Using the same clock for multiple shift register

Sorry for the beginner question. I'm working on a nixie tube clock and I have a bunch of shift registers for each tube. Do I need to use a different clock for each IC or can I use the same clock for each register?

• Assuming you're using something similar to a 74HC595 shift register, then, yes, you can wire the same clock to all registers... up to a limit. Commented Apr 1, 2014 at 19:44
• I would be using 6 registers and thank you for the reply Commented Apr 1, 2014 at 19:45
• You can wire the 6 clocks together without a problem. You can also wire the latch pin of all of them together. Commented Apr 1, 2014 at 19:47
• But the other quick things is how would I control 10 numbers if there are only 8 output pins? And thanks! Didn't even thing about the latch piin. Commented Apr 1, 2014 at 19:47
• I'll make that an answer if you don't mind. Commented Apr 1, 2014 at 19:48

Assuming you're using something similar to a 74HC595 shift register, then, yes, you can wire the same clock to all registers.

There's a limit, but it is far more than the 6 shift registers you want to use, so you can safely wire the 6 clocks together without a problem.

You can also wire the latch pin of all of them together.

If the device you need to control has 10 inputs, then you must string more shift registers together and allocate the first register to the first 8 inputs, and the remaining 2 to the second and so on.

So, calculate how many inputs you'll have in total, and then string together the corresponding number of shift registers.

Does that make sense to you?

• That makes sense. It would make more sense to use a 16 bit register then. Commented Apr 1, 2014 at 19:59
• Well, I'd use whatever is easier for you. I have plenty of 595's in my bins and I'm really familiar with them so I'd use them. Since you can string them together, then it doesn't really matter if you have 8 or 16 bit registers. Unless you have board design constraints or something like that. Commented Apr 1, 2014 at 20:03
• @evan.stoddard Note that if you are building a clock, all of your digits are not 0 through 9, so you will not need 60 output pins for a 6 digit clock. You will find that you need fewer 8-bit shift registers than the 6 you anticipated. I'll leave the actual count to you.
– Tut
Commented Apr 1, 2014 at 20:05
• @Tut Thank you. Didn't even think about that... the only issue I have with that is cathode poisoning. I don't want to burn out only one or two numbers on the tubes. Commented Apr 1, 2014 at 20:09
• @Ricardo, what is the limit to how many shift registers you could hook up to the clock line, and how would you calculate that? I am working on a project that requires ~100 shift registers, and want to know if I will run up to a limit. Commented Apr 13, 2015 at 17:44