The L3G4200D is a 3-axis angular rate sensor, aka gyro/gyroscope with a user selectable 250, 500 or 2000º/Sec scale. I was about to write about what a gyro is, but Sparkfun has done a really great job of that, so to quote them:
Gyroscopes measure angular velocity, how fast something is spinning about an axis. If you’re trying to monitor the orientation of an object in motion, an accelerometer may not give you enough information to know exactly how it’s oriented. Unlike accelerometers gyros are not affected by gravity, so they make a great complement to each other. You’ll usually see angular velocity represented in units of rotations per minute (RPM), or degrees per second (°/s). The three axes of rotation are either referenced as x, y, and z, or roll, pitch, and yaw.
Hooking It Up
The L3G4200D has a lot of pins on it because it supports both SPI and I2C but also has some other features as well such as programmable interrupts. We are going to go as simple with this as possible.
The L3G4200D supports both SPI and I2C, but we are just going to talk I2C here. I2C is a 2-wire serial connection, so you just need to connect the SDA (Data) and SCL (Clock) lines to your Arduino for communication. On your Arduino (everything but the mega) SDA is on analog pin 4, and SCL is on analog pin 5. On an arduino mega, SDA is digital 20, and SCL is digital 21.
Code
The code for this is a little complex mainly because it is a digital device. But I tried to simplify it as much as possible for you. You may have noticed that Sparkfun already had a code example written. Yep… And part of this code is based on that. I actually decided to write new code for 2 reasons. 1: Their code is CreativeCommons licensed. I like MIT better because you are more free to do what you need with it. 2: I like I2C better than SPI – Why? 2 less wires!
This code just outputs the x,y,z axis angular rate (in deg/sec) in the serial terminal. Simple as that.
According to the data sheet, this is all correct. But when the sensor is sitting still and is set to 2000º/sec, I am seeing readings of 0-70 on all 3 axises. I know gyros drift, but this seems weird. If someone knows what is going wrong here please let me know.
Read more: L3G4200D Tripple Axis Gyroscope + Arduino