Chief Delphi - Analog-to-Digital Converter Code

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Analog-to-Digital Converter Code

For those who might be interested, I've just posted new analog-to-digital converter interface code for IFIs robot controllers. A few advantages of using this software include parallel, non-blocking operation of the ADC hardware, precise control over the sampling period, which is important for signal processing and control applications and the ability to make measurements with greater precision using a technique called oversampling. 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.

-Kevin

Here's the readme file:

Code:

 

The source code in adc.c/.h contains software to setup and run

your robot controllers analog-to-digital converter in the 

background. A few advantages of using this software include 

parallel, non-blocking operation of the ADC hardware, precise 

control over the sampling period, which is important for signal 

processing and control applications and the ability to make more 

precise measurements using oversampling. Number of channels, 

sample rate and oversampling parameters can be changed by 

editing adc.h and re-compiling.

 

This software makes the assumption that when it's running, it 

solely controls the analog to digital conversion hardware.

 

WARNING: The higher sampling rates can place quite a load on

the robot controllers CPU. If you get the red-light-of-death

or notice any general wackiness in the operation of your

robot, first try a lower sampling rate to determine if this

is the problem. In general, you should select the lowest

sampling rate that meets your performance criteria.

 

This source code will work with the Robovation (A/K/A EDU-RC) 

robot controller and the FIRST Robotics robot controller.

 

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 with your robot controller:

 

1) A #include statement for the adc.h header file must be 

included at the beginning of each source file that calls the 

functions in adc.c. The statement should look like this: 

#include "adc.h".

 

2) Initialize_ADC() must be called from user_routines.c/

User_Initialization().

 

3) On the EDU-RC, all analog inputs must be configured as 

INPUTs in user_routines.c/User_Initialization().

 

4) The call to Set_Number_of_Analog_Channels() must be removed

or commented out in user_routines.c/User_Initialization().

 

5) The timer 2 interrupt handler, Timer_2_Int_Handler(), and

ADC interrupt handler, ADC_Int_Handler(), must be installed in

User_Routines_Fast.c/InterruptHandlerLow(). See the included 

copy of User_Routines_Fast.c to see how this is done.

 

6) Define the number of analog channels that you'd like this

software to track by opening adc.h and following the embedded

instructions above #define NUM_ADC_CHANNELS.

 

7) For advanced users, analog channels can be oversampled to

decrease noise and gain resolution in your analog measurements.

The oversampling ratio can be changed from the default x16

by commenting-out the line #define ADC_SAMPLES_PER_UPDATE_16

found in adc.h and then removing the // from in front of one

of the other options. Measurement range and resolution can be 

determined from this table:

 

ADC Samples Effective
Averaged         Bits of        Measurement Voltage
Per Update Resolution         Range         Per Bit
___________ __________ ___________ _________
         1                 10                0-1023         4.88 mV
         2                 10                0-1023         4.88 mV
         4                 11                0-2047         2.44 mV
         8                 11                0-2047         2.44 mV
        16                 12                0-4095         1.22 mV
        32                 12                0-4095         1.22 mV
        64                 13                0-8191         610 uV
128                 13                0-8191         610 uV
256                 14                0-16383         305 uV
 

8) Finally, pick the master sample rate by selecting one

of the available rates found in adc.h. The update rate can

be determined using this formula:

Update Rate = 

        Sample Rate / (Samples Per Update * Number Of Channels)

 

****************************************************************

 

Here's a description of the functions in adc.c:

 

Get_ADC_Result_Count()

This function returns an unsigned char containing the number 

of ADC updates generated since Reset_ADC_Result_Count() or 

Initialize_ADC() were called. Use this function to determine

when fresh analog to digital conversion data is ready.

 

Reset_ADC_Result_Count()

This function can be called to reset the ADC update counter

to zero.

 

Get_ADC_Result()

This function can be called to retreive analog to digital

conversion results. Call this function with an unsigned char

containing the ADC channel you'd like data from. This function

will return an unsigned int with the last conversion result.

 

Convert_ADC_to_mV()

This function converts the value generated by the ADC to

millivolts.

 

Initialize_ADC()

This function initializes the ADC hardware and software. It 

should be called from user_routines.c/User_Initialization().

Once called, analog to digital conversions will automatically

take place in the background.

 

Disable_ADC()

This function disables the ADC hardware and software. To

minimize the load on the microcontroller, this function should 

be called when the ADC functionality is no longer needed.

 

Initialize_Timer_2()

This function initializes and starts timer 2, which initiates

a new analog to digital conversion each time the timer 2

interrupt service routine is called. This is called by

Initialize_ADC() above and shouldn't be called directly.

 

Disable_Timer_2()

This function is called from Disable_ADC() to disable timer 2 

and shouldn't be called directly.

 

Timer_2_Int_Handler()

This function is automatically called when timer 2 causes an

interrupt and shouldn't be called directly. New analog to

digital conversions are initiated from this function.

 

ADC_Int_Handler()

This function is automatically called when new analog to

digital conversion data is ready and shouldn't be called

directly.