TennisMaster08
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Shift register showing all 1's / not working

Thu Oct 14, 2021 4:04 pm

I plan on building a LED Matrix so I've bought a SN74HC595N shift register, and if I onky wire up Vcc to 4.5V and GND to GND of the 4.5V battrry, and output enable(active low) to GND and hook output Qa to Qh via a 10K resistor to ground it gives my all 1's on the output even if i take a new Shift register. And if I hook up SER, SRCLK and RCKL it doesn't display the inputted things, instead the outputs are all high. How can I fix it, and has anyone other ever had the same problem?

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rpdom
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Re: Shift register showing all 1's / not working

Thu Oct 14, 2021 4:09 pm

Can you post a diagram of how you have connected it to your raspberry Pi?
Unreadable squiggle

TennisMaster08
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Re: Shift register showing all 1's / not working

Thu Oct 14, 2021 6:33 pm

I haven't connected it to a Pi yet
Just on a breadboard

ghp
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Re: Shift register showing all 1's / not working

Thu Oct 14, 2021 7:33 pm

As rpdom has already asked: sketches, circuit diagrams, wiring diagrams are the basis on which one can discuss. Textual descriptions are usually not accurate enough.
Have you already connected the shift register to the RPi?

LTolledo
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Re: Shift register showing all 1's / not working

Thu Oct 14, 2021 9:02 pm

show us what you actually have, how you actually hooked everything up


otherwise..... its a bluff...
"Don't come to me with 'issues' for I don't know how to deal with those
Come to me with 'problems' and I'll help you find solutions"

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TennisMaster08
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Re: Shift register showing all 1's / not working

Fri Oct 15, 2021 6:42 am

Here's the diagram, sorry I'm NOT good at drawing diagrams. I tried also hooking it up to a pico instead of the LED's and I got the same results.
I've bought 5 registers and all of them have the same Problem.
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Bildschirmfoto 2021-10-15 um 08.32.41.png
Diagramm
Bildschirmfoto 2021-10-15 um 08.32.41.png (186.53 KiB) Viewed 369 times

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joan
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Re: Shift register showing all 1's / not working

Fri Oct 15, 2021 7:46 am

We need to know how it is connected to the Pi. I suggest you set up one or two and then show clear photos of the connections. We know the datasheet. We need to be able to clearly see which wires go from pin to pin.

gordon77
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Re: Shift register showing all 1's / not working

Fri Oct 15, 2021 8:09 am

isn't SRCLR low to clear it ? So you are permanently clearing it ?
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LTolledo
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Re: Shift register showing all 1's / not working

Fri Oct 15, 2021 10:18 am

the OP should better refer to/use the diagram below:
74HC595_leds.jpg
74HC595_leds.jpg (52.62 KiB) Viewed 324 times

added for "completeness" (note: 3.3v is used as VCC in this diagram)
Raspberry Pi with Shift Register and LEDs.jpg
Raspberry Pi with Shift Register and LEDs.jpg (225.09 KiB) Viewed 319 times
"Don't come to me with 'issues' for I don't know how to deal with those
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mahjongg
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Re: Shift register showing all 1's / not working

Fri Oct 15, 2021 11:28 am

Note that using a button on a clock input will not work reliably, as mechanical switches and buttons have contact bounce, so pressing the button will generate more than one clock pulse. Also you need to add pullup/pulldown resistors on those inputs.

as for the diagram above, If I read it right pin 13 (OE) is NOT connected to GND as GND is not connected to the top horizontal strip

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Re: Shift register showing all 1's / not working

Fri Oct 15, 2021 11:54 am

mahjongg wrote:
Fri Oct 15, 2021 11:28 am
as for the diagram above, If I read it right pin 13 (OE) is NOT connected to GND as GND is not connected to the top horizontal strip
Left hand black gnd wire is connected to top and bottom strip

LTolledo
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Re: Shift register showing all 1's / not working

Fri Oct 15, 2021 12:05 pm

mahjongg wrote: as for the diagram above, If I read it right pin 13 (OE) is NOT connected to GND as GND is not connected to the top horizontal strip
hmm... it would seem that way....since there pin39 (Gnd) is connected to the top Gnd strip...and at that same point connected directly to the bottom Gnd strip... (two wires in one point on the breadboard)

could be a sort of "mis-diagram" from the book "Raspberry Pi LED Blueprints" ;)
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Come to me with 'problems' and I'll help you find solutions"

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mahjongg
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Re: Shift register showing all 1's / not working

Sun Oct 17, 2021 2:40 pm

pidd wrote:
Fri Oct 15, 2021 11:54 am
mahjongg wrote:
Fri Oct 15, 2021 11:28 am
as for the diagram above, If I read it right pin 13 (OE) is NOT connected to GND as GND is not connected to the top horizontal strip
Left hand black gnd wire is connected to top and bottom strip
No it isn't!
The "rule" is that "corners" in the wire do not make contact with the breadboard contact strip below it. Only one wire can go in one breadboard "hole" at any one time, but yes I assumed you thought that it would, but it doesn't work that way!

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Re: Shift register showing all 1's / not working

Sun Oct 17, 2021 5:28 pm

mahjongg wrote:
Sun Oct 17, 2021 2:40 pm
pidd wrote:
Fri Oct 15, 2021 11:54 am
mahjongg wrote:
Fri Oct 15, 2021 11:28 am
as for the diagram above, If I read it right pin 13 (OE) is NOT connected to GND as GND is not connected to the top horizontal strip
Left hand black gnd wire is connected to top and bottom strip
No it isn't!
The "rule" is that "corners" in the wire do not make contact with the breadboard contact strip below it. Only one wire can go in one breadboard "hole" at any one time, but yes I assumed you thought that it would, but it doesn't work that way!
Sorry, of course you're right, you shouldn't have two wires in one hole on breadboard, I'm more a vero/solder person so couldn't see the problem. There is a colouring problem on the program that produced the diagram, the corners on black wire are marked with a black dot, the corner above the hole in question is marked green, it should be marked black.

ame
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Re: Shift register showing all 1's / not working

Sun Oct 17, 2021 7:21 pm

mahjongg wrote:
Sun Oct 17, 2021 2:40 pm
pidd wrote:
Fri Oct 15, 2021 11:54 am
mahjongg wrote:
Fri Oct 15, 2021 11:28 am
as for the diagram above, If I read it right pin 13 (OE) is NOT connected to GND as GND is not connected to the top horizontal strip
Left hand black gnd wire is connected to top and bottom strip
No it isn't!
The "rule" is that "corners" in the wire do not make contact with the breadboard contact strip below it. Only one wire can go in one breadboard "hole" at any one time, but yes I assumed you thought that it would, but it doesn't work that way!
You're technically correct, but it's a simple error in the drawing. The ground strips at the top and bottom of the breadboard are strapped together, then they are supposed to be grounded via pin 39. In the diagram two wires go into one hole, which is not possible in real life, however the intention is clear.

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mahjongg
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Re: Shift register showing all 1's / not working

Mon Oct 18, 2021 3:11 pm

It wasn't immediately clear to me, only after discovering that OE was floating I found out that it should have been connected to GND.
Sorry perhaps an ocupational deformation of me, I used to be a PCB (and later IC) Layouter, so `I'm used to seeking these kinds of errors, and such "simple errors" tend to lead to non working circuits. :mrgreen: :D

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