Electronic – L3G4200D Gyro Sensor – Measuring Angle

gyrosensor

I am making an IMU for 6DOF which has L3G4200D 3-Axis Digital Gyroscope.

I've checked so many Blogs, Forums, Application notes and have programmed accordingly to get the proper reading/information from my gyro.

Though I am very near to solve it – a single problem has made me mad since last two nights!
I've 16 bit digit – 1 signed bit + 15 bit value

Suppose I want to measure an angle with respect to X-axis at 2000 dps, for that I am doing the following:

while(1)
{
     for(g=39;g<42;g++)
    {
        r = I2CRegRead(I2C0_MASTER_BASE, 0x68, g);  // read the reg. no. g
            switch (g)
            {
                case 40:       
                l = r;             // LSB part of X_Gyro
                    break;
            case 41:
                h = r;            // MSB part of x_Gyro
                x = 0;
                x = h<<8;
                x = x|l;
                x = x*70/1000;
                        UARTprintf("Gyro_X : %5d\n\r",x);
                    break;
                }
         }
}

I am getting some values most probably <800 when I move gyro in counter clock direction with respect to X-axis and getting >4000 for the opposite direction!!

I want to have positive angle values while rotating it on counter clockwise direction and negative angle values for the clock wise direction… For that what I should add on my calculations?? [Angles should be in degrees 1 to 180 & (-1) to (-180)]

// in code 0.007 is in mdps which is the value of each LSB of gyro's data

What I should add in could and why I am having >4000 & <800 values right now?

Could anyone please help me with this?

Thank you so much for your valuable time.

Best Answer

First, you could use something like this to get your value into a proper signed integer:

uint8_t xl = ...;
uint8_t xh = ...;
int16_t x = *(int8_t *)(&xh);
x *= (1 << 8);
x |= xl;

But x is just a value in Degree per Second. To get your current orientation as angle, you have to integrate this value over time, which will add a lot of drift. To compensate for this, you could then filter it with accelerometer data (PDF!).

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