Default state GPIO

Shawn RansfordShawn Ransford New Member Posts: 20
Hello all,
I am using the UP board to control a series of relays. A number of the GPIO default as HIGH output at boot in advance of my program configuring. This is no good for my pumps as they come on for a few seconds at boot. This seems to be a common issue amongst SBCs. However, I am hoping we have a solution here on the UP side. I already have one client complaining. In the Wiki, it seems to allude to this as a known issue...

"There are some limitations and considerations which the user should be aware of:
The level-shifters are configured as outputs by default at power-on, and may be driving a high output signal (3.3V). This may have implications for users who are connecting external electronics such as motor drivers. This will be addressed in the final production version of the UP board.

I assume we are past final production? Do we have a fix? I have started poking at some of the kernel code to see if there might be a file where I could modify the defaults...or maybe use a pullup. Any and all help would be greatly appreciated!


  • WereCatfWereCatf New Member Posts: 201
    If you're willing to use two GPIO-pins instead of one to drive the relay, you could use an XOR-gate to ensure the pin is always LOW at boot.
  • Shawn RansfordShawn Ransford New Member Posts: 20
    I am using a set of RPi compat relays that are hard wired to specific GPIO on the header...hands are tied :(
  • WereCatfWereCatf New Member Posts: 201
    Well, if you're not willing to/are not skilled enough to modify them, then I unfortunately don't have any better advice to offer you :( A lot of people have had the exact same issue as you and I always recommend an XOR-gate because it's a very simple and effective fix.
  • Shawn RansfordShawn Ransford New Member Posts: 20
    Fix? Eh...let's call that a rig. I do appreciate the feedback though. The hardware I am using is "hardwired" in the PCB. Unless, I am missing a mod on the software side, my only option would be to go back to PCB design and add the XOR. Fun.
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