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LED displays, counters, ad signs

Picture of LED displays, counters, ad signs
These are two older projects of mine, I found the design files in some older folders while looking for images for another instructable I was making. I will present two projects, showing the steps that need to be done by those who wish to make something similar.

I've only had two main LED projects during the years, one was a LED ad sign meant to bring attention to an arcade game bar, the other was a simple counter that had to be big enough to be seen from around 50 meters.

The projects were easy to build, the arcade game sign got place on perfboard, I haven't bothered to make PCB for every letter plus mainboard. Shaping the letters is at the choice of the builder, just take care to allow the same amount of current through each LED segment, to have the same brightness everywhere.

Let's move on to the first project, the arcade sign board!
 
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Step 1: Building letters out of LED-s

Picture of Building letters out of LED-s
ledschem.GIF
Being the simplest thing of all we have to do, let's start with the mechanics part. Back then I didn't had the CNC mill, so cutting an enclosure for this project was a task to be done by hand. 
I made a 5 x 7 hole matrix on a perfboard with 3 millimeter holes, to be my stencil when drilling the holes for the letter LED-s. I put that on the cable cover, and drilled out holes in a way to shape out the letters I needed. The text i needed to drill out was:
"JOCURI ELECTRONICE". I drew the letters on paper first, to make sure I get them right. Unfortunately I haven't made any pictures of the enclosure, so I can't show you building details.
For 5 mm LED-s you should drill 5.5 mm holes, otherwise, they're not going to fit in.
When you're all done with the enclosure, paint it, if you want, I sprayed mine with black spraypaint.

When the enclosure was done, I started to work on the letters. I pushed them down so they touched the board, and soldered them on bottom side. When you're done with that too, cut down the pins at the solder joint, and put away the pieces. Led pin excess wires are a good thing, don't throw them out, you can use them later as pad-to-pad jumper wires. We are using them to connect our LED-s in series, too.

To have the current consumption at a minimum, you'll have to think of connecting them in series. This way, the same 20mA flows through each one, lighting them all up. I had a power supply of 12 volts available, I decided to use that for this project. With a diode forward voltage of 2 volts, that gives me a maximum of 6 LED-s that can be tied in series.

Let's see some calculations for a few letters:

Letter J - 11 LED-s in total, I split them in a 5 and a 6 LED group. These LED-s have their forward voltage somewhere around 2 volts, so I didn't use current limiting resistor on that group. The 5 LED group instead has a total voltage drop of only 10V.
Let's see a resistor value for this group:
R = ( 12V - 10V) / 0.02mA = 100 ohms. This is even a common value to find in stores.

Letter O - can be split into 2 groups of 5 LED-s and a group of 6 LED-s.

Letter C - I split that into two 4 LED groups, and a 5 LED group. The resistor you need for a 4 LED group is:
R = ( 12V - 8V ) / 0.02 mA = 200 ohms

Letter U - can be split into 3 groups of 5 LED-s, you'll need to add a 100 ohm resistor at each group.

And so on, for all the letters you need.
Then, they must be connected to ground, and power supply. Since we must give a possibility to turn them off and on, we need to add a switching element. I added a bipolar transistor on the high-side. Please refer to the simple schematic from the photos to see how they have to be connected.

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