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:

Re: Analog-to-Digital Converter Code
 

wow thanks allot!

Re: Analog-to-Digital Converter Code
 

I've updated the ADC code to version 0.3. The new version uses the "special event trigger" functionality of the CCP2 module to automatically start an analog to digital conversion without software intervention. This new version generates half of the interrupts/sec of version 0.2. As always, the code can be found here: http://kevin.org/frc

-Kevin

Re: Analog-to-Digital Converter Code
 

Well, I finally posted the ADC and Gyro code for the 2006 robot controller. Sorry about the delay, but I ran into a nasty bug that caused me to spend a few days in the fourth and fifth levels of programmer hell. The bug was in the design of the PIC18F8722 (yes, a bug in the sillicon) and I had to figure out what was going on. Anyway, the gyro code works really, really well with the gyro in the kit of parts. The accelerometers also work really well, but I need to do more testing before I unleash that code.


-Kevin

Re: Analog-to-Digital Converter Code
 

Let's suppose there are four analog signals being sampled and "buffered" by your code. The gyro is running on ADC_CH0 and the other three channels are for other devices. How do we know when the gyro specifically has new data available? I saw the ~update_count~ variable, but it seemed to just indicate when any new sample is available, not when the sample for a specific channel is. Am I going to have to modify your code (maybe add an array of update_counts, with each index correspondent with the channel's freshness of data?) to allow this functionality, or is it already there and I'm just not seeing it?

Re: Analog-to-Digital Converter Code
 

The update flag only gets incremented after all enabled ADC channels have been refreshed. You can get less latency (if that's what you're after) by doing the modification you described, or by just moving the gyro to the last enabled channel and continue using Get_ADC_Result_Count().

-Kevin

Re: Analog-to-Digital Converter Code
 

Hi Kevin...

Excellent code. I'm trying to get some early Auto-Heading code testing done using an existing Robot. I was hoping I could use the team's little 2003 EDU robot as a test platform.

I'm an experienced embedded programmer, but new to the IFI hardware.

I tried deploying your gyro code on the small EDU controller. I discovered that when I included the new ADC module I got a program run error light, so I dropped back to the standard iti_utilities code for the ADC conversion. (I assumed a basic hardware incompatibility....)

My only problem is that now I'm not sure where to put the call to Process_Gyro_Data().

I'd like to put it in User_Routines_Fast.c but I don't have your ADC code installed so I don't know when the converters have got new values. D'oh.

Am I flogging a dead horse here, or is there a simple way to use the standard IFI analog utilities to drive your Gyro code? I'm only using a single analog channel (for the Gyro) so that may simplify things. I don't need fully calibrated data for my initial testing... I just need it to basically run. If I can get the calls IN, I can get the rest to work.

Thanks for your time.
Phil.

Re: Analog-to-Digital Converter Code
 

Phil,

Gyro code for the EDU-RC can be found on my website.

-Kevin

Re: Analog-to-Digital Converter Code
 

Oops.

I'm in "drinking from a fire-hose" mode and never seem to look in the right place for information. Just when I think I've downloaded enough... I find more.. After posting, I discovered your adc_readme file which let me go through and add your stuff to our teem's prior EDU-RC code. Now I don't get an error & the gyro seems to be working as with the 2006RC.

Now with this new information I can double check against your webiste archives if need be.

Thanks.
I'll look harder next time.
Phil

Re: Analog-to-Digital Converter Code
 

Hello all,

First off, I want to thank kevin for writing this code.
This *should* help us use all those sensors we just looked at and admired last year as rookies.

Unfortunately, our team is not gifted with a large number (read - 0) dedicated programmers. So I'm not too far ahead of the kids at this point which disappoints me because I cant really help them the way I should be (when I barely know anything myself).

But I did read all the readme.txt files associated with the code Kevin's supplied, and I have 2 main questions which deal with getting the code and hardware on the same page.

1. After I hook up my PWMs to the sensor (take your pick) and plug it into the RC's analog input, how do I make the code know which port I'm looking at?

and

2. How do I test / troubleshoot / even see the output from the sensor?
Is there some easy way to use a "print to a .txt file" or something? (something I'd try on a PC) Better yet, what is the BEST way to get all the information? I'm seeing outputs in some of these posts mentioning the same kind of scaling that you see when you output to one of the motors. So should I find some way to get the info back to the dashboard (which I still need to set up). Even with that, we need to integrate (for many of the sensors) and seeing the value at any one time wont tell us too much.

