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