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Improvements from the prototype

A project log for Orthrus

SD card secure RAID USB storage

nick-sayerNick Sayer 04/17/2017 at 18:360 Comments

I'm making some improvements from the prototype given some of the lessons learned so far.

  1. I'm going to add an AP2331 current limiter to the 3.3 volt LDO output for the cards, just to insure that the host is protected from any transients that may happen when the cards are inserted and/or removed. To that same end...
  2. I'm going to add a power on/off control from the controller to allow it to power up and down the cards. This is simple - all it takes is running a GPIO line to the enable pin on the LDO. The controller will keep the power off on both cards until both are inserted, and it will turn the power off when one is removed. This makes for much easier recovery if something gets wedged.
  3. I'm going to replace the diode+pull-up shifters on the MISO and SCK lines with a buffer chip. This will make the transitions faster, which may be important for high speed stability. The card select lines will stay as they are. The pull-ups on the CS lines will be 1 kΩ instead of 10 kΩ to keep them reasonably fast, but that's probably less critical.

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