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Project Notes

#177 LED7Segment/ShiftDrive

Test control of a 7-segment display via a 74HC595 shift register.

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



While you can wire up each segment pin to a digital out on the Arduino as in the LED7Segment/DirectDrive project, it soon becomes pretty wasteful of pins. This project uses a 74HC595 8-bit shift register to feed segment values, requiring only 3 pins.

Since the 74HC595 has latched outputs, it also means all segment changes are simulataneous.

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

However the code uses bytes to represent dp,G,F..A from MSB to LSB, so I use MSBFIRST transfer.



The Schematic

The Build

Credits and References

About LEAP#177 7-SegmentCMOS/TTLArduino
Project Source on GitHub Return to the LEAP Catalog

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

LEAP is my personal collection of electronics projects, 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 (IMHO!).

The projects are usually inspired by things found wild on the net, or ideas from the sources such as:

Feel free to borrow liberally, and if you spot any issues do let me know. See the individual projects for credits where due. There are even now a few projects contributed by others - send your own over in a pull request if you would also like to add to this collection.