Friday, March 4, 2011

Project 19 - LED dot Matrix Display - Part 1

I'm quickly learning that when you work with electronics it's best to do so when your frustration level is low...

Thankfully, when I opened up my new box of goodies from SparkFun (who, once again, managed to package 10 items in a 4"x5" box - love it), I was in a good mood. Here's what happened from there...

First, I found the data sheet for my 8x8 Dot Matrix Display (C+) - feel free to take a look at it here. I'm including a few screen caps here of the data sheet to show you that the pin layout matches exactly the one that the author provides on page 132 in Figure 7-2. Woo Hoo... I won't have to worry about modifying the code due to pin differences.

Next, the data sheet was very clear on how to find pins 1-8 and 9-16... the small display has two notches that are raised and two notches that are recessed. If you turn the display so that the two raised notches are on the S and W edges, pins 1-8 are on bottom and 9-16 are on top.

Once I figured that out, that's when I hit the bump in the road... as you can see from one of my photos here, when you insert the display on the breadboard, the pins are inserted at the topmost set of pin holes and the bottom-most set of pin holes, leaving no holes for jumper wires. Figure 130 shows the display with two rows of free pins below the display and one row of free pins above the display... and that's my problem. Not sure if the author actually had an 8x8 display that didn't come in a shell like mine or if the display found in the program, Fritzing, doesn't take the shell into account when it comes to proper spacing... either way, I'm unable to wire up Project 19 until I find a work around...

One option is to solder some longer wires to each of the pins on the display and then I can insert these and leave the display free-floating off of the breadboard.

Another option I'm considering is using headers (I have a bunch from the Make: Electronics book project) and solder wires onto those - this would save my display's pins and leave them unaltered.

Thoughts from my readers? Any other suggestions?


  1. The pins are going to go into rows B and I of your breadboard. The jumper wires are going to have to go in rows C, D, or E and rows F, G, or H. and then be routed out from under the display is the same size as yours and I saw the same problem.

    I thought about rigging up a breakout board, but decided to just buy another small breadboard for this instead.

    I'm going to use some spare ethernet cable for the jumpers because it will give me a color coded lead for each pin on the display.

    You are passing me now, I am still playing with the binary counter circuit and trying to figure out a bit more about running the 595 shift register. They cylon eyes trick has me stymied...mostly because I can't seem to come up with a block of time to just sit and study on it.



  2. Routing the wires underneath the display doesn't seem like a good idea - seems like it'd be too easy to have a wire that doesn't make a good contact or comes loose. Maybe I'll try it - beats soldering, but then again I need the practice.

  3. You could do something a bit like this:
    Rather than using headers you could solder up some wire instead personally though I think I'd just stick the wire underneath, however I have a breadboard allowing me to wire it up with wires out the side, I took some picks and uploaded them -

    Hope those help, I look forward to the rest of your projects,
    Keep up the good work

  4. Hi, Will - thanks for sharing. That's another option I hadn't considered!

  5. Also, just in case you haven't already seen it,
    MAKE's circuit skills this week was on LED matrices

  6. Dear fellows: I studied electronics 45 years ago, graduated in Computer Science and then went to Law School, that's how I make my living today. But I never gave up electronics and music for they are very relaxing passtimes. So I bought an Arduino kit and this book, and came across the same problems: lack of parts, different parts, but Jim's site is very cool and shows very good practice information. Now I'm getting momentum again. This is particularly very helpful idea. How come good ideas take time to figure out? Thanks to dewo I am using two mini boards for this project and it is working fine. Thanks again Jim, dewo and other collaborators and greetings from Brazil.