microsd card detect - 5V?

Discussion in 'General Electronics Chat' started by ToBeFrank, Jan 14, 2011.

  1. ToBeFrank

    Thread Starter New Member

    Nov 18, 2010
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    Is it safe to connect the card detect switch of a microsd connector to a 5V pullup? If it's just a switch that isn't electrically connected to the microsd card (the card simply connects it), I think this is ok, but I wanted to verify.
     
  2. marshallf3

    Well-Known Member

    Jul 26, 2010
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  3. ToBeFrank

    Thread Starter New Member

    Nov 18, 2010
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    I know that, but as I said, I'm wondering if the card detect is simply a switch that gets connected when the card gets inserted. If it is, and it's not electrically connected to the microsd, I'm safe using a 5V pullup. That means I don't have to do a level translation from 3.3V to 5V.
     
  4. tom66

    Senior Member

    May 9, 2009
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    Are you already using 5V directly with your microSD card?

    Also, most 5V ICs will accept anything >2V as logic high. Check the datasheet for minimum inputs; stay clear of them, and you should be fine with 3.3V.
     
  5. ToBeFrank

    Thread Starter New Member

    Nov 18, 2010
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    No, I have a voltage regulator to provide 3.3V from the 5V supply, and the circuit is set up to properly interface the 3.3V and 5V devices.

    This is why I want to use a 5V pullup. The micro I'm using has a minimum logic high of 3.25V, which means I have to use a mosfet to translate the 3.3V to 5V on all outputs of the microsd. If I can use a 5V pullup for the card detect line, I can avoid one mosfet and the associated resistors.
     
  6. marshallf3

    Well-Known Member

    Jul 26, 2010
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    3 ea. 1N914 or 1N4148 diodes (0.01 ea) in series with a 5V line will pull it down to 3.2V
     
  7. SgtWookie

    Expert

    Jul 17, 2007
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    That's if there is current flow through the 1N914/1N4148 diodes. 0.5mA would be about right, a 6.2k resistor to ground would give just a bit more than that.
     
  8. marshallf3

    Well-Known Member

    Jul 26, 2010
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    You're right, the diodes won't drop voltage unless a tiny bit is going through them.
    A 4.7K might be easier for him to find and work just as well.

    Everyone should have at least 100 of these on their shelf:
    1N4148 (or 914) @ 0.01 ea
    10K 1/4W 1% @ 0.02 ea
    4.7K 1/4W 1% @ 0.02 ea
    2N3904, 2N3906, etc stuff that's dirt cheap.
     
  9. blueroomelectronics

    AAC Fanatic!

    Jul 22, 2007
    1,758
    98
    The card detect is just a simple switch on the socket. 5V is fine with a simple pullup.
     
    panfilero likes this.
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