All About Circuits Forum  

Go Back   All About Circuits Forum > Electronics Forums > General Electronics Chat

Notices

General Electronics Chat Discussion forum for general chat about anything electronics related, including asking questions about material in the All About Circuits E-book, Worksheets, and Videos.

Reply   Post New Thread
 
Thread Tools Display Modes
  #1  
Old 08-29-2009, 05:17 PM
jlon jlon is offline
Junior Member
 
Join Date: Aug 2009
Posts: 13
Thumbs down common cathode LED display limiting resistor?

I'm want to design a circuit with some 7-segment LED displays driven from a 4511 or some variant. Now, I haven't burned up anything in quite some time. So before I burn anything up, I'm wondering:

Is it okay to put a single current-limiting resistor on the common cathode, or is it a necessity to have a separate current-limiting resistor on each LED segment? Can someone experienced in this give me a hint?

Joe
Reply With Quote
  #2  
Old 08-29-2009, 05:18 PM
Mike2545 Mike2545 is offline
Senior Member
 
Join Date: Mar 2009
Location: Toledo, USA
Posts: 116
Default

You will need a separate resistor for each segment.
Reply With Quote
  #3  
Old 08-29-2009, 05:43 PM
hgmjr's Avatar
hgmjr hgmjr is offline
Super Moderator
 
Join Date: Jan 2005
Location: Tennessee, USA (GMT-6)
Posts: 9,030
Blog Entries: 11
Default

I too recommend you go with a resistor per segment. If you try to get away with one resistor, you will find that the brightness of the segments will change as a function of the number of segments you have illuminated at any one time.

hgmjr
Reply With Quote
  #4  
Old 08-29-2009, 05:45 PM
jlon jlon is offline
Junior Member
 
Join Date: Aug 2009
Posts: 13
Default thanks!

That's going to be lot of resistors, but I don't want the display to change in intensity. So thanks to all!

Joe
Reply With Quote
  #5  
Old 08-29-2009, 08:41 PM
rjenkins rjenkins is offline
Senior Member
 
Join Date: Nov 2005
Location: Sheffield, England
Posts: 1,015
Default

If you are multiplexing several digits, you only need one set of segment resistors as only one display is actually drawing current at any time.
__________________
Robert Jenkins.
Reply With Quote
  #6  
Old 08-29-2009, 11:03 PM
Bill_Marsden's Avatar
Bill_Marsden Bill_Marsden is offline
Super Moderator
 
Join Date: Mar 2008
Location: Dallas, TX (GMT-5 w/ DST)
Posts: 18,802
Blog Entries: 5
Default

If you research it they make 7 resistor arrays, in a 14 pin DIP package. Resistors are cheaper though.
__________________
..
"Good enough is enemy of the best." An old engineering saying, Author unknown.

General info:
If you have a question, please start a thread/topic. I do not provide gratis assistance via PM nor E-mail, as that would violate the intent of this Board, which is sharing knowledge ... and deprives you of other knowledgeable input. Thanks for the verbage Wookie.
Reply With Quote
  #7  
Old 08-30-2009, 01:32 AM
jlon jlon is offline
Junior Member
 
Join Date: Aug 2009
Posts: 13
Default

Yes, I've seen the resistor arrays. I'd rather just solder some 0805 packages. Not hard at all and much cheaper, lots of flexibility in positioning.
Reply With Quote
Reply   Post New Thread

Tags
, , , , , ,


Related Site Pages
Section Title
Worksheet Digital display circuits
Textbook 7-segment display : Digital Integrated Circuits
Textbook Special-purpose diodes : Diodes And Rectifiers


Similar Threads
Thread Thread Starter Forum Replies Last Post
Led or dot matrix display james_lynch General Electronics Chat 1 06-22-2009 08:31 PM
running message led display maxxwheeler Programmer's Corner 3 03-22-2009 05:14 PM
I'm confused with voltage/current in my first LED array Fixxxer The Projects Forum 22 01-28-2009 03:10 PM
Needing a series-parallel combination resistor circuit calculator jasonbengiat The Projects Forum 1 03-13-2007 08:47 PM
LED Dimming in Parallel pfhorge The Projects Forum 6 02-27-2007 07:36 PM

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump


All times are GMT. The time now is 09:23 PM.


User-posted content, unless source quoted, is licensed under a Creative Commons Public Domain License.
Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2014, vBulletin Solutions, Inc.