Requesting help w/ RPi Project.

Hi, Peter

You may use a RPI accessories ———embedded pi to do it,see more in http://www.coocox.org/epi.html and http://www.coocox.org/blog/

Best Regards

Sam

Hi Peter - you may want to check out the PiRack which has only just come out - theres some more info about ithere : http://www.element14.com/community/videos/9289/l/pirack-introduction-video--piface-expansion-board-for-raspberry-pi

The RPi has 17 available IO pins. So driving 64 panels is going to be a challenge.

You could arrange them in an 8x8 matrix, but there is another potential problem. The amount of current you can draw from the IO pins of a Raspberry Pi is very limited, you may not be able drive 64 panels.

We need more information:

- What kind of light source are you going to use?

- How large/bright do these panels need to be?

- Are they each going to be a single colour or do you need them to change colour?

- Do you just want to turn them on and off or do you want to control the brightness?

- How far from the RPi will they be mounted?

- Is there any thing else the application needs to do beyond control the lights? 

If you want advice on any of the above that's fine, but some of these I suspect are already fixed by what you want to do.

- Derek

Derek Campbell wrote:

 

The RPi has 17 available IO pins. So driving 64 panels is going to be a challenge.

Look up the Microchip GPIO Expanders MCP23017 / MCP23S17, these are 16bit expanders and you can daisy chain 8 of them per i2c bus or SPI chip select. By my count that lets you have 256 IO pins using just 5 on the Pi.

As with any GPIO expanders, you're going to be limited in some way on the frequency you can update them, but as Peter didn't specify what his lights are we have no way of knowing if that's a problem.  Simple number of GPIO pins isn't a problem.

The lights in the panels are regular LED-Tubes, like one might find as a Christmas decoration. They should be individually controllable, and some kind of brightness control would be nice, but not necessary. The panels will be used as regular room lighting.

@selsinork: Yes, that is a possibility, but depending on exactly what Peter wants to do, that may not be the cheapest or best solution.

I did not want to be recommending IO expansion without knowing the requirements.

Let's see what he needs to do. :-)

Peter,

So you mean like a skein of LEDs in series? Do you know how many LED's are to be controllable together?

It sounds like you will definitely need some kind of I/O expansion, even if it is just current drivers. You can't draw that much current from the Pi GPIO.

best,

Derek

I'm not planning to pull all the current from the GPIO, i'm will be using transistors to amplify the current. I just need it for the on/off.

Yup, that'll work. Just checking, not everyone appreciates the current draw limitations of the Pi.

If you don't need maximum output, you could consider multiplexing them, but I think Selsinork's suggestion will give you the maximum flexibility with respect to adding brightness control later.

Those expanders are pretty low cost and four will cover your needs.

Derek Campbell wrote:

I did not want to be recommending IO expansion without knowing the requirements.

Well, as you observed, 64 into 17 doesn't go, so one way or another you're talking about expanding the number of outputs.  Beyond that is up to Peter.   Cheapest and 'best' don't necessarily end up being the same,  'best' may end up being not to use an RPi, but choose something more appropriate to the task ?