Common Ground For 7 Segment Display?

Thread Starter

JDR04

Joined May 5, 2011
367
Hi Folks, could somebody help me with connecting my Common Cathode 7 segments displays up please?

I have six of them which are driven by 4026B ic's.

Can I link all the Cathodes together and then have one connection to ground? Or must each one be connected to ground individually.

I have linked pins 3 and 8 of each display together and then linked them to the next pins 3+8 and so on and then finally the last one thought a 10K resistor and to ground.

Your help will be greatly appreciated.
JDR04
 

#12

Joined Nov 30, 2010
18,224
You're making me crazy here. Need a drawing. Can't imagine why you'd put 10k in series with your ground line.
 

Thread Starter

JDR04

Joined May 5, 2011
367
Thanks for your reply.

As a newbie I rely on other peoples advice and was told to insert a 10K resistor to protect the 7 segment displays?

I have done a drawing of how I connected the 7 segment displays together. Hopefully it makes things a bit clearer. Your time and advice is appreciated. Many thanks JDR04
 

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bertus

Joined Apr 5, 2008
22,270
Hello,

Do you have the specs for the dispalys?
A datasheet would be perfect.

Also a COMPLETE schematic is welcome.

In your other thread ( Anyone Built This CD4033 Counter Circuit? ) you can see that the cathode is bound directly to ground.
Each segment of the display has a transistor and a current limiting resistor.

Bertus
 
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SgtWookie

Joined Jul 17, 2007
22,230
No, you cannot connect them like that.

All of the common cathodes should be connected to ground.

Each connection from each 4026 output to the 7-segment display inputs requires a resistor.

You haven't told us what displays you are using, or what voltage you are operating the circuit with - so until we get that information, we can't tell you what resistors you will need to use.

[eta]
Bertus beat me to the reply, but I've attached an example of how to connect the 7-segment displays using resistors. You can get resistor networks in 14-pin DIP configuration, which makes them quick to connect up.

I've shown the resistors as 330 Ohms, but that may not be correct for your 7-segment displays and voltage you're using.
 

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Thread Starter

JDR04

Joined May 5, 2011
367
Thanks Bertus and SgtWookie for your replies.

Your questions made me ponder what I had done and have pointed me in the right direction. I've got displayus up and running and will expand them one by one.

I'm still unsure of the common ground bit for the dispalys though:confused:

The two I have up and running are Common Cathode 7 segment displays. First I connected pins 3 and 8 of each display up to ground individually and it worked. Curiosity got the better of me though and I removed each connection from pin 3 to ground and the displays still worked? Oh, I also removed the 10K resistor as well. So, with reference to the common ground situation I done something that will in the long term cause damage to the 7 segment displays or will it be OK?

http://docs-europe.electrocomponents.com/webdocs/0200/0900766b802001c1.pdf

Above is the datasheet for the 7 segment display.

Thanks for your help Guys JDR04
 

SgtWookie

Joined Jul 17, 2007
22,230
I've got displays up and running and will expand them one by one.
Good news. :)

I'm still unsure of the common ground bit for the displays though :confused:

The two I have up and running are Common Cathode 7 segment displays. First I connected pins 3 and 8 of each display up to ground individually and it worked. Curiosity got the better of me though and I removed each connection from pin 3 to ground and the displays still worked?
Look in the datasheet; you will see that pins 3 and 8 are connected internally. This is not always the case; sometimes they are individual grounds; for example one might ground segments f,a, b, and g, and the other segments c, d, e, and the dp. I had some displays like that.

Oh, I also removed the 10K resistor as well.
Good, otherwise they would be very, very dark!

So, with reference to the common ground situation I done something that will in the long term cause damage to the 7 segment displays or will it be OK?
They'll be OK.

Thanks for the link to your displays' datasheet; that always helps a great deal.
 
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