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8-bit series to paralell-out shift register SN74LS164N

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New Member
I'm just getting back into electronics, I played around with it long ago, and need a little help with an 8-bit series to paralell-out shift register.

I have a SN74LS164N 8-bit shift register.
SN74LS164N pdf, SN74LS164N description, SN74LS164N datasheets, SN74LS164N view ::: ALLDATASHEET :::

I'm trying to send a pulse from a 555 timer to step the register.

On the chip pins 1 and 2 are the data input. I think I have to jumper the two and use the output of the 555 timer (pin 3) to send a signal to the connected pins 1 and 2. Each time the 555 timer sends a pulse to pin 1 and 2 the bit should shift to the next Q# pin on the 8-bit register.

Pin 14 is the 5 volt postive pin and pin 7 is the common or ground.

My question is about pin 8, which is the clock. Can I leave this pin unconnected or does it have to have a voltage applied to it? I'm not sure of its function other than maybe how fast the data shifts. But wouldn't that be controlled by the 555 timer sending a signal to pins 1 and 2?

For the reset pin, # 9, can I leave that unconnected?

Also, if anyone has a simple circuit design using this chip I'd be enternally greatful!

Thank you,


New Member
What exactly are you trying to accomplish? Is the SN74LS164N something you just had laying around? There may be a better chip to suit your needs. No you can't leave the CLK pin unconnected, if you did the chip would never do anything except reset. The CLK does control how fast the data shifts but it also controls shifting in the data. if both inputs A and B are logic high 1 when the CLK input transitions from low to high then bit 1 Q0 will equal 1. should A or B be low when the CLK pin transitions low to high a 0 would be carried to bit 1 Q0. Say you had A and B high, toggled CLK low to high then low again, bit 0 Q0 would equal one, toggle CLK again and bit 1 now reflects A and B and bit 2 Q1 now equals what Q0 was before the second CLK transition.

In almost all cases IC inputs cannot be left floating or unconnected. Reset needs to be tied high (positive) for the chip to function and low to reset the chip.

If you can provide more details on your project we could help you more. There are so many ways to do what it seems you're trying that we need more info from you.

:Edited for spelling.
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New Member
Thanks so much jimlovell77 for the your reply.

Yes, I do have some SN74LS164N that I wanted to play around with.

I know there are probably better ways to do what I'm trying to but, since I have some 555 timers, some SN754410NE Quad Half-H Drivers and the SN74LS164N ICs I thought I see if I could run a 3 phase brushless DC motor, (hard drive motor), with them.

I'm sure it won't be efficient since there would be some breaking going on but, I still should be able to turn it in a semi good fashion, I think.

I trying to send a pulse from the 555 timer to the shift bit register and use the that to feed the quad half-h driver. The quad half-h driver is only rated a 1amp which is a little low. Is my plan doomed?


New Member
Is there specific part of the page linked you don't understand or can't follow? Granted I just glanced at it but you should be able to use the schematics shown. Just substitute the L293D with your SN754410NE chip. I've never used either chip but a very quick look at the relating datasheets shows the parts to be functionally and pin for pin identical. Let me know where you're stuck following the guide and I'll chime in with what I can.

Great site by the way, I'm a member there. There are a lot of very creative (and well funded!) contributors.


New Member
Thanks jimlovell777.

I think you gave me all the information I need. I really appreciate your help.

Yes, this is a great site. I'm sure I be needing some help from some of the contributors as I play around a little more with electronics:)

Thanks again jimlovell777!
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