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rgb led cube

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Dr_Doggy

Well-Known Member
i had another thread, but i cant find it, and lots of changes were made anyway but now i seem to be running in to problems,

It started when I used common cathode leds instead of anodes, so now what im doing is simply using uln2003's controlled by shift registers (25 outputs) to close the ground circuit

but at the source(5v) where i control my layers with three uln2003 's controlled by two 74hc238 mux.
but it didnt seem to work so i pulled the uln2003 and ran the layers direct with the mux, which worked better, but not enough current, espically due to the fact that i need to switch between the rgb so 1/3 but also between 5 layers, so its even worse @ 1/15 cycles, my plan is to pump it up a bit using a 497-3110-ND mosfet to switch each layer, after regulating it at 3 - 5 vlots, (and invert my mux output),..\

is this a good idea? is there a better way to control my sourcing?
 
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alec_t

Well-Known Member
Most Helpful Member
Eh? I don't know about other forum members, but I for one haven't the faintest idea what your circuit is supposed to be doing. Can you post a schematic?
 

Dr_Doggy

Well-Known Member
um, best i can say is that it is a LED array driver, 15 x 25 led's, so 15 source channels and 25 sync channels, i lost the schematic and cant find it on web:(
 
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Gobbledok

Active Member
I made a small RGB cube using common cathode LED's but it was a lot easier to use common anode. I eventually made another one (CA) because they are a lot easier to drive and more versatile.

With a common anode I used a TLC5940 to control the LED's and (possibly) the anode transistors.

My cube was only a 4x4x4 RGB though. I used a 1/16 duty cycle; each row of 4 RGB's is scanned in sequence.

You could also use 3 TLC5940's for a 1/4 duty cycle for more brightness. Each level would then be scanned in sequence.
 
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Dr_Doggy

Well-Known Member
i really did mean to get the common anode,, and if i do anything similar i plan to do that,

on the cathode end of the diodes i use the uln2003 to provide ground controlled with shift registers, an that works ok.

the problem is that the multiplex suppling the anode arrays' is only @ 7ma on each output but since the LED layer goes from 20-500ma i need a way to regulate it @ 3v PLUS be able to supply the current

and using the uln2003 doesnt work(@ the anode side)

i guess i am just wondering if the above listed mosfet will work for my purpose to be switched with the multiplex and supply the sufficient current to the anode, (also shouldn't the uln2003 do that? )
 

Gobbledok

Active Member
Whether you regulate to 3v or not, you will have to have a resistor for each anode (color of each LED). For a 4x4x4 cube you will need (4*4*4*3) = 192 resistors.

Then you need a uln2003 output for each row, and a source for each colour.

It really is easier to buy common anode LED's and use TLC5940's though. I bought 100 RGB LED's from eBay with 300(!) resistors for US$25. The TLC5940 has a 16 current limited PWM outputs and can be driven at up to 20MHz and can run at 3.3v.

Anyone want to buy 600 resistors? lol
 
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