Think I had posted this in the worg place earlier.
With the help of elders here I managed to finish my 4x4x4 bi-colored cube using a 328 and 4x '595s. I now plan to build a single color 8x8x8 cube using a similar setup with 8 daisy chained '595s. My set up would be
8x8x8 cube split into 64 columns and 8 layers. LEDs would be 2.5v, 20ma
Columns will be driven by 8 daisy chained '595s driving 64 discreet PNP transistors wired high side switches. I will drive these using SPI
8 ground switching N Chanel MOSFETS/Transistors
Since I am using a multiplexed setup max current being switched at any point it 20ma x 64 = 1.28amp. I have a 5v 3amp switching that I bought online
My questions apart from critiques on the general thought process, is on the viability of using an N channel MOSFET such as one of these (depending on availability):
IR540N
IRL2203N
RFP3060NLE
FQP30N06L
for my setup. Would I be better off using a transistor such as the TIP122 or should I go the MOSFET way. I understand that the basic hardware set up is the least of the worries while making a cube, the true challenge is to come up with interesting patterns, but I will request for suggestions on that front once I have the basin hardware down.
So you want to compare MOSFETs. I think you will have to do this yourself by looking at the datasheets and looking at critical parameters like response time, maximum current, and source-drain resistance. I believe MOSFETs do not have a voltage drop like transistors do since the current does not pass a PN junction like it does in a BJT, but I could be wrong. That's how I would get started if I was making an LED cube.
I have a board, see my signature link, that I think would be great for this. It has 12 open drain shift registers. You would need to add 8 P-channel MOSFETs with gate pullup resistors, and 64 column resistors for current limiting.
To run it, you would send 9 bytes of data via SPI.transfer for every layer, update it at a decent rate so it doesn't flicker.
8 of the shift resistors would pull the individual cathodes low to allow them to turn on.
The 9th shift register woud be used to walk a 0 across the 8 p-channel MOSFET gates to turn on 1 layer of anodes at a time.
There are 96 outputs, so you could make a 9x9x9 array (81 columns, 9 layers) if you wanted as well.
81 LEDs on at once could be 1.62A (81 x 20mA if you went for full brightness) so 9 decent P-channel MOSFETs would be needed.
1.28A for 64 LEDs.
@CrossRoads that board does look awesome, although i have slightly different set up. I will be using the LEDs in common-cathode-per-layer configuration. So my columns are anodes driven by the 595's through discreet PNP transistors. I guess the reason I with this approach (for my previous 4x4x4 bi-colored cube) was to save money. Hi-power shift registers are fairly expensive in this part of the world and difficult to find. Shipping to India would be a bummer from digikey or the likes I guess. And honestly i do this purely out of recreational purposes :).
Also, I wish to now get started on doing some home PCB etching. Just that I am too scared to get started on Eagle / KiCad. I have downloaded both but just dont know where to begin. Work has been hectic too. Would be great if you could shed some light on how to go about getting some insight into setting up PCB layouts etc.
"So my columns are anodes driven by the 595's through discreet PNP transistors."
So you have 64 PNP transistors? And then 8 NPN transistors to enable the 8 layers? With 9 shift registers?
Sparkfun has a series of tutorials on using Eagle, I would start there.
In the end it comes down to having good component placement. Without that, routing becomes a nightmare with vias all over the place trying to have signals crossing over each other.
Yup...that's the idea...either 9 shift registers or 8 shift registers and 8 NPNs directly driven from 8 IO pins....although the more i think of it the more i am concerned that more than the h/w it’s the s/w that is going to wreck havoc for me.
See, the way I did the code for my 4x4x4 bi-colored cube was I stored the pattern in PROGMEM as 4-byte values for each layer essentially each bit representing one LED in green or red. There were 4 such sets for each of the 4 layers and shifting them out with 4 SPI commands. I had adapted a fairly popular code that I found on the internet to be able to do this with a lot of help from PaulS. But now having spent time to write patterns for that cube I can very well see that I am in for real big trouble. I would need 8-bytes per layer if I use this approach. It’s going to be a nightmare to come up with pattern and not pull my hair out.
I wonder if there is another way to do this. I am sure you guys must have a better and a more creative solution for this. Would be grateful for any ideas. I also have in inkling to try to integrate an audio input into the cube and make a select switch that allows me to run the cube either off an audio input or pre stored patterns. I was going through Jeremy Blum's arduino tutorials and came across this:
where he use a non inverting op amp to drive an RBG led strip. Do you think it might be possible to adapt this to serve the purpose of an audio input?
Apologies for the longish post. Just that I am really excited to do this project but I want to think this through before beginning.
Much appreciate any suggestions.
nitinarora:
My questions apart from critiques on the general thought process, is on the viability of using an N channel MOSFET such as one of these (depending on availability):
IR540N
IRL2203N
RFP3060NLE
FQP30N06L
for my setup. Would I be better off using a transistor such as the TIP122 or should I go the MOSFET way.
Don't use TIP122 or any other darlington, they have high voltage drop which depends to some extent on the current you are passing through them. As a result, you may have difficulty getting enough voltage to drive the LEDs, and the brightness may reduce as you turn on more LEDs in that layer.
The IR540 is not suitable, it is designed for 10v gate drive, not 5v. IRL2203 is suitable. RFP3060 I can't find, maybe you mistyped the part number. FQP30N06L is also suitable.