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On Wed, Jun 20, 2007 at 08:59:19PM -0400, Rolf wrote:
> Anyway, I have completed my project, and it is based on 8 RGB LED's 
> (that's 24 individual LED's). These LED's are mounted in the stage of 
> the Theater, and illuminate the puppets, etc. ***  Each LED is 
> individually controllable using PWM. I based the control on the 
> PIC18F4620. With 6 buttons to control the different lighting modes 
> (strobe lights, rainbow colours, chasing lights, sound-sensitive, 
> manual, off), and 4 knobs on A/D channels to control the R, G, B and 
> Special Effects respectively, I am using 34 IO pins. This leaves the 
> power pins, and some of the ICSP pins unmuxed. Anyway, without the knobs 
> and buttons you could probably get 10 RGB LED's controlled by the 
> 18F4620 (or 32 normal LEDs). You will struggle to get more LED's than 
> that as well as keep pins available for comms to the master node, and 
> power pins... (and have enough time in the interrupt routine to control 
> the LED's).

Yes definetely. I've found software pwm can be surprisingly hard to
actually implement, it soaks up so many cycles.

> Bottom line is that, if I were you, and based on my recent experience, I 
> would consider setting up 30 LED's per mini node, and putting all the 
> control mechanisms on that mini-node, then feeding out a whole bunch of 
> wires which just have the LED attached to the ends (in a star topology). 
> Then, have a separate power and control bus to a master node that can be 
> your real expansion point....
> 
> Anyway, if you are interested I am happy to share all my work including 
> Eagle PCB drawings and C18 code (with mostly assembler interrupt 
> routine...).

That'd be great thanks. Share it under the GPL, then that way, if I or
anyone else ends up using any of your code, you'll get credit in the
copyright notices of anyone who uses it.

> I was also thinking of your cost, and I figure with a trip to Active 
> Surplus (you are in Toronto, right?), you could get that really cheep 
> 'phone' wire that they have near the back (a single twisted pair) at a 
> better rate than the $0.10/ft they advertise, and then you could 
> probably save a bunch of money by having about 1 thirtieth of the PCB's 
> but they would be more complex..... each LED would simply be a LED 
> soldered to the end of a wire with some heat-shrink. All the resistors, 
> regulators would be on the remote control board....

Ahh, yeah I saw the wire the other day actually. Though as I mentioned
in another post, turns out you can get CAT5 cable a *lot* cheaper than I
thought.

> *** actually, I have 16 RGB LED's, but I have 8 shining up from the 
> stage, and 8 shining down on to a white-board for cool effects.... There 
> are 8 light "boxes" and the 2 RGB LEDs in each box are wired in series. 
> Because the G and B LED's have high forward voltages (4.5V which in 
> series is 9V, I am driving the LED's at 12V, but the PIC at 5V).

12V 'eh? With no resistors, or are you relying on pwm to limit the
average current?

- -- 
http://petertodd.org
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