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Topic: Shift Register Issue (Read 856 times) previous topic - next topic

calumk

Hi all, Having an issue with my project involving shift registers.
I have 9 registers all chained together, and the first 7 work perfectly, Outputing whatever i send them with shiftOut, but the last two are not working...

They seem to be constantly outputing on all 8 outputs

If i send out '0' on every register, every output turns off, EXCEPT for all of the outputs on the last two registers...

they just wont turn off!
The data pin also seems to have a voltage (BUT ONLY ON THE LAST TWO + THE DATA OUTPUT ON THE 7th)

Its driving me insane!
Any ideas?

johnwasser

Well, if the data output of the 7th shift register is stuck HIGH that would explain why every shift stage beyond that sees a HIGH.

Swap the 5th and 7th chips.  If the problem follows the chip then the chip is bad.  If the problem stays on the 7th chip there is probably a bad connection near there.
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calumk

oh no :/
Ive soldered the chips on.... i dont think i can swap them? ...

ahh this could get tricky :/

johnwasser

A rookie mistake.  :)

Check the connections of the 7th shift register.  Could be that a solder connection or trace is bad (open) or bridged to another pin.

If you don't see any problems in the traces and or solder joints it's probably time to de-solder.  If you do get that far it might be good to pick up some sockets for whatever chips you remove.
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Grag38

#4
May 04, 2011, 01:42 am Last Edit: May 04, 2011, 01:45 am by Grag38 Reason: 1

oh no :/
Ive soldered the chips on.... i dont think i can swap them? ...

ahh this could get tricky :/



It's better to use solder slots (sorry I'm french) that you solder, and put the chip on it after checking your circuit.
I mean this kind of stuff :



This allows two good things :

-1- you can not dammage the chip by an excessive temperature when you sodler it.
-2- if one chipset is dead it's easy to replace it...

keep it mind

Grumpy_Mike

How much decoupling do you have, I suspect none:-
http://www.thebox.myzen.co.uk/Tutorial/De-coupling.html
Also what physical distance are these appart, logic level signals don't travel well over a few feet.

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