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Project Notes

#081 4x7-Segment Double Shift With FETs

Driving a 4-Digit 7-Segment LED display with only 3 pins, using two 74HC595 shift registers and some n-channel FETs

The Build


This circuit is a variation of the DoubleShift experiment that demonstrated how to use two 74HC595 shift registers and some NPN BJTs to drive a 4-digit 7-segment display with only 3 Arduino GPIO pins.

The only difference here is that the S9013 NPN BJTs are replaced with 2N7000 n-channel FETs.

When fully on (e.g. displaying 8888), it appears the display and associated components on the breadboard are drawing an average of about 2.47mA (compared to 2.87mA with BJTs).


The Breadboard

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.