.0033/3.31023=1.023
or
0.0033/51023=0.67518
As the sensor has a sensitivity of 3.3 mV/ °/s
Or do you use a different reference? As i can calculate you use 4.711952801 volt as reference (0.0033/4.711952801*1023=0.716454545).

Why do you need this line:

gyroAngle = abs((gyroRotation - 360 * ceil(gyroRotation / 360))); // Round up between 0-360

What you call "gyroRotation", is actually the angle

For more precision use integration.
Something like this would work:

#define OFFSET 0.0005

gyroRaw = analogRead(0);
gOffset = OFFSET * gyroRaw + (1-OFFSET) * gOffset;
gyroSpeed = (gyroRaw - gOffset)/sensitivity;

gyroAngle += gyroSpeed*dtime/1000;

See this page for more information: http://www.hitechnic.com/blog/gyro-sensor/htway/

Regards
Lauszus

system · November 6, 2011, 4:30pm

Lauszus:
First of all, how did you calculate your sensitivity?
If you use either 3.3 or 5 volt as reference, it's either:
0.0033/3.31023=1.023
or
0.0033/51023=0.67518
As the sensor has a sensitivity of 3.3 mV/ °/s
Or do you use a different reference? As i can calculate you use 4.711952801 volt as reference (0.0033/4.711952801*1023=0.716454545).

Why do you need this line:
gyroAngle = abs((gyroRotation - 360 * ceil(gyroRotation / 360))); // Round up between 0-360
What you call "gyroRotation", is actually the angle

For more precision use integration.
Something like this would work:
#define OFFSET 0.0005

gyroRaw = analogRead(0);
gOffset = OFFSET * gyroRaw + (1-OFFSET) * gOffset;
gyroSpeed = (gyroRaw - gOffset)/sensitivity;

gyroAngle += gyroSpeed*dtime/1000;




See this page for more information: http://www.hitechnic.com/blog/gyro-sensor/htway/

Regards
Lauszus

Hey, thanks for the replay.

I'm using 3.3v so i changed the sensitivity to 1.023, now the numbers are even less precise.
the gyroZero after calibration is around 325, and the gyro goes about -+300.

I removed the gyroAngle = abs((gyroRotation - 360 * ceil(gyroRotation / 360))); // Round up between 0-360

When i use this:

#define OFFSET 0.0005

gyroRaw = analogRead(0);
gOffset = OFFSET * gyroRaw + (1-OFFSET) * gOffset;
gyroSpeed = (gyroRaw - gOffset)/sensitivity;

gyroAngle += gyroSpeed*dtime/1000;

The numbers goes crazy and keep going up even when the gyro doesn't move.

Bottom line:
Sensitivity = 1.023 - When i move my object 90 Degrees, the gyro showes 50-55 Degrees.
Sensitivity = 0.716454545 - When i move my object 90 Degrees, the gyro showes 83-88 Degrees.

Those drifts just getting worse every move so after few movements the gyro isn't helpfull.

Any ideas ?

Lauszus · November 6, 2011, 6:00pm

Have you remembered to connect 3.3 Volt to the VREF pin on the Arduino?

Regards
Lauszus

system · November 7, 2011, 7:43am

Lauszus:
Have you remembered to connect 3.3 Volt to the VREF pin on the Arduino?

Regards
Lauszus

I used this guide: GyroLISY300AL \ Learning \ Wiring
I connected the VCC on the gyro to the Arduino 3.3v pin.

Is that what you ment ?

Lauszus · November 7, 2011, 9:29am

No you have to connect 3.3V to the VREF/AREF pin on the Arduino.

Regards
Lauszus

system · November 8, 2011, 10:42am

Hey, thanks alot for you replays i learn alot of new stuff and you are being very helpfull

So in my Gyro i have VCC & GND pin, i connected the VCC to the Arduino 3.3v pin and the GND to one of the GND pins on the Arduino.
And i connected the OUT pin of the gyro to the Analog0 pin on the Arduino.

I use this external Power Supply

As you can see i'm giving 12v to the Arduino, and the Fixed volts are set to 3.3v and connected stright to the AREF pin and one of the GND pins on the arduino.

Now i changed my sensitivity back to 1.023, and added analogReference(EXTERNAL); to the setup() in my code.

You can see the purple black and red goes to the gyro, the big connector that connected to the 7,8,9 digitals is a Servo controller, and the 2 pins from the external supply to the AREF & GND.

Here is the code, every one milliseconds i call this:

void gyroTest()
{
    if(gyroInit) {
      finalGyroAngle = calculateGyroAngle(0);
      Serial.println(finalGyroAngle);
    }
}

float calculateGyroAngle(int pin)
{
    gyroAdc = calibrateGyro(0);
    if(abs(gyroAdc - gyroZero) <= Threshold)
      gyroAdc = gyroZero;
    gyroRate = (gyroAdc-gyroZero)/sensitivity;
    gyroRotation+=gyroRate*dtime/1000;
    unsigned long t = millis();
    dtime = t - stime;
    stime = t;
    return gyroRotation;
}

void InitGyro(int pin)
{
  Serial.println("Calibrating Gyro...");
  sensitivity = 1.023; //0.692454545; //0.716454545;
  gyroAdc = 0;
  gyroRate = 0;
  gyroRotation = 0;
  gyroAngle = 0;
  gyroZero = calibrateGyro(pin);
  Serial.print("Gyro Calibrated: ");
  Serial.println(gyroZero);
}

int calibrateGyro(int pin)
{
  long resultGyro = 0;
  for(int i=0;i<100;i++)
  {
    resultGyro += analogRead(pin);
    delay(0.5);
  }
  resultGyro = resultGyro/100;
  return resultGyro;
}

Am i doing everything ok ?

Lauszus · November 8, 2011, 10:50am

Glad to see you figured it out
What are you going to use the setup for? Controlling the servo or something like that?

Regards
Lauszus

system · November 8, 2011, 4:22pm

Hey, i still didn't solve it

I'll explain why the setup for and what is my problem.
As you see i have a WiFi shield connected, i send him commands to spin the servo that is connected to a arm that the gyro is on so the gyro spins with it.

I want to tell the servo to spin 90 degrees, and then go back to 0 degrees, and do that in a loop.
That's why i need the Gyro for, to get the degrees.

My problem is that after 2-3 time it goes to 90 then 0 the drifting goes crazy and it goes to 110 then -20...
So my problam still isn't solved.

I posted all my setup so you can see if i'm doing everything right, i hope you can help me figure it out.

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Guide to gyro and accelerometer with Arduino including Kalman filtering

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