I've a problem with this circuit, it should drive 2 (or more) big 7-segment display using a MAX7219 and the relative Arduino's library. It uses ULN2003 and UDN2981 to use +12V and a series of 5 led per segment (in the image I simplify with only one led for segment). The CD40106 is used as logic NOT…

Multiplexing a big 7-seg display with MAX7219

CrossRoads September 26, 2013, 5:32pm 2

Look at the output drive specs of the CD40106 vs the input drive current requirement of the ULN2003.

The CD40106 is really marginal to drive the ULN2003.
Find a better part.

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