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Project Notes

#001 LED7Segment/DirectDrive

Test direct control of a 7-segment display, performing a countdown from 9 to 0.

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



The 7-segment display unit I have is stamped “SMA42056”. It appears to be fairly common, however I’ve yet to find a datasheet for it. From inspection hwoever, it’s clearly a common cathode unit, and similar to the the SC56-11

There are two common cathode pins, but since these are internally connected there is no need to connect both to ground. Lighting a segment simply means providing a driving voltage to the corresponding anode pin.

This circuit puts the resistors in series of the anode pins. This ensures a consistent brightness no matter how many segments are on. Note that it is possible to put the current-limiting resistor on the common cathode; this is a bit of an approximation and will lead to varying LED brightness but may be “good enough” depending on your application.

Pin-Segment Mapping

Here’s a summary of how the Arduino pins are mapped to LED segments:

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


The Breadboard

The Schematic

The Build

Credits and references

About LEAP#1 7-SegmentArduino
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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.