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Topic: 7-Segment LEDs and Shift Registers (Read 1 time) previous topic - next topic


May 18, 2012, 05:47 pm Last Edit: May 18, 2012, 08:36 pm by badnuzjr Reason: 1
I'm going to lay this out with it being known that I am new to all of this small electronics stuff.  programming I can do, wiring ... well I'm asking for help aren't I.

I play an online racing simulator, iRacing.  I want to build an electronic scoring tower like they have at the race track.  I am going to use 7-segment LED's, shift registers, and arduino uno.  I used this design as my starting point: http://www.sqlskills.com/blogs/paulselec/post/Arduino-cascading-shift-registers-to-drive-7-segment-displays.aspx

Here is my concept:

I have someone who was helping me get the board put together.  Here is the design I gave him:
Here is the design he sent back: http://nuzumphoto.com/Unused/iracing/scoringtower/Tower3-1.pdf

The LED's used: https://www.kingbrightusa.com/images/catalog/SPEC/ACSC56-41SRWA-F01.pdf
The Shift Registers used: http://www.nxp.com/documents/data_sheet/74HC_HCT595.pdf

So now I have the actual board in my hands and have it hooked up.  ran the exact program from the sqlskills.com site.  nothing.  When i initial plug in the board to USB the LEDs flash red across them.  Like it's clearing them or something.  But the program does nothing.  No reaction at all from the board.

Photos of the board and setup.

Anything glaring that I missed between the original design and mine.  Any thoughts at all?


USB only puts out 500mA.
Is that enough current for all those LEDs?
23 digits x 7 segments/digit x 14.3ma/segment = way more than 500mA.
(  (5V-1.85V)/220 = 14.3mA )
Vled-forward = 1.85 typical to 2.5Vmax, lower works to worst case, higher current flow)
Designing & building electrical circuits for over 25 years. Check out the ATMega1284P based Bobuino and other '328P & '1284P creations & offerings at  www.crossroadsfencing.com/BobuinoRev17.
Arduino for Teens available at Amazon.com.


Like the other poster said - too much current is needed.

Hook the boards up to an external power supply that's able to power it all. It's a good test to ensure this is the problem!

If you don't want a power adapter in your design, consider using multiple USB plugs - like the old USB hard-disk's had.

I noticed there's one common resister for all the segments in the display. How have you avoided a change in LED brightness as the number of segments illuminated changes?


I have actually only started testing it with one 4-LED board.  If you go to the flickr (http://flic.kr/s/aHsjzsbo73) photos you will see what the setup currently looks like. 

Do you think just the four LEDs would need an external power supply?  I have no problem with adding one.  I've had to do so with my other projects.

Like this one: http://www.youtube.com/watch?v=HpXlL0OYhrU&feature=g-upl

I there are 4 capacitors and 4 resistors in the design.  The photos from flickr show that much better.

I appreciate the help.  As I said, i'm much more of a programmer than I am an electronics tinkerer.

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