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#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

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