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Faint LED's while using an Arduino Micro and shift register? Answered

This is more of a "How things work" question, but a question non the less.

I have five 595 shift registers hooked up to an arduino micro. Everything is wired correctly, and it all works beautifully on my test bed, all the codes work fine. Only issue is that my LED's are only about half as bright as the sun..

Anyways, I was testing one of my codes at work, and due to the bright, flashing LED's that were popping up on the 595 portion of the board, decided to just power them off but removing the 5v leg going to them (I know, it would have been better to just set in an "all off" in the code, but I figured removing the power pin would work). However, removing the 5v leg to the 595 didn't turn them off: it only made them about a third as bright as they normally are. I checked to ensure that there was no power getting to the 595's, and there is not. 

So: why would the LED's connected to the [unpowered] 595's still turn on?

4 Replies

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steveastroukBest Answer (author)2014-08-20

They're loading the datalines.

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DoctorWoo (author)steveastrouk2014-08-20

Oh yeah...so their [595's] are just picking up some power off the datalines as well?

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user
steveastrouk (author)DoctorWoo2014-08-20

Yes. There's an internal leakage (probably) when the 595s +ve supply is floating.

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