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What would be the total GPIO pins available.

finian826

Good day,

I am thinking of employing 1 or 2 Rpi's into my model train layout to remote manage my turnouts and other specialty items on my layout.

I know through GPIO-P1 I have 17 available GPIO pins. From some of my other reading I have discovered on the new model B's there was a P5 added that gives 4 more GPIO pins for usage, but it also says in the same document that those pins are used by the system. The available pins on P5 are GPIO28-GPIO31, but those are used as follows: GPIO28-31 are used by the board ID and are connected to resistors R3 to R10.

 

I know that some are also avabile via S5 which from my understanding will eventually be used for the upcoming camera board.

 

So if I read correctly, theorietically I could have 25 possible GPIO pins available or would it only be 21 if I take and use the 4 from S5.

 

Any input on this from others would be great.

 

Thanks

Terry

  • in reply to finian826

    Terry,

     

    be aware if you want total isolation from the Pi, and if you use for example the SPI interface and the MCP23S17 (SPI) you can put in the middle a digital isolator like the ISO7241 that can support the high speed of the SPI interface and has separate power supplies for each side.

     

    Silicon Labs also has similar products, and as far as I remember you can get samples from both.

     

    -J