Relay shield power pins

Hey guys,

I apologize if this is too vague, I am pretty new to electronics so I’m not really sure what information is relevant. Anyways, I am using the relay shield with my Photon and have it powered with a 12V power supply which works fine. However I am trying to hook up a couple of shift registers running on 3v3 logic and so I tried using the 3v3 pin as a power output. I hooked up a GND pin on the photon to the ground pin on the registers as well. When I hook those up the photon doesn’t power on even though I see that the relay shield has power through the blue LED. I am wondering if maybe the photon is powered through that 3v3 pin when using the relay shield? I am confused as to why it won’t power on when I connect those pins, any help would be greatly appreciated.


Maybe you can post a pic of your setup and some schematics.

You shoule be able to power the shift register off the 3v3 pin.
The issue you are describing would somehow sound as if you’re pulling the RST pin LOW somehow.

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I am at work but I had a little bit of time to throw this together. I am tying reset to power and /OE to ground

I am following the bldr tutorial for this spark fun shift register breakout just fyi:

I can get some more info if you need it later tonight. Thanks for your help!

How about removing all the connections and then only add back one by one with the Photon powered?
Starting with only one shift register and GND, then 3v3, …

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Im sorry I haven’t had time to look at this, but thanks for your suggestion I am sure I will figure it out. Just wanted to see if I missed something obvious.