can i build an led cube and to control it with raspberry

Question

Hell o im wondering if is there any possibility to use raspberry as a controller for the led cube ?

magnus2112 · Answer

Yes thats possible! i recommend that you try searching for "how to controll a 8x8 led matrix" It works the same way, just that a led cube is 3d so you wil have to add another script for it to work. Remember the arduino and the raspberry pi is weary like, so you can follow tutorials for the arduino and get the same results, all you need to do is transelate the code to python. If you need help with the code, just ask me

Robert Peter Oakes · Answer

for smooth operation though i'm not sure if the PI will be up to the task, having it as a master and sending the pattern requests to the Arduino is good. I have not yet seen a PI do this. Not saying it cant be done but to be honest, a PI is not the best choice for hardware control of this nature. An Arduino or similar (MSP430, TivaC etc) is much more adept.

Robert Peter Oakes · Answer

Like this http://jacksonliam.blogspot.ca/2012/06/arduino-and-raspberry-pi-talking-over.html Peter

Robert Peter Oakes · Answer

better link here with reasons http://www.raspberrypi.org/forums/viewtopic.php?f=38&t=10120

kidiccurus · Answer

Or just skip the pi and go straight to 'duino.

michaelkellett · Answer

To make a decent LED cube you need to get away from weedy little processors or RP with it's lack of IO and poor real time perfromance. This guy shows you how do it right http://www.hownottoengineer.com/projects/rgb-led-cube.html (And lot's of good explanation.) If I were doing it I would use an FPGA (which would get rid of the LED driver chips) but that's because I use them all the time so I have all the tools. MK

kidiccurus · Answer

You don't necessarily need a driver chip with an arduino. For a 4x4x6 cube I am working on the only io expansion I am using is a single Johnson counter. This is using an arduino Leonardo.

michaelkellett · Answer

I'd still need some power devices for a big display or abright one but: The Lattice ECP2 in 208 pin TQFP package can do a maximum average IO current of 146 x 8 = 1168mA on 146 pins. You can't use all the pins for LEDs so over, say, the 96 pins of Samuel's cube it can do 12mA per LED continuous, no multiplexing required. MK

Robert Peter Oakes · Answer

can the FPGA handle the overall power dissipation, there is always a current per pin but also a total current per silicon chip with most often is not the sum of all or even most of the pins btw, typical LEDs require 20mA for full intensity, as you are multiplexing the pins (There not on continually ) then this current needs to go up proportionately, so if your at a 50% duty cycle, you need 40mA, 25%=80mA etc if you don't account for this then the typical result is un even brightness as the number of LEDs change over the pattern or they are quite dim all the time. just look at how a 7segment display works. yes you can get away with it to a certain extent (Small number of leds ) but it will bite you as your cube grows in size

rew · Answer

Peter, Your concern about the total current (might be per VCC pin or per package) is valid. But about the current: I've built several "multiplexing" led projects over the last few years. Because of the risk of blowing up the leds should the software fail, I always build my prototype with the currentlimit set "below 20mA", intending to up the current when I'm done.... I always end up with: "this looks just great like this, no need to increase the current!". Leds, these days, are simply bright enough at 1/8 multiplexing.... I don't understand what you're saying about the brightness being uneven. If you put the current-limit-resistors in the right place, you'll be driving a column (A plane in the cube) with a power-transistor, and you have all diodes in this plane connected to a driver/one of the FPGA pins through a resistor. Michael was saying he wouldn't use a shift-register to drive the row-lines, because he can easily find 64 (for 8x8) or 81 (for 9x9) row-lines on his FPGA. Nobody is saying you can get around those. Nobody should put current-limit resistors in the column drivers, as that creates brightness differences depending on the number of leds.

johnbeetem · Answer

When driving a lot of current with FPGA pins, you also may need to check the simultaneous switching specs. If you switch many high-current pins at the same time, you can get ground bounce which can affect the signals on other pins in the same bank. You can eliminate ground bounce in software by staggering when LEDs are switched on and off. When I'm driving an LED matrix, I like to use external transistors for each column. That gives me lots of current without worrying about ground bounce and moves power dissipation away from the FPGA.

megabug · Answer

i just made a led cube 8x8x8 controlled by raspberry, I made a interfase with 4 MCP23017 to drive a layer (x,y) and another MCP to control Z

the advantaje is those MCP's can comunicate with raspberry using I2C protocol,

in this moment only i can made figures when only i layer and moving the same figure on the rest of layers, but i can no make any figure that involve two layers or more, i think that i need to create subroutines to made it but i dont know how

any ideas?

michaelkellett · Answer

The nice thing about the FPGA is athat we are working within it's ratings. Lattice spec. the max current per io bank as 8mA * n where n is the total number of pins. The pins are drive controlled with a max setting of 20mA so we are safe with setting a current of 12mA (because we will use less than n pins per bank for LEDs). There is no multiplexing so we can control the current with 1 resistor per LED. The total power disipation in the FPGA IO would be < 400mV * 1.168 A = 467mW. I'm almost tempted to try it ! MK