7 segment display hums

I am building a simple 2 number, 7 segment display. I bought two of the 7" 7 segment displays from Sure Electronics. They're sweet! and easy to run from an Arduino. However, the displays hum when connected to the battery. Is that normal??

Using a 12v 5aH sealed battery and the displays are powered through the + - aux power connections, power to the second display is fed from the output aux port on the first to the input of the second.

I didn't notice any hum during testing when power them via the Arduino that was powered from a 12v wall wart.

Should I have a ground or component or something between the battery and the display?

Thank you!

Can you sketch your wiring?

Hi, can you supply us with a diagrams, one with wallwart (horrible name for a generic horrible product, at least they aren’t being called power supplies, they are far from it) and another with battery.
Before you post the diagrams view them and check that part numbers are clear.
Tom.

i don't have a sketching app, but basically it's like this:

battery ground --> display1 ground in battery positive --> display1 12v in

display1 ground out --> display2 ground in display1 positive out --> display2 positive in

Link to the datasheet for the display would be useful - for instance it might have an on-board SMPS which are known to whine sometimes.

darrenmathews: i don't have a sketching app, but basically it's like this:

"but basically" = ambiguity

Pencil, paper; sketch it out, take a picure of it, post same

the displays hum

Maybe it has forgotten the words.

darrenmathews: i don't have a sketching app, but basically it's like this:

Do you have a Paint program? Practically every modern PC comes with one.

If you are using Windows, Express Schematic is a great, free, program:

http://www.expresspcb.com/ExpressPCBHtm/Free_schematic_software.htm

I use it for all the schematics I post here.

Humming huh.....

The only thing that generally hums in any circuit are inductors/transformers