Hope I'm not being too redundant or posting in the wrong place. If any of my questions indicate that I'm just fundamentally wrong, point that out too, please.

It's all for the kids and the future,
Aaron

Re: Analog-to-Digital Converter Code
 

Kevin,

The adc_readme.txt says to remove the call to Set_Number_of_Analog_Channels() in user_routines.c. But the user_routines.c file included in the same zip (frc_adc.zip) still has it in. Same situation in the user_routines.c file in the frc_gyro.zip.

So, should the call remain as is, or be commented out?

Thanks

Re: Analog-to-Digital Converter Code
 

Hmmm... I guess I should follow my own instructions <grin>. Actually, it doesn't matter as long as the call to Initialize_ADC() happens after the call to Set_Number_of_Analog_Channels() (it does in all the ADC-related code I've posted). If you're happy with my code, I'd just remove the call to Set_Number_of_Analog_Channels(), otherwise just comment it out in case you want to fall back to IFI's code.

-Kevin

Re: Analog-to-Digital Converter Code
 

Okay, I know this is getting kind of abstract, and not truly necessary to a "black box" understanding of this code, but how exactly does oversampling work? I looked it up on wikipedia, and all i got was more confused. I understand that is is supposed to give more precision, but I really don't understand how.

Thanks.

Re: Analog-to-Digital Converter Code
 

Oversampling is essentially taking a number of samples and averaging them. If you average four samples, you get the equivalent of two more bits of resolution, but it takes four times as long to get the value. It trades time for precision.

Re: Analog-to-Digital Converter Code
 

so then does it take values 4x faster? It seems like taking the average over 4 program cycles would make it less precise.

Re: Analog-to-Digital Converter Code
 

Yes, it samples faster than the rate the data is being sent.

I have another question for Kevin (of course, I'm trying to optimize everything, but I don't want to make a bad move while doing this):

Is there a specific reason for switching from doing both the initiation of and saving of an ADC sample in the timer interrupt? I remember in last year's gyro code that both functions were done in the same place, whereas now you are using both the timer interrupt, and the ADC interrupt to take the samples. Is it safe to kinda shift the ADC functionality to the timer interrupt and reduce the extra overhead by removing the ADC interrupt altogether? Or do the two of them together execute faster, somehow, than the single timer?

Before you:
- Started the initial A/D conversion in Initialize_XXXX()
- Saved the value at the start of the timer2 interrupt
- Did the if/else/etc to put the value in the right place
- Started another A/D conversion by setting the GO bit.
- Exited the timer2 interrupt.

And if I get the go ahead, I'll just do this again.

Re: Analog-to-Digital Converter Code
 

The following whitepaper goes much more in depth and may make more sense: http://www.chiefdelphi.com/forums/pa...le&paperid=234

Re: Analog-to-Digital Converter Code
 

I have downloaded the FRC_GYRO code, compiled and linked it in MPLAB, and it controls the gyro great, thanks.

When I copy the FRC_Library into my 2006 project code (to update from the 8250 (2005) to the 8722 (2006) controller, I am getting a link error saying that symbol ifi_packet_num1 has multiple definitions. I was able to determine that there is a copy of ifi_utilities.o (where ifi_packet_num1 is defined) in the FRC_Library (that wasn't there in 2005). I was able to work around the problem by removing ifi_utilites.c from the project, and it linked fine.

My question is: Is there some setting I am missing in my project that would allow the linker to use the first instance of the object file it comes across versus including all versions. I see ifi_utilities.c in the frc_gyro (gyro.mcp) project, and the link works correctly. Since I don't modify ifi_utilities.c my work around shouldn't be a problem, but I would like to know why one project will link correctly, while another one won't.

Thanks, Mark

Re: Analog-to-Digital Converter Code
 

Wow, that really explained it well. Thanks.

Re: Analog-to-Digital Converter Code
 

As I was waiting for your reply I took a look at the spec sheet for the PIC18f8722. It says there is a set delay of at least 2.5 microseconds that has to exist between the setting of an analog channel and the initiation of its conversion (to allow the sample and hold capacitor to start charging). Is this the reason for the seperation of the two actions?

