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Project Notes

#199 7-Segment CD4026 Bucket-brigade

A CD4026 bucket-brigade for driving multiple 7-segment LED displays

Here’s a quick video of the circuit in action:



The CD4026Drive project explored the CD4026 as an easy way to drive a 7-segment display. This project simply extends the idea for driving multiple digits.

It just requires the carry-out from the first CD4026 to be chained as the clock input for the second. Here I’ve wired up two digits, but can be replicated for any number of digits.

A second GPIO pin is used to control the reset.

Note that in my breadboard build, I cheated on the current-limiting resistors: placing a single 220Ω on each LED digit cathode rather than a 220Ω on each segment anode as per the schematic. Using a single anode resistor works fine - the downside being that segment brightness will consequently vary to a degree depending on how many segments are on.



The Schematic

The Build

Credits and References

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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.