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# What size of resistors should I use? Answered

I'm going to build an 8x8x8 LED cube and I am confused about what resistors I should get. Here is a link to the blue LEDs that I bought: http://www.ebay.com/itm/110942426746?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1439.l2649. This step https://www.instructables.com/id/Led-Cube-8x8x8/step14/Choose-your-resistors/ says to use the burst load of the LEDs but the chart on the item page is somewhat confusing to me. I know that with the resistance equation it would be R=3.2v/0.02A but I don't know if that is the right mA. I am pretty new to electronics so any help is appreciated.

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## 4 Replies

icengBest Answer (author)2012-10-31
The LEDs you bought are rated at 20 ma == 0.02 Amps reading the eBay site.
I agree with canucksgirl this is a major project.

As I see it the 5V supply has to overcome
• The 74HC574 IC gate say ( 0.5 forward voltage ) loss
• The LED 3.3 average forward drop
• The resistor then only needs to support
• 5V - 3.3V - 0.5V == 1.2 volts
• and R = 1.2V / 0.02A = 60 ohms
A

canucksgirl (author)2012-10-31

I hope you don't mind me saying so... but I don't think this project is right for you (at least not right now). The author noted in "Step 1: Skills required", that you should have a basic understanding of electronics and recommended against doing this for one of your first projects... I also agree with the author. ANY project that has a total of 72 steps is liable to be more intermediate/advanced; and judging from the enormous amount of comments from confused people, it probably wasn't an easy project for them to do either (if they were ever able to get it done and working)...

What I would suggest you do is start with the basics and get yourself a good understanding of electronics before you try tackling something like this.

There are many good beginner projects here, but I would suggest that you start with this Guide to Basic Electronics. In it, there are several instructables. Start with the one by randofo for Basic Electronics as he does a great job explaining things. There are other topics in the guide like working with a breadboard, soldering, working with a multi-meter, LEDs, Diodes, Motors, Relays, Transistors, Resistors, working with Arduino and more!

Once you have gone through those Instructables and made a few easy projects, you'll be ready to try the LED cube.

Once you've done your first easy project, post a picture for me on my page (if you want) and I'll send you some free pro membership. I've earned quite a bit here, but I'd be willing to help you out. The pro membership will allow you to get PDF files for any project here (which is great for when you are trying to work on a huge project like the LED cube). Then you can get creative and make your own project to share here (and possibly earn yourself more free pro membership). :-)

Arya42 (author)2012-11-01

Maybe you're right. :/ Since I have most of the parts ordered, I'll think I'll look at those instructables you suggested and try a smaller cube. If that goes well I'll try the big cube.

rickharris (author)2012-11-01

Start small and build up your skills and knowledge.

Flash a few LEDs to learn how to control them

see this answer I post a few seconds ago

this project  is a none trivial task for a beginner.

I would start with a single LEd then make a 2 x 2 cube an build up.