Lightuino + Ethernet Shield

[Maw]

Hi Andrew

I'm trying to use the Arduino with the ethernet shield, now I can
control a LED matrix from my iPhone. But something is wrong.

I'm have no problem with the code but with electric. I'm using
external power supply about 12V 2A because the amount of LEDs that I
will use. But some resistors, capacitors, and the 5V regulator down
from LM317 are getting really hot and the lightuino stops working.

If I want turn on all the 1120 LEDs, what must be the right power
suply for this?

Thanks

[G. Andrew Stone]

Hi Mauricio,

The spx2954 regulator is rated to 125C and with a 12v input I have seen it get up to 100C when driving the Lightuino's "Arduino" IOs.  So it will feel pretty hot and still work fine!  However, it is possible that it is going into thermal shutdown.  If so, I'd guess that you are driving your LEDs off of it rather then using the LM317 to drive your LEDs.

But basically, you can run the Lightuino with any voltage from 5v->12v.  Using a 5v supply will significantly reduce the heat dissipated by the spx2954.  And to save energy and reduce heat dissipation, its best to pick a value 1volt above the forward voltage drop of the LEDs (for example 12v is a good choice if you are running 3 LEDs in series on each Lightuino pin).  But you are probably using just one LED.  So it would be best to use a 5v power supply.  At 20mA per LED, for all 70 LEDs that can be simultaneously lit you need a 1.5A supply.

Also, if you are using 12v LEDs, you can use 2 power supplies.  Just connect their grounds together in a separate wire and then you can use your 12v supply to drive your LEDs and your 5+v supply can feed into the Lightuino.

Cheers!
Andrew