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[on:]

At use SD card in devices with a battary power, the great value has consumption of energy by the card which can make 40-80 ma.
For reduction of consumption of energy by a SD card it is necessary to switch it in IDLE state when it is not used.
For this purpose to add to SD library a method making deinitialization cards and SPI:

in file Sd2Card.h to add the bolded:


/**
 * \class Sd2Card
 * \brief Raw access to SD and SDHC flash memory cards.
 */
class Sd2Card {
 public:
  /** Construct an instance of Sd2Card. */
  Sd2Card(void) : errorCode_(0), inBlock_(0), partialBlockRead_(0), type_(0) {}
  uint32_t cardSize(void);
  uint8_t erase(uint32_t firstBlock, uint32_t lastBlock);
  uint8_t eraseSingleBlockEnable(void);
  /**
   * \return error code for last error. See Sd2Card.h for a list of error codes.
   */
  uint8_t errorCode(void) const {return errorCode_;}
  /** \return error data for last error. */
  uint8_t errorData(void) const {return status_;}
  /**
   * Initialize an SD flash memory card with default clock rate and chip
   * select pin.  See sd2Card::init(uint8_t sckRateID, uint8_t chipSelectPin).
   */
  uint8_t init(void) {
    return init(SPI_FULL_SPEED, SD_CHIP_SELECT_PIN);
  }
  /**
   * Initialize an SD flash memory card with the selected SPI clock rate
   * and the default SD chip select pin.
   * See sd2Card::init(uint8_t sckRateID, uint8_t chipSelectPin).
   */
  uint8_t init(uint8_t sckRateID) {
    return init(sckRateID, SD_CHIP_SELECT_PIN);
  }
  uint8_t init(uint8_t sckRateID, uint8_t chipSelectPin);

  /*
   * deinitialization SD flash memory and stop SPI
   */
  void stop();




In file Sd2Card.cpp:


void Sd2Card::stop()
{
     // command to go idle in SPI mode
     status_ = cardCommand(CMD0, 0);
#ifndef SOFTWARE_SPI
     SPCR &= ~_BV(SPE);
#endif
}





And also to add this method in a wrapper. In file SD.h:


class SDClass {

private:
  // These are required for initialisation and use of sdfatlib
  Sd2Card card;
  SdVolume volume;
  SdFile root;
 
public:
  // This needs to be called to set up the connection to the SD card
  // before other methods are used.
  boolean begin(uint8_t csPin = SD_CHIP_SELECT_PIN);

  void stop();




In file SD.spp:

void SDClass::stop()
{
   card.stop();
}


Now when the card isn't necessary it is possible to cause this method. See example:

Code:

  // see if the card is present and can be initialized:
  if (!SD.begin(chipSelect)) {
    Serial.println("Card failed, or not present");
    // don't do anything more:
    SD.stop();
    return;
  }

  // Using SD card....
 
  // deinitialize SD card
  SD.stop();
 

The card in IDLE-stae will consume considerably smaller current that will lead to the big economy of energy of the battery.


P.S.
Excuse for my bad English

Best regards,
Alexander (Azimutx)

[Reply #1 on:]

makes sense for some apps, have you checked the author of the library? or - http://code.google.com/p/beta-lib/issues/list

[Reply #2 on:]

Thanks Azimutx for this. The major hurdle for the data logger that i am working on was the sd card power consumption. I was initially going to use an opticoupler on the cards ground. This saves me the effort, and the pin.

[Reply #3 on:]

What type card are you using?

Modern cards draw less than 1 ma when initialized and idle.  I tested a Transcend 8 GB class 6 card and it draws less than 1 ma before and after it is initialized.  It draws over 30 ma during read access and more than 40 ma for writes.

An older SanDisk 1 GB card, manufactured in 2006, draws 1 ma before initialization and 8 ma when initialized.  I think this card was designed long before 2006.