« Hellenbach, Germany | Main | LED Animation Design: Dispatching »



Very cool video! Watching it I thought it would be fun to place the matrix at the end of a tunnel of mirrors for a kind of kaleidoscope effect.

og style

I was looking at the schematic and I was wondering what the resistor values were?


In the version I actually built (pictured above), I don't have any resistors between the PIC chip and the transistors, and used 220 ohm resistors between the 2N3904 transistors and the LED columns. This has been working great.

From what I read in the Microchip docs, they recommend 2K resistors between the PIC and the transistors, so I have been doing that in my new designs.

For the resistors between the transistors and the LED columns, you want (5v - V.led)/(I.led). If the drop (V.led) of the LED is 2v, and the current (I.led) is 20ma, then R should be 150 ohms. This is the most conservative number. Since the LEDs are multiplexed, you should be able to drive the LEDs with more current. Check the specs.

I also recommend building it on a breadboard first. Please let me know if you build it. I can post your picture here.

Good luck, David

OG Style

Thanks for the info on the resistors. I am going to try to build it. I belive I have all the parts. I just have to dubble check on the transistors.
Thinks again. Nice job on it.


If you have a regulated power supply, then you don't need the LM7805 or the capacitors. This is what I am using in the pictures above. Let me know if you have any questions or any problems.

OG Style

I have build the frame for the led's. I was wondering if you by any chance know of a place that I can cross reference the transistors at. I used to use a site but it went down. If now that is ok, I have some that I think will work fine.


The 2N3904 (on the columns) is an NPN general purpose amplifier. The 2N3906 (on the rows) is a PNP.

OG Style

Well I finished it. The only problem I have is the lights don't fade out. At the start of the program the leds should follow each other on and off. Mine does not do that. I put bigger resistors in from the transistor to the columns and rows. That did not change it. The only thing I can thing of doing is changing the leds. Any ideas??


Do the lights go out at all? Or do they just stay on? Do they go on in order?

OG Style

They are going on/off in different patterns. They are no runing the same pattern as yours are. I have just check all my connections and rows / columns and they are all correct. I have even chaned my leds still no go.

og style

If you can send me a email I will send you a video of what it is doing.


Here are some ideas to help figure out how we can make it work:
1. You can put a video on youtube
2. You can put some pictures on flicker
3. You can email me some pictures
4. I can make a new version of the program that firsts tests each LED, then tests each row, then tests each column.
Which do you want to try?

og style

I can send you a video and also if it is easy I will try a test pattern. I am good with hardware but I have never figured out how to program the pic chips. Thanks for the help

OG Style

Here is the video of it in action "http://rapidshare.com/files/119468426/100_6940.MOV.html" Let me know what you think. Thanks


I can't see the video. The site says that the download bandwidth is exceeded. I uploaded a version of the crossbar code that will test the LEDs. BUT I haven't tried to run it -- I hope it works! http://thevaportrail.com/projects/crossbar_led_test.zip

OG Style

The download bandwith is exceeded means your IP has the max allowed for the time frame. I will up it to a different place. And I will try the test. Thanks for the help

og style

Here is what I found the Rows with the 2n3906's are on when they should be off and off when they should be on. I am using this part "http://www.radioshack.com/product/index.jsp?productId=2062585&cp="


That's how much I don't know about transistors! I built the original with NPN instead of PNP. I uploaded a new version of the code here. I included both the LED test hex file and the regular hex file. The assembly is the same (look for the line that says "#define LED_TEST_BUILD"). -- http://thevaportrail.com/projects/crossbar_fix.zip

og style

That made a difference. Thanks for the help. Will get pictures and video to you when I am done

OG Style

Do you have a email address I can send you pics and videos at?



OG Style

I sent you pics of mine last night.
Thanks for the help.

1$ hosting profesionalstore.com

hmm great



Verify your Comment

Previewing your Comment

This is only a preview. Your comment has not yet been posted.

Your comment could not be posted. Error type:
Your comment has been posted. Post another comment

The letters and numbers you entered did not match the image. Please try again.

As a final step before posting your comment, enter the letters and numbers you see in the image below. This prevents automated programs from posting comments.

Having trouble reading this image? View an alternate.


Post a comment

Your Information

(Name and email address are required. Email address will not be displayed with the comment.)

February 2013

Sun Mon Tue Wed Thu Fri Sat
          1 2
3 4 5 6 7 8 9
10 11 12 13 14 15 16
17 18 19 20 21 22 23
24 25 26 27 28