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1. 

   luver26
   Member

   Hi, I'm new with the forum but i have a question to ask:
   I wrote this code for the arduino board:
   '
   #include <SD.h>

   int pulsante = 5;

   int marker = 4;

   int minimo = 6;

   int massimo = 14;

   String data = "";

   String markers ="";

   int parametro,conteggio=0;

   int dato,righe=3,i=2;

   char name[] = "Test1.csv",dir[]= "Test1";

   String s;

   boolean premuto = true;

   unsigned lun;

   void setup()
   {
   pinMode(53, OUTPUT);

   if (!SD.begin(4)) {

   return;
   }

   while(SD.exists(dir))/
   {
   dir[4] = '';
   s = dir;
   s += i;
   s.toCharArray(dir,s.length()+1);
   i++;
   }

   i = 2;

   if (!SD.mkdir(dir)){

   return;
   }
   s = dir;
   s += "/";
   s += name;
   s.toCharArray(name,s.length()+1);
   s = dir;
   lun = s.length();

   }

   void loop()
   {
   pinMode(pulsante,INPUT);

   while(digitalRead(pulsante)==LOW){
   ;//null
   }
   for (int corrente =minimo; corrente<=massimo; corrente++)
   pinMode(corrente, INPUT);//pone i pin dal n°6 al n°14 in lettura
   while(SD.exists(name))
   {
   name[lun + 5] = '';
   s = name;
   s += i;
   s += ".csv";
   s.toCharArray(name,s.length()+1);
   i++;
   }
   File lettura1 = SD.open(name, O_CREAT | O_APPEND | O_WRITE);

   if (lettura1) { //se è stato possibile creare il file stampa del testo
   lettura1.println("Nuova Sessione:");
   lettura1.println("CH1");
   lettura1.print("\t");
   lettura1.print("CH2");
   lettura1.print("\t");
   lettura1.print("CH3");
   lettura1.print("\t");
   lettura1.print("CH4");
   lettura1.print("\t");
   lettura1.print("CH5");
   lettura1.print("\t");
   lettura1.print("CH6");
   lettura1.print("\t");
   lettura1.print("CH7");
   lettura1.print("\t");
   lettura1.print("CH8");
   lettura1.print("\t");
   }

   while(digitalRead(pulsante)==HIGH){

   parametro=analogRead(61);
   dato=(parametro*500)/1023;
   lettura1.println(parametro);

   parametro=analogRead(62);
   dato=(parametro*500)/1023;
   lettura1.println(parametro);

   parametro=analogRead(63);
   dato=(parametro*500)/1023;
   lettura1.println(parametro);

   parametro=analogRead(64);
   dato=(parametro*500)/1023;
   lettura1.println(parametro);

   parametro=analogRead(65);
   dato=(parametro*500)/1023;
   lettura1.println(parametro);

   parametro=analogRead(66);
   dato=(parametro*500)/1023;
   lettura1.println(parametro);

   parametro=analogRead(67);
   dato=(parametro*500)/1023;
   lettura1.println(parametro);

   parametro=analogRead(68);
   ato=(parametro*500)/1023;
   lettura1.println(parametro);

   lettura1.println();
   if(premuto){
   if(digitalRead(marker)==HIGH){
   premuto = false;

   }
   }
   else{
   if(digitalRead(marker)==LOW)
   premuto=true;

   }

   }

   lettura1.close();

   }
   '
   Basically it reads analog signals form 8 channels and prints the results on a csv file in a SD card with the Arduino SD shield,the thing is i can only get 516 Samples/sec with the best optimization i was able to obtain.
   So now i was thinking about moving the code to the maple board but since it's an university project i need to be sure of the sampling rate i can obtain with the maple board befre actually buying it;So i would like to ask if someone could give my code a try(i understand only a few changes need to be made) and let me know how is the Sampling rate(possibly with a Serial monitor screenshot of the resoult of an inceasing variable after 10 seconds of execution),I hope someone can help me.
   Thanks anyways

   Posted 3 years ago #
2. 

   gbulmer
   Moderator

   Have you tried finding out where the bottleneck is?

