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Topic: Questions on making a minimal/custom Arduino circuit @ 3.3v/8Mhz? (Read 14415 times) previous topic - next topic


I am stumped.
Send a pm to fat16lib, ask him to review this thread.
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.


well I PM'd him.. and got a response..

although Im not sure it really applies to me? or if Im over thinking it..etc.etc..

but basically fat16lib responded that SD cards will work with +3.3v/8MHz boards...

he stated he uses one with the Pro-Mini..

and also said he uses this breakout board: https://www.sparkfun.com/products/544

which to me looks like a 'bare' bones SD socket on a pcb.. (which is good.. since I too have nothing on my SD card)

however.. it looks as if the Pro-Mini 'does' in fact use an external 8Mhz crystal on-board?

and I am using 8MHz INTERNAL clock??..

could this be where the problem lies?

I have changed out the MOSI/MISO/CS/CLK wires too just in case they were 'bad'... still same results..

I wanna hear from ANYBODY that has done this on an internal 8MHz clocked chip?

this is starting to kill my self-esteem!  hahaha  ;)

thanks guys!


I'm sure that what you are trying to do is possible. It should not matter whether you use a 8MHz crystal or 8MHz internal clock, the SD card does not have an internal time reference so it doesn't care what the exact clock speed is. I suggest:

1. With the SD card removed, run some sketches on your board to test it out. Include sketches that toggle the pins that you use to communicate with the SD card.

2. Check your connections between the mcu and the SD socket carefully, looking for open/short circuits.
Formal verification of safety-critical software, software development, and electronic design and prototyping. See http://www.eschertech.com. Please do not ask for unpaid help via PM, use the forum.



Im baffled still then...

If the SD card doesnt matter about the clock (external/internal)..

then why isnt it possible?  (curious)..

fat16lib says he does it with pro-mini.. +3.3v & external 8Mhz crystal...  (stand alone SD socket..no caps/resistors..etc)

so to comment back it 'should' be possible..if others have done it? 

I have an LED on pin 13..and that works fine..  I can go through and check the other pins too (12, 11, 10).. to ensure they 'toggle'..(they should..its a brand new chip from the factory)

as far as connections..  its on a breadboard.. and I have replaced the jumpers wires once to check to see if bad connection


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