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Topic: how to add an sd card socket? (Read 203 times) previous topic - next topic

sparten9999

im trying to figure out how to add a full size sd card socket to an uno. all i seem to find is how to use the preassembled breakout boards.

im pretty sure i need a logic voltage converter but i dont know which one i should use or how to connect it.

thank you

PaulS

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all i seem to find is how to use the preassembled breakout boards.
So, what is the problem with using one of them?

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im pretty sure i need a logic voltage converter but i dont know which one i should use
One that takes the appropriate input voltage and converts it to the appropriate output voltage.

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or how to connect it.
Correctly, of course.

The pre-assembled boards have already figured this out. Study their designs.
The art of getting good answers lies in asking good questions.

CrossRoads

I like using 3 gates of CD74HC4050 powered by 3.3V for the 5V to 3.3V conversion of CS, MOSI, SCK.
Then 1 gate of 74HC125 powered by5 5V for the 3.3V to 5V conversion of MISO. Control the OE pin with the unbuffered CS signal. That keeps 5V off SD's MISO pin so the pin is not dragging down the line, and if the card is slow to release MISO the buffer ensures MISO is off when the card is not selected.
No messing with resistors for voltage dividers on potentially high speed signals, the fast cards don't like that.
Then you have a couple spare gates for other uses, and SCK and MOS are at 3.3V levels for other devices as well that need it.

Most cards need a 3.3V regulator as well, the 150mA from the Arduino Uno regulators is not enough. I use a 400mA regulator myself:
http://crossroadsfencing.com/BobuinoRev17/
You can see it above the SD socket on this '1284P board I offer:
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.

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