Segments light when they should be off

Hello,

I am multiplexing a 12 volt 7 segment led using a SN74HC595 shift register and a ULN2003 darlington array.

Segments that should be off are dimly lit.

For instance if I am displaying a two A,B,D,E,G are lit as expected but C and F are dimly lit as well.

i have measured the voltage at the input pins on the darlington and pins that should be high are high and pins that should be low are low.

Any help will be greatly appreciated.

You need to post both your schematic and code, use the correct code tags. If you don't know what that means read the how to use this forum sticky post.

I will post the code once I have cleaned up the fluff and copious commented out lines

Have you not got a schematic? It is difficult to follow a physical wiring diagram. The bit round the transistor does not make any sense. What should it be?

The Gnd pin (8) of the UNL2003A does not appear to be connected to logic ground.

When I connect ULN2003 GND to logic ground it does not light at all.

I have posted a new picture of the schematic.

Kreplach: When I connect ULN2003 GND to logic ground it does not light at all.

Then you have something else wrong. You can not switch a 12V anode like that. You need to source current through the anode with a PNP transistor. That is still not a schematic so don't say you posted one when you have not.

Kreplach:
I have posted a new picture of the schematic.

A schematic looks like this:

What you have posted is not much more informative than a photo of your board.

When I connect ULN2003 GND to logic ground it does not light at all.

Not in your revised picture you haven’t.

Nick,

You put on the right path.

When I connected the shift register ground to the 12 volt ground path instead of the 5 volt ground back to the arduino it works as expected.

I will work on furnishing better schematics so that the community will be able to offer help without having to guess at what it is I am trying to accomplish.

Thank You..

The two grounds should be connected together anyway!