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F8-B Cap and GPIO Pins

Started by asualum2001, June 16, 2020, 04:14:01 PM

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I am considering purchasing a F8-B cap.  One thing that I would like to be able to do though is have access to the GPIO pins to set some inputs.  Is it possible to use the 40-pin expansion header to gain access to some of the BBB pins?  If so, is there any kind of diagram that shows which pin maps to which?  I know that it is intended to be used with an expansion board, but I am hoping I can use it for a different purpose.  I currently use a PiCap (w/ Pi3 board) and slipped an expansion board in-between them.  It got me by for my immediate need last year, but hoping to find a cleaner solution.  Since I was considering this board for other reasons, I'm hoping it can meet a couple of needs.


If you just need them as GPIO pins, yea.. there would be 16 available on the header.   Each "version" of the F8-B has slightly different pinout so you would likely need to look at the pinout extracted from the eeprom, but that's relatively easy.

The big "issue" might be around what you are trying to do.   The 40pin header only has 5V and GND.  However, if you try to pull one of the GPI's to 5, you will fry the pin as they are only 3.3V tolerant.  That would be the main thing to be aware of.  In general, you can use the internal pull up resistors to pull to 3.3V and then use a push button or similar to drop to ground on press.   That works quite well.
Daniel Kulp -


I am looking to do something similar. I have a BBB + Kulp K8-B v4.2 cape & running FPP 5.5.  I plan to use physical push buttons to trigger events and change sequences but not sure which pins i can connected the triggers to. Do I connect to the expansion header pins or connect to a string port's "data" connection?

On the cape, I'm only running 2 strands of 2811 lights on string ports 7 & 8.

Can I connect the trigger buttons to the "data" connection on string ports 1-6 or will this blow up the cape/BBB?

If I need to connect to the pins on the expansion header, how would I extract the pinout from the eeprom as mentioned in the post above?

I've also looked here to find the available pinouts but not sure which version of the json applies to my cape. Is it "F8-B-20-v2" or " F8-B-20" ?

Sorry for the 20 questions. I failed to find clarity via the search function.

Thank you in advance

Kensington Graves

I believe Dan posted information on what pins are used on BBB in the "changes coming in FPP v6" thread a few days ago.  It's probably a couple pages back.


I'm planning on buying a new BBB + Kulp K8-B to power my show (250 pixels planned this year, maybe 400 more next year).

I absolutely want to have a trigger button to launch the show as I am not planing on using an FM transmitter: my target audience are pedestrians.

Has anyone figured out which GPIO pins are free to use? I'm planning on using this as an example. 


I'm  going to reply  to myself: seems like GPIOs below 20 are a safe bet. I'm going to check on BBB's doc to confirm if they aren't used for something else.


Quote from: pierlux on August 05, 2022, 04:41:12 PMI'm  going to reply  to myself: seems like GPIOs below 20 are a safe bet. I'm going to check on BBB's doc to confirm if they aren't used for something else.

I was just about to point in the direction of those json files to get a list of what is in use. :)  I have another change idea I want to run by Dan to see if we can make it so that the only GPIO pins that show up on the GPIO input page are the ones that are available (or possibly just disable ones that aren't available, not sure yet).


Thanks!  I think I also talked myself into a K16A-B... since it has nice GPIO pins exposed, so much less work to connect! ;) 


The K8-B also has 4 GPIO pins exposed.   
Daniel Kulp -


Quote from: dkulp on August 13, 2022, 11:47:45 AMThe K8-B also has 4 GPIO pins exposed. 
Are theses the ones marked ttyS1 and ttyS2?


Quote from: pierlux on August 25, 2022, 07:52:22 PM
Quote from: dkulp on August 13, 2022, 11:47:45 AMThe K8-B also has 4 GPIO pins exposed. 
Are theses the ones marked ttyS1 and ttyS2?
Replying to myself: no. It's now obvious to me that I was confusing things. 

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