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Topic: SD card module only working when connected to multimeter probes? (Read 688 times) previous topic - next topic



I have an Arduino Mega and the SD card module found at this link: http://www.ebay.com.au/itm/SD-Card-Module-Slot-Socket-Reader-Arduino-ARM-MCU-Read-And-Write-/180868021964#vi-content

I am using this test code to check if it is working: http://arduino.cc/en/Tutorial/CardInfo

The problem was that it was not working, so I started checking voltages on the SD card module. Then I found that when I have the multimeter probes on the SCK and GND pins the code works. I unplugged the probes from the multimeter but left the ends attached to the SD card module and it still worked. As soon as I remove one of the probes from the module (either GND or SCK), the code no longer works.

I have no idea what is going on here but is it something to do with the probes changing the resistance of the pins that is making it work?

SurferTim

#1
Oct 17, 2013, 12:27 pm Last Edit: Oct 17, 2013, 01:22 pm by SurferTim Reason: 1
You are not the only person having trouble with that SD card breakout board.
http://forum.arduino.cc//index.php?topic=193520.0

Those boards do not have a logic level converter, so the SD card gets 5v from the Arduino into its 3.3v inputs. Your probes may have just enough capacitance to keep the clock (SCK) from reaching 5v.

I know the site says it is 5v compatible, but I don't see how. SD cards are 3.3v devices.

edit: Do not be fooled by those resistors (R1 to R4) on that board. Those are not voltage dividers to lower the input voltage. They are weak pullups connected to the 3.3v power bus. I attached the schematic to this post.

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