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[on:]

Hi,

I've been using the SD card breakout board supplied by cutedigi....
http://www.cutedigi.com/product_info.php?products_id=4435
It's worked fine on a breadboard, but I'm now trying to make a mega shield with a SD card onboard. The breakout board comes with an SD card holder plus half a dozen extra components, from what I can make out these extra components are only there to provide 3.3 volts to the card. Does anyone know if this is correct? I think I only need to include the card holder on my shield, and there's no need for these extra components, I think can just use the 3.3v supply from the board, again does anyone know if this is correct?

If I am correct on all counts, then why does the breakout board use these extra components, is it designed for for prototyping non-arduino systems, or does it date from a time before arduinos had a 3.3v supply?

Regards

[Reply #1 on:]

ALL interaction with the SD card, data in and data out, is at 3.3V. Just "powering" the holder at 3.3 volts doesn't make sense.

You need to incorporate the entire schematic of the breakout board into your schematic.

[Reply #2 on:]

Thanks Paul,

Either I've misunderstood what's happening, or I haven't explained my issue clearly. The SD breakout boards' Vcc pin takes power from the arduino 5v pin and feeds this to a 3.3v regulator on the breakout board, which then goes straight to pad 4 on the SD card (Vcc 3.3v).

The data/control pins (MISO,SCK,SS and MOSI) go straight from the arduino to the SD card via various resistors to drop the voltage. (I'm not suggesting I can do without these).

What I am saying is do I really need the 3.3 v regulator, capacitors, diodes and resistors from the breakout board when all they do is provide 3.3 volts to pad 4 on the card? Can't I just use the 3.3 volt source on the arduino?

Hope this clarifies the question.

[Reply #3 on:]

Can't I just use the 3.3 volt source on the arduino?

Can't hurt (but one SD card and one breakout board) to try it. Disconnect the 5V wire, and run one from the 3.3V pin on the Arduino directly to the pad.

[Reply #4 on:]

I've just found this on one of Ladyada's pages....

There is a small power supply on the board for generating 3.3V @ 250mA. We don't use the 'built in' 3.3v regulator on the Arduino because its only guaranteed up to 50mA and some SD card need a lot of power when writing. This supply is nice and steady, we can use it as an analog reference too! We have two sets of bypass caps to try and keep both 5V and 3.3V supply nice and clean - the 100uF ones are for the low frequency noise and 0.1 for higher frequency

I guess that explains the reason for not using the 3.3v supply from the motherboard.

[Reply #5 on:]

Thanks Paul,


What I am saying is do I really need the 3.3 v regulator, capacitors, diodes and resistors from the breakout board when all they do is provide 3.3 volts to pad 4 on the card? Can't I just use the 3.3 volt source on the arduino?

Hope this clarifies the question.

The arduino's 3.3v pin can supply a max of 50ma, where as newer SD cards can take nearly 100ma while writing etc, so therefore using arduino's 3.3v pin can lead to instability. So please use your own dedicated 3.3v regulator for the sd card.