For those who might be interested, I’ve just posted updated gyroscope interface code for IFI’s robot controllers. The code has been significantly reworked to use the new ADC interface code, which allows the programmer to use other analog sensors alongside a gyroscope without affecting the performance or operation of the gyroscope. In addition, significant performance improvements can be realized using the new oversampling and deadband features. The code can be found here: http://kevin.org/frc. As always, if you find a bug in the code or a problem with the documentation, please let me know.
Here’s the readme file:
The source code in gyro.c/.h contains a driver and supporting software to interface a variety of inexpensive gyros to your robot controller. This software was tested with Analog Devices' ADXRS401EB, ADXRS150EB and ADXRS300EB gyros. Data sheets for these devices are included. By default, this software is configured to work with a ADXRS150EB gyro, sampling at 800Hz, downconverting to an update rate of 50Hz by averaging sixteen samples per update. These parameters can be changed by editing gyro.h and/or adc.h. Version 0.5 of the gyro interface software has been altered to use the ADC interface provided by adc.c/.h. This change allows the programmer to use additional ADC channels for other analog sensors without affecting the performance or operation of your gyro. See the documentation included with adc.c/.h for information on how to use this new functionality. Another new feature is the ability to specify a measurement deadband centered about the gyro bias. ADC measurements within this deadband will not be used to calculate the gyro angle or angular rate. This feature can have a significant impact at minimizing short-term drift just after a bias calculation has taken place. To use this feature, follow the instructions embedded within gyro.h. This source code will work with the Robovation (A/K/A EDU-RC) robot controller and the FIRST Robotics robot controller. Wiring-up the ADXRS401EB, ADXRS150EB and ADXRS300EB gyro evaluation boards is straightforward: Grab a PWM cable and cut off the male end and strip the three wires back a centimeter or so. With a low wattage soldering iron, solder the white wire to the RATEOUT pin, solder the black wire to the AGND pin, the red wire to the AVCC pin, and finally connect a jumper wire between the AVCC and PDD pins. Plug the female end into one of the robot controller's analog inputs. These gyro evaluation boards can be purchased from analog devices ([www.analog.com](http://www.analog.com/)), and Digi-Key ([www.digikey.com](http://www.digikey.com/)). Another great source for Analog Devices gyros is SparkFun Electronics ([www.sparkfun.com](http://www.sparkfun.com/)). For optimum performance, you'll need to calibrate the scaling factor to match that of your gyro. One way to calibrate your gyro is to mount it very securely to a hefty, square or rectangular object. Mounting the gyro to a hefty object will help dampen higher frequency vibrations that can adversely effect your measurements. Place the mounted gyro against another square object and start the included demonstration software. To get good results, the mount must be absolutely still when the "Calibrating Gyro Bias..." message appears on the terminal screen. After a few seconds, the gyro angular rate and angle will be sent to the terminal screen. If the angle drifts rapidly while the mounted gyro is motionless, you need to restart the software to acquire a new gyro bias measurement. Again, gyros are very sensitive and must be still while the bias is calculated. Once the gyro is running with little drift, rotate the mount 180 degrees and note the reported angle. If the angular units are set to tenths of a degree, the ideal reported angle is 1800. If set to milliradians, the ideal angle 1s 3142 (Pi times a thousand). For every tenth of a percent that the angle is high, decrease the GYRO_CAL_FACTOR numerator by one. Conversly, for every tenth of a percent low, increase the numerator by one. Repeat until you're satisfied with the accuracy. The included project files were built with MPLAB version 7.20. If your version of MPLAB complains about the project version, the best thing to do is just create a new project with MPLAB's project wizard. Include every file except: FRC_alltimers.lib and ifi_alltimers.lib and you should be able to build the code. **************************************************************** Eight things must be done before this software will work correctly on your robot controller: 1) The gyro's rate output is wired to one of the analog inputs of your robot controller and gyro.h/#define GYRO_CHANNEL is updated with the analog channel your gyro is attached to. 2) A #include statement for the gyro.h header file must be included at the beginning of each source file that calls the functions in gyro.c. The statement should look like this: #include "gyro.h". 3) Initialize_Gyro() must be called from user_routines.c/ User_Initialization(). 4) You must select the gyro you're using from a list in gyro.h and if needed, remove the // in front of its #define. 5) The default angular unit is milliradians. If desired, this can be changed to tenths of a degree by editing gyro.h 6) A gyro bias calculation must take place using the functions Start_Gyro_Bias_Calc() & Stop_Gyro_Bias_Calc() described below. This must be done several hundred milliseconds after the gyro powers-up and is allowed to stabilize. 7) For optimal performance, you'll need to calibrate the gyro scaling factor using the instructions above or those included in gyro.h. 8) Follow the instructions found in adc_readme.txt for installation instructions. **************************************************************** Here's a description of the functions in gyro.c: Initialize_Gyro() This function initializes the gyro software. It should be called from user_routines.c/User_Initialization(). Get_Gyro_Rate() This function returns the current angular rate of change in units of milliradians per second. If desired, the angular unit can be changed to tenths of a degree per second by modifying the angular units #define entry in gyro.h Get_Gyro_Angle() This function returns the change in heading angle, in milliradians, since the software was initialized or Reset_Gyro_Angle() was called. If desired, the angular unit can be changed to tenths of a degree by modifying the angular units #define entry in gyro Start_Gyro_Bias_Calc() Stop_Gyro_Bias_Calc() These functions start/stop a new gyro bias calculation. For best results, Start_Gyro_Bias_Calc() should be called about a second after the robot powers-up and while the robot is perfectly still with all vibration sources turned off (e.g., compressor). After at least a second (longer is better), call Stop_Gyro_Bias_Calc() to terminate the calibration. While a calibration is taking place, gyro rate and angle are not updated. Once calibrated, a call to Reset_Gyro_Angle() should take place. Get_Gyro_Bias() This function returns the current calculated gyro bias. For extra precision, this software internally maintains a gyro bias value that is the sum of GYRO_SAMPLES_PER_UPDATE samples of the gyro's analog output. By default, GYRO_SAMPLES_PER_UPDATE is set to a value of eight in gyro.h Set_Gyro_Bias() This function can be called to manually set the gyro bias. For extra precision, this software internally maintains a gyro bias value that is the sum of GYRO_SAMPLES_PER_UPDATE samples of the gyro's analog output. By default, GYRO_SAMPLES_PER_UPDATE is set to a value of eight in gyro.h Reset_Gyro_Angle() This function resets the integrated gyro heading angle to zero. Process_Gyro_Data() This function should be called when the ADC software reports that new gyro data is available. Ideally this should be done within the user_routines_fast.c/Process_Data_From_Local_IO() function. See the enclosed copy of user_routines_fast.c for an example of how to do this.