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I have RPI's GPIO connected to a relay board, everything works fine, and relays are nicely controlled, but there is one problem: when the RPI restarts, the GPIO pins have unstable state and keeps changing very quickly, which in turns causes the relays connected to them to flicker very quickly, which can destroy the devices connected to them.

P.S. I'm talking about GPIO 14

What is going on here, and how to stop that?

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  • The GPIOs do not have an unstable state. Which GPIO are you using? Please add that detail to your question.
    – joan
    Dec 7 '15 at 12:08
  • GPIO 14, and this only happens on start/restart. A note added in the question
    – securecurve
    Dec 7 '15 at 12:21
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GPIO 14 (pin 8 on the expansion header) is the UART TXD. It will be active during boot as boot messages are sent on the serial link. After boot the UART may also be used to login to the Pi.

You can disable most (but not all) of the boot messages with the raspi-config tool of Raspbian. The same tool will also disable the use of the UART for a login console.

I suggest you use a different GPIO.

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  • Thanks joan, will check it and confirm throughout the day!
    – securecurve
    Dec 7 '15 at 12:36
  • I confirm your answer is correct.
    – securecurve
    Dec 7 '15 at 14:03

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