SparkFun Forums

[sofiadragon1979]

I am trying to find out if I can wire up an LED matrix (size doesn't matter) & run all the anode pins & all the cathode pins as if it was one LED, so I can make a large blinker. Or will I have to wire all of them up & program as a typical LED matrix.

[Kamiquasi]

I am trying to find out if I can wire up an LED matrix (size doesn't matter) & run all the anode pins & all the cathode pins as if it was one LED, so I can make a large blinker.

You can, just keep in mind that it's fairly inefficient - electrically and practically.

Electrically, let's say there's 20mA per LED. Since all the LEDs would effectively be wired in parallel, a simple 8x8 matrix would give 64 * 20mA = 1.28A. You'll certainly need transistors or driver ICs that can source/sink the required current and leave your Arduino to just do any toggling.

Practically, if you want a large blinker, why not just get one or more bright LEDs (the matrix LEDs tend to be fairly weak) and put them behind a diffusing sheet, similar to SFE's giant wall clock construction?

Which leads to the usual question: what are you actually trying to make?

( Just as a side note.. yes, if you did hook it up as a usual individually-addressable LED matrix, you could still make the whole thing blink on and off.. it would just be dimmer than usual due to the required sequential addressing of rows / columns, but your eyes should still be fooled into thinking it's blinking on/off as a whole. )

[elevator4]

Hi,
You can always try but to somewhat level out the differences in Vf I would at least use (for an 8x8 matrix) 8 resistors at the cathodes and 8 at the anodes, then tie all the cathode R's together, same for the Anode's. Calculate the Rs to provide current for 8 parallel LEDs each (eg 20mA*8=160mA. That's a lot of current for the whole matrix BTW (1.28A total).
An easier approach to a big blinker: A power LED with a diffuser film in front (eg http://www.optigrafix.com/light_diffuser_film.htm)
-E
PS I see Kamiquasi just answered along the same lines...

[sofiadragon1979]

I am trying to make a very noticable turnsignal for a HPV that I am designing, & I was curious about this idea & I was getting frustrated that I couldn't find anything about it. I thank the both of you for your help, you have given me answers that I needed & now I will look into other ideas.

[MaJiG]

You have two good answers already.

I would just add that LEDs in parallel need to each have it's own current limiting resistor. The voltage drop of an LED varies from device to device and also varies according to the current driving it. If you place several LEDs in parallel, one or two (the ones with the lowest ON voltage) might light and the others stay OFF. This is because once the lowest voltage LEDs turn ON the voltage will never go higher to turn ON the other LEDs.

By giving each LED its own current limiting resistor, you allow each LED to come ON and the resistor drops the remaining voltage. Thus, each LED can have its own individual ON voltage irregardless of the other LED's ON voltage.

This was implied in the other (excellent) answers, but I just thought I'd point it out.