since the driver circuit is already setup and done now i am looking for a way to use an external power source but keep it isolated from the arduino. so the driver circuit and arduino itself it powered by the usual way through USB but the LEDs are powered through a separate 5v power supply. how can i do this?
the only way i can think of is to connect outputs of the 595s to PNP transistors which will switch the anode columns of the cube. so 1 transistor per anode column. for cathode layers, we will stick to the earlier method of using NPN transistors.will this work?
is there a better way?
Connect the power supply ground to Arduino ground, use the external supply for the LEDs+595s...and that's it!
Without using more Arduino pins...?
thanks for the answers fungus! a few follow up questions...Quote from: fungus on May 31, 2013, 01:41 pmConnect the power supply ground to Arduino ground, use the external supply for the LEDs+595s...and that's it!i wanted to use the external supply ONLY for the LEDs. you mentioned that i can use it for the 595s as well. will the current through the 595s will not be too much? each 595 might need to switch on 64 LEDs together (i only have 74HC595s, no access to TPICs). hence i thought of powering the 595s off the arduino itself and limit the external power supply to the LEDs only. is my logic wrong? and is this doable?
Quote from: fungus on May 31, 2013, 01:41 pmWithout using more Arduino pins...?no! i am using only 3 pins from the arduino anyway. I am ok with using all the pins on the arduino if required.
Most people power up a layer at a time with MOSFETs then have 64 current sinks in the base (eg. 8x595s) for the LEDs on the layer. Doing less than a complete layer makes the wiring more complicated and the LEDs dimmer due to extra multiplexing.