Best way to control 75 LEDs with Arduino

Question

I need to control 25 groups of 3 LEDs or 25 RGB LEDs. Each group will be dismissed from the uC by up to 20 cm (about 8 inches). 20 cm is very safe assumption but I think it will be 10 cm or less.

However, I think If it be even 5 cm, it will be hard to create in matrix way, so I think using MAX7219 likie IC (http://www.arduino.cc/playground/Main/MAX72XXHardware) is not best idea.

I will probably use shift registers (http://www.arduino.cc/en/Tutorial/ShiftOut). I can connect multiple 74HC595 or use something like STP16C596.

I prefer STP16C596 but they are obsolete. I found SCT2026 (http://zefiryn.tme.pl/dok/a04/sct2026.pdf) but I'm not sure is It right choice.

One more note. My current project requires only "2 bit control" over each group (3 LEDs off, or selected and turned on only one of them), but I don't think it make my project easier or cheaper, also controlling each LED separately will give much more flexibility in case of changes.

What solution will be fit best for my requirements.

It will be nice if parts will be available in this shop - http://www.tme.eu/en/katalog/?&page=1,20#main or http://eu.mouser.com/ (but i prefer first one).

Answer 1

I would suggest going the matrix route with a driver like the MAX7219 you mentioned or maybe, if you wanted a lot more control, the TLC5951DAP, a TI LED driver meant for RGB leds that will give you 24 channels with a 12 bit resolution (4096 different steps of brightness for each channel). This will allow you to turn on each of the R, G, and B LEDs to different brightnesses to mix the colors to what you want.

You could use ribbon cable for the wiring to each of the LEDs (I'm assuming wiring is why you do not like the idea of the matrix) and have all of the cables plug into a controller board. For something like this, I would definitely recommend that you make a pcb for the controller because that's a lot of connections to try to do by hand. That's just what I would do though.

The STC2026 looks to be directly compatible with the STP16C596, so that's a perfectly good replacement if you want to use it. I would agree that controlling each LED individually will probably be cheaper and easier than trying to use some sort of MUX to have 2bits control which LED is on.

Hope that helps.

Answer 2

I don't know of any chips off the top of my head, but perhaps some of those I2C GPIO/output expander chips might be the way to go. It has been a while but I'm sure I saw 4bit ones around. Of course, going this avenue may not be as cheap as some other solutions but it would be easy to expand it in the future and use minimal arduino pins.

Apologies for the lack of detail, I am posting from my phone.

Answer 3

You can use the M5451 chip to economically drive constant-current outputs. My board uses them to directly drive 70 constant-current "sinks", and provides 16 500mA "sources" for people who want to do large LED matrices.

http://www.toastedcircuits.com/html/product/Lightuino_5.0.html

Answer 4

I've used a bank of three TLC5490 chips to do individual control of 16 RGB LEDs. It's used in my RGB LED Shield project. If I were reimplementing it now, I'd use the easier-to-program TLC5497 chip which has 24 output channels, versus the 5490's 16 channels. MaceTech is selling those in small quantities with immediate availability. I'm planning on using one with a FT232R to make a LED USB dongle for the Chumby.

Answer 5

I wrote a library for Arduino to do this with shift registers, it's called ShiftPWM.

You can find detailed documentation here: http://www.elcojacobs.com/shiftpwm

And a schematic for regular LED's here: http://www.elcojacobs.com/using-shiftpwm-to-control-20ma-rgb-leds/

I recommend using a TLC5916 over a 74HC595, which is a shift register with constant current sink outputs. You would not need resistors with this driver.