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Ether Mega Digital Pin 4

Posted: Mon Aug 08, 2016 3:08 pm
by andydenniscoates
Hello,

I've just received my Ether mega and its excellent.

On Digital Pin 4 seems to be pulled down by default on the board tracking, does anyone know where i can remove a resistor or cut a track to enable it to be Pullup by default.
I had to do this on the ethernet shield when using the Arduino/ethernet shield combination which worked but i cant find the track on the EtherMega.

Any suggestions?

Thanks

Andy

Re: Ether Mega Digital Pin 4

Posted: Wed Aug 10, 2016 3:06 pm
by skiphod
D4 is used as the Chip Select signal for the microSD card reader/writer. If you are determined to use it for a pullup input it would probably be wise to make sure no card is in the card holder. Then just do (in the setup function):

pinMode(4,INPUT_PULLUP);
and don't do SD.begin(4); or that will put it back into OUTPUT mode.


if you just want it to sit high forever then:
pinMode(4,OUTPUT);
digitalWrite(4,HIGH);

Re: Ether Mega Digital Pin 4

Posted: Wed Aug 10, 2016 11:04 pm
by skiphod
If you want to physically remove the pull down resistor arrays from the board (which will wreck the SD feature) the array is RN6 on the schematic and is located immediately below the main ICSP header stack. It is a 1K array labelled "102". Caution: there is another "102" nearby; make sure you remove the one closest to the ICSP header. I would use an SMD rework gun for this, some fresh flux and some solder wick. This will remove all data signals from the SD socket except MISO and if there is no card in the socket that will not connect to anything. That will prevent the data signals from an SD card interfering with the SPI bus which is needed for the W5100 ethernet chip.