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Can a BBB run one or two strings simply via the GPIO?

Started by learnedinuk, December 16, 2018, 01:52:36 PM

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learnedinuk

All,


I have a BBB laying around and wondered if I could use it to drive 2 small strings via FPP in my house for lights down a railing. I know I can with a Raspberry Pi and have done so. I am wondering if i can do the same thing with a BBB?


My research has been fruitless so far.


Any thoughts?

JonB256

While I know that a BBB with the proper Cape can drive 4, 8 or 16 outputs for pixels, I don't recall anyone ever doing it from just the GPIO outputs.

Dan Kulp would definitely know. If he doesn't see this and answer soon, send him a Private Message.
Long time Falcon, FPP and xLights user

learnedinuk

Thanks. Can you point me to the proper cape? Or a thread about making one?

dkulp

Technically you could run them directly from the GPIO, but just like on the Pi, it's strongly not recommended due to the 3.3v vs 5v difference and the potential to damage the GPIO's one the BBB.   A simple buffer chip and 100ohm resistor is all you "need". 


I believe that I do have some F8-B capes available if you are interested.   They have 8 outputs, fully fused and buffered, along with a bunch of expansion capabilities like DMX and differential outputs and such, but you likely don't need those.
Daniel Kulp - https://kulplights.com

pixelpuppy

-Mark

yo3ham

hello all,

I have a BB Green Wireless and the FPP docs says it doesn't support the capes because some GPIO conflicts. Still I believe there are ***SOME*** ports not conflicting (I don't need 48 channels... a few will do !!!) and, same as Learnedinuk, I want to connect a few WS281x strings to the BBG. I can manage to do buffering & stuff so that I don't "fry" the GPIO pins.
However I don't know what the pins are for each WS281x channel on the BBGW headers.

Is there some documentation somewhere about this?

dkulp

The pins that cannot be used on the BBGW:

P8 Header:  11, 12, 14, 15, 16, 17,18, 26
P9 Header:  12, 28, 29, 30, 31
Daniel Kulp - https://kulplights.com

yo3ham

Perfect! thank you for this, and also for the JSON link about conflicting pins on BBGW - extremely useful !

IMHO since this is in large part a DIY community, I believe that a short documentation about the pins on the BBB variants, that can be used with WS281x, somewhat similar to what exists for the RPi, would be very useful. 
I could not find anything in the FPP documentation or wiki - beyond the use of a ready-made cape. This question will come back time and again... and probably more since the simple/cheap capes on Kulp Lights seem to be out of stock.

yo3ham

Hello again, I have a BBG Wireless laying around (not purchased specially for FPP), I use wired ethernet connection using a USB-Ethernet dongle for connectivity.
So, if I don't use/disable the internal wireless Wi-Fi, can I use the pins specified in the previous posts?

The problem is that most of the cape configurations use these pins.

CaptainMurdoch

I'll have to let Dan respond on whether those pins are usable if you disable the onboard WiFi, but I did want to comment on your prior comment about finding out about the pins.

In FPP v6, you will be able to mouseover the port number for each port in the Pixel Strings config UI and a tooltip will be shown which will show you what pin the output is using.

For the WiFi pins, you can always try it with a pixel while waiting for an answer.  It won't mess up the pixel, it will either work or it won't.  The voltage or signal coming out the pin while in WiFi mode isn't going to fry the pixel.
-
Chris

yo3ham

Thank you Captain :-)  However I remember reading that trying to use a conflicting pin with WiFi enabled will seriously lock up the board, needing a hard reset. I don't remember where I read this, however. It is clear that the Wifi code is kernel space so anything interfering with it can spell trouble.

CaptainMurdoch

I will defer to Dan then based on his BBGW knowledge, but you could also research disabling onboard WiFi by removing a DTB.  You could also make your own FPP virtual EEPROM with a strings config file that didn't use the conflicting pins.
-
Chris


dkulp

On the beagles, it would be editing /boot/uEnv.txt to uncomment  the line "#disable_uboot_overlay_wireless=1".    That should disable the onboard wifi.  At least it does for the BBBW.  Not sure on the BBGW. 
Daniel Kulp - https://kulplights.com

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