Step 4: Installing the Diodes

You will be fashioning pins to be inserted directly into the MPC board. Make VERY sure that you are able to attach them directly into female headers (sockets) labelled D12 to D8 on the microcomputer board. The larger MPC boards have a gap between pins D7 and D8; make the necessary adjustments to your installation!

Bend the leads of 5 x 1N4148 diodes to come out the the space at the bottom, with the cathode (-), banded side pointing towards the LEDs. The anode (+) end will attach to the micro's pins. If you find the wires too flimsy as a connector, reinforce them with a heavier wire.

Attach the cathode ends by thin wires to the LED's anode (row) ends: pin 12, row 1; pin 11, row 2; pin 10, row 3; pin 09, row 4 & pin 08, row 5.

<p>Here is the image of the LED board shown in Step 5 with a bit more description. The resistors are hidden by Layer 2 but the green lines show where they connect.</p>
Hello. I just noticed that your pictures don't match the description. In a picture row 1 connects to arduino pin 8, row 2 connects to arduino pin 9 and so on. In description row 1 connects to arduino pin 12,.... So I would just like to know which one is correct? Keep up the good work!
hello nice 'ible! do you by any chance have code for the scrolling text? that would be wonderful
the fact that you need to already own a $30-$50 device pretty much ruins the "low cost" part. but good guide for those that have an ardunio already.
One can make Arduino at home, for lets say $10-$15. And when student (or someone else with really tight budget) gets Arduino for $30-$50, it's good to be able to get cheap accessories for it. This is one of those "why I didn't thought that" -moments. Great instructable!
Actually, I just re-ordered the BOM for a really barebones arduino-compatible I build on perfboard, and the final cost per board is only about $7. Granted it lacks built in usb (I make versions with RS232 for a few bucks more) and a 5v voltage regulator would add a little to the price as well. That's besides the point, which is that getting a device to run this display isn't something that will require a hefty hit on the wallet. If you've got cash to burn, you should concider some of the nicer boards like the official Arduino or it's clones. They definitely add a whole new degree of usability and comfort.<br /> <br /> On a completely different subject: With fairly minor modifications (wiring and orientation of the leds) the same display could be charlieplexed, allowing for it to be run from a mere 5 pins (unless my math is off). Charlieplexing can be daunting when beginning electronics(who I'm assuming this instructable is mostly aimed for), but with a bit of planning and good notes of the wiring it can be a great way to multiplex leds for projects just like this.<br /> <br /> Anyways, great instructable. Really informative and detailed and easy to follow. And A+ on the pictures, they're all well focused and framed to show the &quot;good bits&quot; :)<br />
So went and build this matrix and everything seems to work. But I did it without the diodes. I just soldered a resistor on every row (+) and the scanning works great. Also I tried the VU meter code from part2 and that too seems to work. So my question of course is... What's with the diodes? O and thank for the tutorial ofcourse, it's my first "big" arduino project.
The diodes are there because the uP will operate the LEDs at their maximum reverse limit of 5-volts, and COULD damage cheaper LEDs.
Ah I see. Well I don't think I used "cheaper" LEDs but we'll see how long it holds out. Thank you and I'll be looking forward to the scrolling text instructable.
O and another thing. Have you posted more code elsewhere besides the "vu-meter" and test lines? I absolutely NEED more code for this. Thanks again!
I'm in the process of putting together another 'ible on scrolling text - should be along as soon as I have the time. qs
I´m trying to put text, but i´m new on programming, do you have a sketch with the scrolling text?
If we upgraded the project, it could be a small commercial system for small businesses. For example, we can use FPGA to replace 4000 logics to drive more LEDs, use a microcontroller (like AVR or PIC16/18) and an SD card slot to allow customer to run custom patterns in the LED panel. <br/><br/><hr/>Electo-Matic<br/>
The LMP can certainly be ramped up to virtually any scale.<br/><br/>I designed this to be a low-cost project (under $10 in parts) that anyone with an Arduino and some electronics experience can build, and many of the special effect features are already designed in. You can see some from this demo video here:<br/><div style="margin-left:15px;"> <object width="425" height="344"><param name="movie" value="http://www.youtube.com/v/lCBOTupvXIY"></param><param name="wmode" value="transparent"></param><embed src="http://www.youtube.com/v/lCBOTupvXIY" type="application/x-shockwave-flash" width="425" height="344" wmode="transparent"></embed></object></div><br/>
what are those blue lights moving up the screen?
They're not really there - probably just refraction from the lens of the video.
This is my favorite:<br/><br/>The <a rel="nofollow" href="http://www.youtube.com/watch?v=QOaRkNicoxI&feature=channel_page">MUSICATOR.</a><br/>
Sorry but I'm new to programming, do you have a sketch of the actual text scroll code that I could learn from.

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