LED Binary Calculator

Step 3 Schematics

As always the only thing I left out in the schematics are the resistor values which limit the current to the LEDs, this is a thing every one does by himself.

You can use a special site to calculate the resistor value like this one . Or do it yourself with the help of a simple equation (Vin-Vled)/(Iled).

I recommend downloading the original file with the schematics to see them clearer.

Comments

[pilotavery]

Would you sell it? $30?

[Syst3mX]

There is nothing left to sell the project was recycled to something else

[cosmicr]

how come you don't need a resistor per led? they are wired in parallel but there is only one resistor per row?
this article: http://www.kpsec.freeuk.com/components/led.htm#series says it wouldn't work?

also, using 91 ohms and 5v does that mean your led current is 55mA? That seems high to me and using (Vin-Vled)/(Iled) it would mean your led is 0.086V? I'm confused.

But thanks for the great instructable, I'm planning on using these concepts to make a bit led array (as soon as I get my head around it!)

[Syst3mX]

Because I used the same type of LEDs in this project(they all came from a batch of 1000 LEDs) There is little worry for on LED taking all of the current.

If all of the LEDs are the same the current will divide equally between the 3 LEDs.

But the article is correct generally it's not the best of ideas to use just one resistor but I wanted to save some space and I had the same type of LEDs.

[m1s73r]

I've got a question:

So, you're using blue LEDs and resistors with 91ohm... But my question is what's the source voltage? Doesn't the voltage regulator lower it to 5V ? Therefore you should use 120ohm resistors - am I right?

Thanks

[Syst3mX]

Yep you are correct but my cheap ebay LEDs work like crap with a higher resistance.

[m1s73r]

Oh ok, hopefully mine work better... I bought 50 LEDs + 50 resistors for just 6,77 $ But anyways, thanks for answering my question!

[callain]

Is it bad if you replace the 74HC594 by a 74HC795N or a 74HC795D ??
Thanks !

[Syst3mX]

I have never heard about this kinds but the schematic has it a bit wrong the part is : 74HC595

[callain]

So is it ok ?

[Syst3mX]

a 74HC595 is ok the 74HC795 i can't find at all

[Brett_cgb]

I'm surprised you didn't use PD0-3 as the driver to your 4x4 keyboard (drive the columns with PD0-3, read rows as you are now). That would free up 4 pins, and you're still scanning LED columns.

[Syst3mX]

yeah that is a very good idea and to be honest it didn't accrue to me at all. Like they say you live 100 years and you learn 100 years :)

[osgeld]

your schematic is a tad hard to make out once instructables mangles it, might I suggest adding the following link to the full sized version? http://www.instructables.com/files/orig/FYB/GPXO/GD0R15NS/FYBGPXOGD0R15NS.png

[Syst3mX]

hhh yeah the resolution falls dramatically, but i wrote down to download the original file. But adding a link would be a lot better, thanks for your advise.