#001 7-Segment Direct Drive

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

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

Notes

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:

Construction

Credits and References

• SC56-11 Datasheet
• Arduino and 7 Segment LED - original idea and source code
• Drive a 7-Segment LED with an Arduino
• ..as mentioned on my blog