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Project Notes

#178 7-Segment Shift Drive Module

A custom 7-segment LED display module PCB with 74HC595 shift register interface.

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



This is my version of project 2 from the KiCad like a Pro course from Tech Explorations.

It is essentially the LED7Segment/ShiftDrive project but as a custom PCB. The PCB includes a single 7-Segment LED, current limiting resistors and 74HC595 shift register.

The PCB design was done with KiCad.

I sent these off for production at OSH Park, and they arrived (in Singapore) a month later (Jan 17th -> Feb 17th). They turned out quite well, certainly no issues with the fab.

After examining the PCBs, I found a few things that could be improved in the design:

  • doh! I got the data/latch labels around the wrong way (fixed in 1.1.0)
  • pin header label was obscurred by R1 (fixed in 1.1.0)
  • the thru-hole pads for the resistors are super-chunky compared to the other component holes. Not a real issue - just looks weird.
  • orientation of the 74HC595 should probably be a clearer (like a notch in the footprint outline)

But they work just fine!

Register-Pin Mapping

Here’s a summary of how the bits in the shift register are mapped to LED segments:

Bit Segment
0 A - top horizontal
1 B - top right vertical
2 C - bottom right vertical
3 D - bottom horizontal
4 E - bottom left vertical
5 F - top left vertical
6 G - center horizontal
7 dp - decimal point

Test Script

The ShiftDriveModule.ino sketch drives the module with a simple counter from 0-9, with the decimal point lit for even numbers.

The script manipulates the data/latch/clock output directly (no SPI), and assumes the following pin connections:

Arduino Pin Module Pin
5V Vcc



See the KiCad project for all the details. Here’s the result:

The Schematic


PCB render

Here are the finished boards. For the one I’ve already soldered I first used male pins (to plug-in to a breadboard), but if I do another I’ll probably use female pin headers instead.


Credits and References

Order from OSH Park</img>

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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.