Hi; Ive just built my 3x3x3 LED cubebut I used transistors for each layer AND each cube.
If I activate ONE column and ALL layers three LEDs will light and at 15mA that would be 45mA total, which cant be handled by an Arduino pin; right?
Now I´d like to build an 5x5x5 cube and I found a schematic which uses 74138 chips.
Only the layers use transistors and the 74138 datasheet states 8mA.
With one column lit, thats 5 LEDs. I don´t think this can work; Am I missing something?
the 74138 datasheet
I don't think you can get these nowadays. Do you perhaps mean a 74LS138 or a 74HC138? These have different output current capacities. But yes these sort of chips are meant to drive other logic chips not a bunch of LEDs. You have to use drivers for this. Do you need to source current or sink it with your design?
Thanks,Mike.You wont believe that where I,m from I can,t get a shift register, an LCD Display,almost nothing.Fortunately I used to buy more than I needed a LONG time ago so I still have a few.
But I came across Icky_Unicorns 5x5x5 LED cube and she only had transistors on the layers. I was ALMOST sure that transistors were necessary but sometimes people ( LIKE ME ) make stupid mistakes trying to save a few bucks ( which is an OBLIGATION here ). Im more comfortable with positive logic, so I`m using NPN transistors to drive both LAYERs and COLUMNs
So, it is mandatory to use transistors,right?
But I came across Icky_Unicorn`s 5x5x5 LED cube
Yes but that is an instructables, and as a rule they are crap. This is no exception, we had it a month or two back. Those transistors are all wrong, all the collectors are connected to ground!!! With such a basic mistake you can't trust the rest of the circuit. No doubt she made something but it is not documented correctly.
So, it is mandatory to use transistors,right?
Well no you can use drivers, there are top switches and current sinks available but it sounds like you have trouble getting most things so it is best looking for a design that uses what you can get the parts for.
Well I know enough electronics so I used transistors. Ill try to get ULN2803 though; they make the circuit and layout a breeze. Thanks.
Ill try to get ULN2803 though
Fine but they are only current sinks, that is you can not source current from them.
I cannot believe the degree of gratuitous head-banging that goes on here in respect of LED cubes of 4 by 4 by 4 (single colour) or less!
The obvious and only really sensible approach is to use a single MAX7219.
Two capacitors, one resistor, no transistors.
Possibly built using one of the cheap 8 by 8 matrix boards (kit form) as a base, wires into the matrix pin holes.
Hmmm.