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When I connect my Arduino with this 74HC595 shift register circuit, all the shift register's outputs go high, and any code I run doesn't seem to change this. Regardless of what I run, all outputs are still high.

I have tried connecting the output enable pin to high (by plugging it into 5 V power) in order to clear all outputs, but that changes nothing.

I have also tried running a simulation of an Arduino using the same circuit I built in person via this website, and it worked perfectly as I expected.

This is what my circuit looks like:

  • Red connects to 5 V
  • Orange connects to 5 V on the Arduino
  • Black connects to ground
  • Blue connects to clock pin
  • White connects to latch pin
  • Yellow connects to serial data input
  • Greens connect to LEDs
  • I'm using 330 Ω resistors for this circuit

overhead view of circuit

angled view of circuit from front

angled view of circuit from back

connections to arduino

Connecting output enable pin to 5V: connection of output enable pin to 5V

I'm not sure what's causing this problem, especially as this is occurring before any code is run, so I'm assuming it's a circuit problem, and I'm not too familiar with it.

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  • \$\begingroup\$ It makes no sense. OE high should disable outputs and LEDs should turn off. Make sure the chip is a 74HC595 and it is not damaged. \$\endgroup\$
    – Justme
    Sep 30, 2022 at 5:06
  • \$\begingroup\$ @dispointmnt : Are you still having problems with this circuit? Have you verified all your connections and/or replaced the 74HC595 chip? Note that even the bread board device could have problems after years of usage, the sockets are susceptible to accumulated dust, broken off pins, even solder balls falling into them. If you troubleshoot the circuit try checking the signals (voltage levels) directly at the chip pins to avoid missing any open connections along the path. \$\endgroup\$
    – Nedd
    Oct 1, 2022 at 3:16
  • \$\begingroup\$ Justme, The chip says "SN74HC595N" on it, so I hope it's the right one, and I suspect it is damaged, but I have no idea how to check. @Nedd Yeah I'm still having grief with this circuit, I've verified all my connections to ensure everything is up to scratch, and I can't replace the chip because I don't have a spare, I'm going to borrow a friend's to see if anything changes, but I suspect my current one is broken or damaged in some way. Also my breadboard is almost new, I only got it a few months ago, so I don't think its the breadboard. Thanks for replying \$\endgroup\$
    – dispointmnt
    Oct 1, 2022 at 6:45
  • \$\begingroup\$ @dispointmnt: Be aware these are CMOS parts, a moderate static zap could fry it. If working in a dry area you may also want to use a static strap. Consider ordering spare chips before borrowing. If you haven’t found the reason the first part went bad there’s a chance the next part suffers the same fate. Try building the circuit first with only the power connections, (no signal lines), then test it in stages (like setting the ~OE hi & lo) to verify functionality, perhaps even use one LED at the start. With only a few connections added at a time you may minimize the chance of making any errors. \$\endgroup\$
    – Nedd
    Oct 1, 2022 at 8:39

2 Answers 2

Reset to default
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I could answer more if you drew a schematic (please do so, and I'll expand or change this answer as appropriate), but the first thing that comes to mind is: The '595 does not appear to make any claims as to what its outputs will be when first powered up. They could power up into any state.

That's why you have the reset pin, labelled as ¬MR (or MR with an overbar, or ~MR). Driving this pin LOW will reset all outputs to low, and driving it HIGH will enable normal operation. Leaving it floating is not recommended. (Floating inputs tend to drift high in 74LS series chips, but can do anything in 74HC series ones, and will pick up noise from the environment quite easily.)

Try driving the reset pin low, then return it to high, and see if the LEDs turn off. If they don't, it's possible something is wired wrong. But as you've not drawn any schematic, nor given a clear diagram of what wires are connected where, I can't really go any further with that train of thought at the moment.

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    \$\begingroup\$ From what I've read the so called Master Reset (aka: MR or SCLR) pin only clears the internal registers, you still need to clock the output (latch) to get the data onto the output pins. \$\endgroup\$
    – Nedd
    Sep 30, 2022 at 6:50
  • \$\begingroup\$ Yep, I've tried to reset the MR pin by connecting it to low and back to high, but the leds stayed on the entire time. Here is a schematic of what I tried to build imgur.com/a/jg9jX5K \$\endgroup\$
    – dispointmnt
    Oct 1, 2022 at 6:36
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See this link .
See also this link Example board using 595 for 4 digits multiplexing display.
And the examples file .

I have simulated this circuit with two 74595 parts.
Made with microcap v12. Link

It works "well" if one follows this schematic.
I have however noted that something is "wrong" with OE.
Does not work as it would do. Model problem.

enter image description here

However, will check with some Arduino boards using it or similar.

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  • \$\begingroup\$ Yeah, I used the first link to build my circuit in the first place, and I think I've followed it to the letter, but it still doesn't work. I'm not quite sure what the second link is supposed to be showing. And I've tried to use already working code on my circuit I found lying around online, but none of them seem to change anything in my circuit. \$\endgroup\$
    – dispointmnt
    Oct 1, 2022 at 6:40
  • \$\begingroup\$ Second link is just an example of board using 2x 74595 for multiplexing display 4 digits. \$\endgroup\$
    – Antonio51
    Oct 1, 2022 at 7:33
  • \$\begingroup\$ @dispointmnt Did you add a decoupling 100nF - 1uF capacitor between Vcc and Gnd (nearest) of the 595? \$\endgroup\$
    – Antonio51
    Oct 1, 2022 at 7:39

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