#177 7-Segment Shift Drive

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

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

Notes

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:

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

Construction

Credits and References

• LED7Segment/DirectDrive - similar circuit but with direct control
• 74HC595 Datasheet
• SC56-11 Datasheet
• Drive a 7-Segment LED with an Arduino