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Project Notes

#635 CD4001 SR Latch

Set-Reset latch implemented with CD4001 NOR gates.

Build

Here’s a quick demo..

clip

Notes

This circuit is another implementation of a Set-Reset flip-flop, this time using NOR gates. Sometimes this is referred to as a “NOR Latch”. A CD4001 is used to provide the two NOR gates required.

See the LEAP#061 SRLatch circuit for an implementation using BJTs.

Ben Eater has a great video explaining SR latch behaviour:

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Truth Table

Set(t) Reset(t) Output Q(t+1)
0 0 no change
0 1 0
1 0 1
1 1 invalid state

Construction

bb

schematic

Build

Credits and References

About LEAP#635 Digital LogicCMOS/TTL
Project Source on GitHub Project Gallery Return to the LEAP Catalog

This page is a web-friendly rendering of my project notes shared in the LEAP GitHub repository.

LEAP is just my personal collection of projects. Two main themes have emerged in recent years, sometimes combined:

  • electronics - usually involving an Arduino or other microprocessor in one way or another. Some are full-blown projects, while many are trivial breadboard experiments, intended to learn and explore something interesting
  • scale modelling - I caught the bug after deciding to build a Harrier during covid to demonstrate an electronic jet engine simulation. Let the fun begin..
To be honest, I haven't quite figured out if these two interests belong in the same GitHub repo or not. But for now - they are all here!

Projects are often inspired by things found wild on the net, or ideas from the many great electronics and scale modelling podcasts and YouTube channels. Feel free to borrow liberally, and if you spot any issues do let me know (or send a PR!). See the individual projects for credits where due.