   I'd expect an Arduino to be able to take almost 10,000 ADC samples/second.
   For example, have you commented out all of the lettura1.println() to see if it is the file I/O?

   Also, an int on an Arduino is 16 bits (http://arduino.cc/en/Reference/Int) so:
   

   parametro=analogRead(...);
   dato=(parametro*500)/1023;

   will produce nonsense for any value bigger than 65.

   Posted 3 years ago #
3. 

   mbolivar
   LeafLabs

   hi luver26! welcome to the forum. please read the guidelines for posting:

   http://forums.leaflabs.com/topic.php?id=994

   in particular, please don't post long code listings directly into the forum. use a pastebin service instead.

   Posted 3 years ago #
4. 

   luver26
   Member

   The parametro variable is supposed to be a double type,i may have copyed it wrong form the ino file when i was trying to get an higher sampling rate,by the way,yes the arduino can do 9600 ADC samples/sec but on 8 channels 9600/8=1200,and moreover with the data saving on the SD device i can only get 500 samples/sec which is too low for my purposes,the low rate is caused by the file.print function which automaticly does 6 flushes everytime it writes on the file,but i can't do otherways i tried to save the 8 ch reads on an array and then writing it but for some reason i can only get arrays of char or int data types,also there is another function(file.write) which is a bit faster but requires numeric reads to be converted in char data so it's pointless;that's why i tought the maple will work considering a rate 48 times higher than the arduino board(http://forums.leaflabs.com/topic.php?id=154 with the modify) i just needed to be sure.

   Posted 3 years ago #
5. 

   crenn
   Moderator

   If you want an array of chars, I'd look into using something such as sprintf and then writing it out.

   EDIT:

   char array[255];
double value=9.81;
sprintf(array,"The earth's field is %lf m/s^2", value);
card.write(array);

   Posted 3 years ago #
6. 

   luver26
   Member

   I only wanted to know which sampling rate could my code obtain with the maple boar,that's what i need

   Posted 3 years ago #
7. 

   gbulmer
   Moderator

   luver26 - getting high sample rate, and reliable data is more than just analogRead speed.

   The STM32F103xB datasheet explains what the Maple is capable of:
   http://www.st.com/internet/mcu/product/164487.jsp

   We might be able to help you if you explain what it is you are trying to achieve, and how much you know about programming microcontrollers.

   IIRC, assuming you have good quality, bandwidth limited, low-impedance signals, the default set-up for analogRead will give (roughly) 150k samples/second (IIRC). If the signal impedance is low-enough, you can tell the ADC to reduce the sample time (by writing some code, the library doesn't support this), and get about 300k samples/second.

   If you bypass analogRead, and go straight to the ADCs (with your own code), Maple can get about 800k samples/second.

   The Maple has two ADCs, so if you write the code, and use both ADCs, there is a theoretical 1.6M sps available.

   IIRC, no one has been able to write to an SD card fast enough to take that sort of data rate.

   (Try searching this forum for the previous discussions and tests of the ADC performance, I am going from memory).

   (Full disclosure: I am not a member of LeafLabs staff)

   Posted 3 years ago #
8. 

   luver26
   Member

   That's what i was looking for,I also believe that considering the SD slowing effect,i will anyway get the 10KS/s rate i need moreover I'm trying to obtain a 10KS/s analogread with SD writing speed on 8 ch so i'll have like 8 analog reads followed by a SD data writing;what i want to achieve is to do that with a frequency of at least 8kS/s,what you believe?Anyway I understood the maple pogramming is basic the same as arduino(which i know well enough)so this won't be a problem.

   Posted 3 years ago #
9. 

   mbolivar
   LeafLabs

   (by writing some code, the library doesn't support this)

   Yes it does, actually!

   adc.h provides the (badly-named) void adc_set_sample_rate(const adc_dev * dev, adc_smp_rate smp_rate). The second argument, adc_smp_rate, is an enum specifying the number of ADC cycles to spend sampling.

