I'm fairly new to electrical circuitry, and while trying to test out and use a 74HC595 Shift register I ran into some issues. I'm not using a micro-controller, just push buttons to control to the register. The lights will flicker and the controls will not do what they are supposed to do. Pressing the latch button turns off the LEDs until I start it again 5 minutes later. I have a feeling that the circuit is being over-driven, but I could be wrong. Anyone have any idea what im doing wrong and how it can be fixed? Thanks.

Here's the circuit board. It is hooked up to 5V on either side of the breadboard. That apparatus with the BJT and the LED is a NOT gate to control the clear function on the Shift Register.

enter image description here

  • \$\begingroup\$ Just a note the LEDs may be backwards in the diagram but they are correct in the actual circuit \$\endgroup\$ – Mrosky Dec 30 '18 at 1:47
  • \$\begingroup\$ Add a debounce circuit to the clock pin into the shift register. \$\endgroup\$ – Dwayne Reid Dec 30 '18 at 1:56
  • \$\begingroup\$ You will get a much better response here if you show us a proper schematic rather than a pictorial wiring diagram. It's very difficult to tell what you are trying to do around the NPN transistor. But, as @DwayneReid said, it is likely that you have problems with switch bouncing. \$\endgroup\$ – Elliot Alderson Dec 30 '18 at 2:51

First thing I notice is that you have no connection between the + and - busses on the left side of the breadboard, and the corresponding busses on the right - if you want those busses connected together, you must add jumper wires - the breadboard doesn't provide a connection.

You appear to want the switches to pull the '595 inputs to +5V when pressed. You will need pull-down resistors (10K or so will do) from the inputs to Ground to pull the inputs low when the switches are not pressed. CMOS logic inputs, as in the 74HC or AC parts, are very high impedance, and will float randomly between High and Low, unless pulled to one state somehow.

Large breadboards often have breaks in the long "power supply" busses in the middle of the board - you need to add jumpers over those breaks to make the busses run the full length of the board.

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  • \$\begingroup\$ The circuit doesn't exactly match what I have, but power is going to both sides of the breadboard in the actual circuit even though the picture doesn't show it. I added resistors from all the input switches to ground to pull them down but it isn't changing any of the results. \$\endgroup\$ – Mrosky Dec 30 '18 at 2:17
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    \$\begingroup\$ @Mrosky: we assume that what you show is what you actually have, so you should show how things are REALLY connected. You should also show a schematic diagram - much easier to understand the actual circuit with a schematic than with a "cartoon drawing" as you provided. There is a schematic editor here - press "Control M" to open it. \$\endgroup\$ – Peter Bennett Dec 30 '18 at 2:22
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    \$\begingroup\$ "The circuit doesn't exactly match what I have"...are you kidding? @PeterBennett wasted time trying to diagnose your problems because you couldn't provide a correct schematic? \$\endgroup\$ – Elliot Alderson Dec 30 '18 at 3:29

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