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Can/should the raspi control 100+ LEDs?

Posted: Thu Oct 31, 2013 7:46 am
by pukster
I just ordered 50 LEDs and I want to begin experimenting with them on the raspi (specifically boblights). I imagine it is pretty straight forward to do so, as you connect two pins from the LED strip to the GPIO pins of the raspi (as per these instructions) and then presumably control them via software. Now, what about if I have two TVs, each with their own led strips (for the moment assume the same RGB patterns sent to both strips), will the raspi still work? What about 4 TVs? 16? 32?

Obviously I won't have 32 TVs, but I am looking to put LED lights all around my house (living room, bathroom, bedroom, hallways, office...) and I want them all to be synchronized and linked to whatever media is playing (be it audio and/or video). I can carry out the synchronization via MPI as I am familiar with that, but can the raspi physically handle that many connections (>100 individual led groups)? If so, how? If not, what are my options?

Thanks

Re: Can/should the raspi control 100+ LEDs?

Posted: Thu Oct 31, 2013 11:36 am
by BerryPicker
The data and timing lines of LED strips present an insignificant load to the Pi so you should be OK adding more.
www.youtube.com/watch?v=R-0Beb7i7Sk

Re: Can/should the raspi control 100+ LEDs?

Posted: Thu Oct 31, 2013 12:17 pm
by texy
Just make sure you have adequate power to cover them - obviously not directly from the Pi ;)

Texy

Re: Can/should the raspi control 100+ LEDs?

Posted: Thu Oct 31, 2013 6:01 pm
by pukster
texy wrote:Just make sure you have adequate power to cover them - obviously not directly from the Pi ;)

Texy
I guess my question is how do I connect it all to the raspi? Do I use a solid state relay? I mean there are only so many pins on the Raspi and due to distances it might be impractical for me to connect all the leds and led strips in a circuit (ie. Raspi out to kitchen led, out to bathroom led, out to living room led1 to living room led2...all the way to the last hallway led.

I definitely don't expect people here to do all the work, but a few links or terms would go a long way to help me. Thanks

Re: Can/should the raspi control 100+ LEDs?

Posted: Thu Oct 31, 2013 6:26 pm
by karlkiste
If all the LEDs should do the same, you don't need a GPIO pin for each strip. You can just use buffers, which send the same signal from one GPIO pin to all the strips.

I'm currently working on a project where one pi will control about 3500 LEDs, each individually, through one pin ;-) But that's another type of use.

Re: Can/should the raspi control 100+ LEDs?

Posted: Thu Oct 31, 2013 6:59 pm
by pukster
karlkiste wrote:If all the LEDs should do the same, you don't need a GPIO pin for each strip. You can just use buffers, which send the same signal from one GPIO pin to all the strips.

I'm currently working on a project where one pi will control about 3500 LEDs, each individually, through one pin ;-) But that's another type of use.
Well not all of them will do the same thing. I want to be able to dim the Kitchen when watching TV (btw can the raspi dim LEDs?) but still have boblights behind the TV(s) and match the infinity mirrors to the TV. Alternatively, during a party I might want the TV to display visualizations/photos with boblights corresponding to those visualizations, and have the rest of the LEDs synchronized to some music. I will deal with the synchronization, but I need to know where to start researching the hardware side.

For example, this 'buffer' you refer to, what is that? A search for 'raspi buffer' does not return what I am looking for.

Re: Can/should the raspi control 100+ LEDs?

Posted: Thu Oct 31, 2013 7:16 pm
by karlkiste
A buffer is simply a buffer, nothing raspi-specific. I use a 74HCT245 to shift the 3V3 output level to 5V and make eight outputs follow one GPIO pin.

The raspi cannot dim LEDs, the WS2801-LEDs used for the boblight have a dimming circuit built-in. This circuit can be controlled by the pi.

Re: Can/should the raspi control 100+ LEDs?

Posted: Thu Oct 31, 2013 7:27 pm
by pukster
Dimmable is generally not a term used when describing LEDs (actually, I suspect it's not a word at all). This is the only one I found that claims to be dimmable.


TaoTronics

It's actually a good deal...sold!

Re: Can/should the raspi control 100+ LEDs?

Posted: Thu Oct 31, 2013 8:14 pm
by karlkiste
That strip is not good for the boblight thing. It can change color, but the whole strip has always only one color. With the WS2801-type LEDs, each LED can have its own color.

Re: Can/should the raspi control 100+ LEDs?

Posted: Thu Oct 31, 2013 9:31 pm
by pukster
I didn't actually buy it as it got negative reviews about the smell. The problem with the WS2801 is that they don't dim. How do I manually dim LEDs?

Re: Can/should the raspi control 100+ LEDs?

Posted: Fri Nov 01, 2013 12:52 pm
by klricks
pukster wrote:I didn't actually buy it as it got negative reviews about the smell. The problem with the WS2801 is that they don't dim. How do I manually dim LEDs?
You can dim with the WS801 by varying the PWM. (Pulse Width Modulation or vary the ON vs OFF time).
See the data sheet:
http://www.adafruit.com/datasheets/WS2801.pdf
Also find the typical circuit diagrams in the data sheet.

The only other ways to dim LED's is to drop the voltage or increase the dropping resistor(s).

Re: Can/should the raspi control 100+ LEDs?

Posted: Fri Nov 01, 2013 6:10 pm
by Mattylad
My son got a set of lights, looks exactly the same deal as the above Amazon link but it was only £12 ish.

Re: Can/should the raspi control 100+ LEDs?

Posted: Fri Nov 01, 2013 8:01 pm
by FLYFISH TECHNOLOGIES
klricks wrote:The only other ways to dim LED's is to drop the voltage or increase the dropping resistor(s).
I would never dim LEDs by decreasing the voltage accross them or by increasing the resistor.

However, next to (preferred) PWM control, there is additional option to control brightness - by changing the current.
At first sight, changing the current seems equal to changing the voltage, but it is not...

LEDs have non-linear characteristics. Even the same model have slight discrepancy, what means that at some small voltage one LED would already lit, where the other would not. Moreover, this is very common for various colors...


Best regards, Ivan Zilic.