Go Down

Topic: Is there a SD Tutorial? (Read 1 time) previous topic - next topic

lax123

Jun 29, 2012, 03:38 pm Last Edit: Jun 29, 2012, 03:57 pm by lax123 Reason: 1
Hi,
is there something like a complete tutorial for an SD Module like this:
http://www.ebay.de/itm/180868021964?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1439.l2649

If i need external power supply and all the other things?


I saw a tutorial where the author would use a digi IO pin to power up the SD module. But then i read somewhere writing to sd might use 100mA, isnt that way above the max specs?
I dont want to use a faulty tutorial ending up burning my ardu :-(

is using external 9V power via jack and ardu attached to usb at the same time ok?

johnwasser

http://arduino.cc/en/Reference/SD/
http://arduino.cc/en/Reference/SDCardNotes

You don't need external power.  Looks like it has a built-in 3.3V regulator so you can power it from the +5V pin which can supply about 400 mA.

It's not clear if they support both 3.3V and 5V logic.  Doesn't look like enough resistors to do that and they don't provide a schematic.  The Arduino inputs will work with 3.3V logic and the SD-card inputs will probably work if you put a voltage divider on each.  Two 1k resistors in series between the Arduino output pin and Ground.  The signal between the two resistors (2.5V) should be safe for the SD-card inputs.
Send Bitcoin tips to: 1L3CTDoTgrXNA5WyF77uWqt4gUdye9mezN
Send Litecoin tips to : LVtpaq6JgJAZwvnVq3ftVeHafWkcpmuR1e

lax123

#2
Jun 30, 2012, 01:32 pm Last Edit: Jun 30, 2012, 04:42 pm by lax123 Reason: 1
thx for the reply,

i found a schematic. Do i still need those extra resistors for a voltage divider, can u see that?

If i wouldnt use a divider if needed, what would happen? Destroying the SD card?

You say "supply about 400mA", would that not overload usb? i think i read somewhere it would shut down at 300mA by fuse in the ardu.

johnwasser

The USB fuse in the Arduino is 500mA.  The Arduino itself uses less than 100 mA leaving 400 mA for various peripherals.

I don't know if SD card inputs are supposed to be 5V-tolearant or not.  If not, using a 5V signal on them might well destroy them.  Most shields with SD sockets provide some sort of level shifter.

You could power your Arduino on 3.3V but then you would have the problem of 16 MHz be out-of-spec for 3.3V power. :(

Send Bitcoin tips to: 1L3CTDoTgrXNA5WyF77uWqt4gUdye9mezN
Send Litecoin tips to : LVtpaq6JgJAZwvnVq3ftVeHafWkcpmuR1e

lax123

thx,
so you would strongly advise me to use the divider?
i only have 1k resistors, would that be sufficient? i also have somewhere 100k i think, that would be better, right?

Im just wondering why there r like 30 sellers on ebay for exactly this sd module without anyone mentioning that u d need some external things like resistors to make it properly work. so i guess like 90% would just connect it to ardu like every other sd module with lvl shifters...

Go Up