[PD] connecting Pd to LEDs

[Jim Hickcox]

For the archives, I had emailed my brother in law Pete about the
potential of using an arduino chip to process the midi and send the
signals to the LEDs, and his response was fairly enlightening as well,
so here's that in case it's helpful for the future:


The "analog" outputs of the arduino are in fact pulse width modulated
(PWM) digital signals. These are easy to convert into an analog
voltage with a filter but you dont have to worry about that.
The best way to dim an LED is with PWM. What this means is that the
LED turns on and off really fast. The brightness is a result of the
ratio of ON to OFF per cycle, thats pulse width.

The arduino makes this really easy. When you assign a value to an
analog output it translates that into a PWM ratio. So with a little
midi translation you should easily be able to take midi data and make
it into a value between 0 and 256 which you can send to a few analog
outputs.

BUT

you cant drive high power LEDs directly from the arduino.
A regular LED draws about 15mA. The arduino outputs can drive (I
think) around 20mA each.
A high power LED or LED array can draw at least a full AMP (1000mA).
The solution to this is a simple transistor based LED driver. A driver
is an amplifier and an isolator. It essentially takes very low current
from the arduino and outputs high current to the LEDs.
The kind of driver you use and the amount of current it supplies will
depend on the LED array you want to drive.




On Tue, Mar 27, 2012 at 1:45 AM, Jim Hickcox <tango.mceffrie at gmail.com> wrote:
> Thank you all for getting back to me.
>
> Patrick:
> I actually tried to call Enttec today, but both of their sales people
> were on an airplane, and they should get back to me tomorrow I guess.
> But what do you need? They have a usb to dmx, right? And then you need
> the driver, and then just the lights? That seems pretty
> straightforward.
>
> Max:
> That udmx looks awesome, if it's a functional thing.
>
> Jean-Marie/Björn:
> Thanks for the heads up on interface-z. I'd never heard of them. Looks
> easy enough.
>
> Charles:
> I guess I don't know how to just do a dmx output. Although, now I seem
> to have some options.
>
> Again, thanks all.
>
> -Jim
>
>
>
> 2012/3/26 Björn Eriksson <miulew at gmail.com>:
>> Found this when as suggested doing some googling on Interface-Z - on this
>> page some test pd patches and more...
>> http://www.interface-z.com/produits/act054_8_trans-puiss.htm
>> and a vid:
>> http://www.youtube.com/watch?v=JAjILa4MOu8
>>
>> /Björn Eriksson
>>
>>
>> On Mon, Mar 26, 2012 at 9:35 PM, Jean-Marie Adrien
>> <jma at jeanmarie-adrien.net> wrote:
>>>
>>> hi
>>> if you're in a hurry, google interface-z
>>> jmadrien
>>>
>>> Le 26 mars 2012 à 20:02, Jim Hickcox a écrit :
>>>
>>> > Hey there.
>>> >
>>> > I am working on an architectural installation with a guy and part of
>>> > the goal is to control some dim lighting from Pd.
>>> > Does anyone have any experience with the steps for taking the midi
>>> > output and making that control some LEDs?
>>> > Any recommended workflows?
>>> > I was thinking about trying to build something with an arduino, but
>>> > maybe there's something more time-efficient, since I only sort of know
>>> > what I am doing.
>>> >
>>> > Any suggestions would be appreciated.
>>> >
>>> > -Jim
>>> >
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