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Topic: Hooking up an SD card- 3.3v needed? (Read 6303 times) previous topic - next topic

bigred1212

Sep 03, 2013, 06:32 pm Last Edit: Sep 03, 2013, 06:35 pm by bigred1212 Reason: 1
I'm looking for a little guidance on how to hook something like this up:

Deal Extreme SD Card Slot Reading Writing Modules - Blue + Silver (2 PCS), SKU: 205308 Price: US$4.80
http://dx.com/p/micro-sd-tf-card-slot-reading-writing-modules-blue-silver-2-pcs-205308

On those modules I see











Board Pin
gnd
3.3v
5v
sdcs
mosi
sck
miso
gnd


I am assuming that to use the SD Library (http://arduino.cc/en/Reference/SD) I do this:











Board Pin   Arduino Pin
gnd  
3.3v  
5v   5v
sdcs   =ss, cs; Pin 10
mosi   =do; Pin 12
sck   =clk; Pin 13
miso   =di; Pin 11
gnd   gnd


I don't know what to do with the first ground pin or the 3.3v pin.  Do I need them?

If I do, can I create a voltage divider from 5v with a 100ohm and a 200ohm resistor and shoot that in, or is this not just power and somehow needs to be variable?

Any help appreciated.

EDIT:  Should have noted- running an Uno.

pylon

Quote
Board Pin        Arduino Pin
gnd        
3.3v        
5v        5v
sdcs        =ss, cs; Pin 10
mosi        =do; Pin 12
sck        =clk; Pin 13
miso        =di; Pin 11
gnd        gnd


MISO is pin 12 on the Arduino and MOSI is pin 11, the rest probably works. From the pictures my guess would be that the board contains a voltage regulator to get the 3V3 from the 5V but that's just a guess, the shop doesn't provide the necessary information (I personally never buy from such shops).

CrossRoads

Looks like it uses resistor voltage divider for the signals. Faster cards will have issues with that.

But on the bright side,
"the back of the card board reserves the weld Micro SD Card, the user can add their own welding Micro SD Card."
break out those welding masks ;)
Designing & building electrical circuits for over 25 years.  Screw Shield for Mega/Due/Uno,  Bobuino with ATMega1284P, & other '328P & '1284P creations & offerings at  my website.

bigred1212

#3
Sep 03, 2013, 11:44 pm Last Edit: Sep 04, 2013, 12:38 am by bigred1212 Reason: 1
Looks like I flipped MISO and MOSI. Thanks.

Quote

From the pictures my guess would be that the board contains a voltage regulator to get the 3V3 from the 5V but that's just a guess,


Do you think I need to feed it 3.3v or will it maybe work unconnected?  How do these generally work?

Quote
Looks like it uses resistor voltage divider for the signals


No idea what is meant by this.  Signals where on what? The 3.3v pin?  Miso?  Mosi?

You don't weld your electronics together?  Much better than super glue...

EDIT:  Didn't realize there was a whole "storage" group for some reason.  This got moved. Looks like half the questions here are like mine.  Now reading a bunch of threads trying to answer my own questions.

EDIT:  Found this
http://dx.com/p/doubleside-sd-card-write-reader-storage-module-white-silver-173832
http://www.elecfreaks.com/store/sdmmc-card-module-double-side-p-448.html

Same card- two places. It looks like it works on just 5v which makes me think I could ignore a 3.3 pin on one of these others.  Check that, looks like it will work on 5v but steps in down to 3.3 internally.  Very confused now.

CrossRoads

I don't know what's confusing.
The board is basically this.
Three 5V signals come in and go thru voltage dividers to change to 0/3.3V level.
One signal comes out at 0/3.3V levels which can be read as  high/low by a 5V arduino.
(0.6 x Vcc is the minimum high; 3V with a 5V supply)
There is an onboard regulator to make 3.3V current. The 3.3V current supplied by a typical Arduino is insufficient to power an SD card.

However, the resistor dividers degrade the signal; enough that running some cards at high SPI speeds have had issues reported.
Designing & building electrical circuits for over 25 years.  Screw Shield for Mega/Due/Uno,  Bobuino with ATMega1284P, & other '328P & '1284P creations & offerings at  my website.

bigred1212

Were you able to find a datasheet on that module?  There are onboard regulators and voltage dividers on that module?  If it doesn't need the 3.3v pin, do you have a guess as to why is it there?

CrossRoads

I did not see any datasheet.
There is an onboard regulator, you can clearly see it in the SOT223 package.
There are voltage dividers, you can easily see the little 0603 size resistors.
There's also some caps, likely on the input & output. And a diode.
3.3V output pin - provides the option to power from 3.3V directly?  Test pin for manufacturing?

This one looks better
http://dx.com/p/freaduino-sd-sdhc-micro-sd-tf-card-shield-expansion-board-white-silver-168964
Appears to have transistors to level translate the control lines.
This one too
http://dx.com/p/stackable-sd-tf-card-expansion-board-blue-black-214247
Designing & building electrical circuits for over 25 years.  Screw Shield for Mega/Due/Uno,  Bobuino with ATMega1284P, & other '328P & '1284P creations & offerings at  my website.

deleenheir

I ordered a cheap version with resistors from DX => corrupted my cards each time
Made my own with a voltage divider => works on low speed

Now i ordered one with transistors:
http://dx.com/p/v76-multi-functional-sd-micro-sd-tf-card-dual-side-reading-writing-module-blue-silver-221200
Since i didn't want a stackable shield (it's going in a stand alone project) + it's cheaper...


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