I also see the following: which makes it seem as though the PIC could implement a delay by itself. But taking another look at your code, I noticed that you enabled manual acquisition (ADCON2<5:3> = 0). Did you find the PIC to be unreliable in this area, or have I totally missed the point?

I'll wait for your feedback before continuing.

Re: Analog-to-Digital Converter Code
 

This is a great question. When I modified the code last Summer to separate the ADC and gyro functionality, I added the ability to sample multiple ADC channels using a simple round-robin algorithm. If you read the pic18f8520 data sheet you'll notice the second paragraph on page 217 which states:

"After the A/D module has been configured as desired, the selected channel must be acquired before the conversion is started...To determine acquisition time, see Section19.1 “A/D Acquisition Requirements”. After this acquisition time has elapsed, the A/D conversion can be started."

What this means is that you need to allow sufficient time for the sample-and-hold capacitor to charge between the time you change the channel and can actually start the conversion. Providing this delay within an ISR is, to say the least, un-cool. My solution was to start the conversion using the timer 2 ISR and manage data and change the ADC channel in the ADC ISR. The sample-and-hold capacitor then has ample time to charge between the ADC and timer 2 ISRs. This is how the currently posted code works.

The pic18f8722, used in the current robot controller, has added circuitry to automatically provide the acquisition delay before conversion begins (see page 277 of the p18f8722 data sheet). In the next revision of the ADC code I suspect that I'll be able to do away with the ADC interrupt and do everything in the timer 2 ISR. Perhaps this would be a good programming exercise for you?

-Kevin

Re: Analog-to-Digital Converter Code
 

ok, great!

I'll modify your code for use now, and then I'll swap in your next revision when you make it gold.

Thanks for the feedback.

Re: Analog-to-Digital Converter Code
 

For some reason our team is having great difficulty in getting the analog inputs to work, no matter what we plug into the inputs or print. We have initialized them and receive no errors yet no inputs are received. We have attempted testing a gyro, accelerometer, ultrasonic sensor, and variable resistor (potentiometer) but none have made a difference.

Re: Analog-to-Digital Converter Code
 

There is a #define statement in adc.h that is something like NUMBER_OF_CHANNELS (I'm going from memory here, so I don't know exactly what the statement actually defines). Is that defined as 16? We had some analog input trouble last year when we only had 1 channel active and were trying to tune four PID loops using pots that were connected to analog ports that weren't enabled, which didn't work very well, but caused no compile-time errors.

Re: Analog-to-Digital Converter Code
 

Actually that wasn't the problem, but we seem to have fixed it. Our problem actually was that the interrupt Timer_4_ISR was defined in both adc.c, adc.h and timers.c and .h. No errors appeared but it didnt allow inputs.

Re: Analog-to-Digital Converter Code
 

This is documented in the readme.txt file included with the software. Specifically, items 2 and 3:

-Kevin

Re: Analog-to-Digital Converter Code
 

Hi Kevin, We have recently come to realize that the p1_y and p1_x ADCs are somewhat noisy. The output value varies randomly maybe about +/-10 of 127 when the joystick is connected, but not touched. Does your code address this problem? We were trying to work around the problem using a comb digital filter.

Thanks,
Windell

Re: Analog-to-Digital Converter Code
 

No, that code runs on the PIC inside the operator interface, which I didn't write. I would try using a running average of 2-4 samples to see if it quiets down.

-Kevin

Re: Analog-to-Digital Converter Code
 

Hello Kevin
When our team is using your FRC gyro code. there seems to be a problem. The motors are twitching. That is the arm and shoulder motors are coming back but are not staying in there.
Can u please tell us what to do about that. We caliberated the victors and checked the victors and checked the voltages. But when we use the default code without gyros the code works fine.

Please let us know what is happenning.

Thank you
Srinivas

Re: Analog-to-Digital Converter Code
 

What PWMs are your victors connected to? PWMs 13-16 are controlled by the user processor and subject to glitches under high load when using IFI's Generate_PWMs function. If you move those motors to another PWM or use Kevin's replacement PWM code, it should work better.