   So, for instance, you could set 1.5 ADC cycle sample time for all channels on all ADC devices with this (though I haven't compiled it; you may need to include adc.h):

   void set_sample_rate(const adc_dev *dev) {
       adc_set_sample_rate(dev, ADC_SMPR_1_5);
   }
   
   void setup() {
       adc_foreach(set_sample_rate);
   }

   You can then use analogRead() like you normally would, and it'll go much faster. As you explained, however, the signal you're sampling must then have a low impedance etc. if you want the results to be accurate.

   Because of the need to hit the datasheet and make calculations about the quality of the signal before using it, I've intentionally left this function in libmaple proper, to try to encourage its callers to Know What They Are Doing.

   Posted 3 years ago #
10. 

    luver26
    Member

    Thanks that really was heplfull ^_^

    Posted 3 years ago #
11. 

    luver26
    Member

    One more annoying question...the arduino wirless shield(SD implemented) along with the SD library works with the maple board too doesn't it?

    Posted 3 years ago #
12. 

    crenn
    Moderator

    You'll need to use the SD library made for the maple, but it should work as far as I know. You can find the SD library here:
    http://code.google.com/p/maple-sdfat/

    Posted 3 years ago #
13. 

    gbulmer
    Moderator

    mbolivar -

    (by writing some code, the library doesn't support this)

    Yes it does, actually!

    Starting at leaflabs.com, what sequence of links did you click on to get to adc_set_sample_rate?

    I can't find it starting at leafabs.com/docs
    'Type "adc_set_sample_rate" into the Search' is not adequate.

    Posted 3 years ago #
14. 

    crenn
    Moderator

    Docs -> libmaple -> APIs -> adc.h -> Functions (in the list)
    After that, scroll down a little and it's listed there.

    Posted 3 years ago #
15. 

    gbulmer
    Moderator

    Docs -> libmaple -> APIs -> adc.h -> Functions (in the list)

    Yup! Dreadful, isn't it?-)

    A good answer would be:
    Docs -> Language -> analogRead() #Discussion
    Docs -> Language -> analogRead() -> ADC Tutorial
    Docs -> Language -> analogRead() -> pinMode() // if the functionality were a pinMode overload :-)
    Docs -> Language -> analogRead() -> ADC Functions
    Docs -> Language -> analogRead() -> Low-level ADC Functions
    etc.

    IMHO only a C/C++ programmer is going to feel looking in a header file is a good place to look for documentation.

    And I don't think this is good once it is found:

    void adc_set_sample_rate(const adc_dev * dev, adc_smp_rate smp_rate)
    Turn the given sample rate into values for ADC_SMPRx.

    Don’t call this during conversion.

    Parameters:
    dev -adc device
    smp_rate -sample rate to set
    See: adc_smp_rate

    ...

    adc_smp_rate enum
    ADC sample times, in ADC clock cycles.

    These control the amount of time spent sampling the input voltage.

    Values:

    ADC_SMPR_1_5 -
    1.5 ADC cycles

    ADC_SMPR_7_5 -
    7.5 ADC cycles

    ADC_SMPR_13_5 -
    13.5 ADC cycles

    ADC_SMPR_28_5 -
    28.5 ADC cycles

    ADC_SMPR_41_5 -
    41.5 ADC cycles

    ADC_SMPR_55_5 -
    55.5 ADC cycles

    ADC_SMPR_71_5 -
    71.5 ADC cycles

    ADC_SMPR_239_5 -
    239.5 ADC cycles

    I don't like the throwaway line "ADC sample times, in ADC clock cycles."
    Not even "ADC sample times, in ADC clock cycles. The ADC clock is set up to be 12MHz on Maple." or "The default for all ADC pins is set to ADC_SMPR_55_5 which is x.y microseconds when the ADC clock is at the default 12MHz."

    Posted 3 years ago #

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