Saturday, October 16, 2010

LED Matrix 101

As a dummy in electronics I still find somewhat difficult to understand most electrical schematics and what parts to use on my projects.

My first attempt to do something more elaborate than to burn LEDs directly on a battery was to understand how does a LED matrix work.

I've read about 'multiplexing' and 'persistence of vision' but how does it work and how can i build it?

Looking at the schematics it would seem that all the wires are connected, but you should connect all the positive ends (anodes) to form lines and the negative ends (cathodes) to form columns separately.
As it is something hard to breadboard, it's best to really solder it all (if you want to breadboard it anyway take a look at this).

My doubts were what resistances to use and how to calculate them for such a complex schematic. Well, after some thought, I realized it's not complicated.

What we do to light up a LED matrix is to light each LED individually at a time. We only do it so fast that our eyes won't notice.

So, we only need to take that single LED into account when doing the math. There's no serial this or parallel that to complicate as it would appear initially to the untrained eye. At any given point in time we are dealing with such a simple circuit as this:

I know that my blue LEDs consume about 4.5V on a 30mA current (as stated in here), so, to a 9V battery i should use a 150 Ohm resistance [V=R.I ==> R=(9-4.5)/0.03=150].
The closest value resistances I have are 220 Ohm, so I'll use those.

I didn't have a perforated board on me and couldn't buy one in time so i turned to a Pringles pack lid for a 'solid' base.

With a matrix designed in a piece of paper where to perforate and fit the LEDs, we get an interesting place to solder our LEDs.

This is the end result:

So what now? The next step shall be to connect it to the Arduino and make some letters appear on my home made LED matrix.

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