Drew Van Zandt wrote: > The flexible PCBs are insanely expensive in small quantities.
That's if you farm it out, right? What if you etch it yourself? That should be practical if you can get by with a single sided board with SMD components. Can you get the flexible substrate for a reasonable price? If not, perhaps it can be hacked together using something like a thin sheet of polypropylene (often sold as temporary cutting boards) with some self-adhesive copper adhered to it. Then there is the approach of drawing the circuits using conductive paints. Instructables.com is full of projects for making flexible circuits. Now that I look at the picture of what David wants to make, I see the curve in question is actually a flat 2-D circle. Not what I expected. So there's really no need for a flexible circuit. A simple flat, rigid PCB will do. This is going to pose some challenges to the legibility of your text, as you are going to have varying dot density as you go from the inner to the outer circles. "That's roughly a 30" circumfrence." -that's a lot of LEDs! David Kramer wrote: > Since the background needs to be > white, I was thinking of using foamcore boards > http://en.wikipedia.org/wiki/Foamcore > > ...I should be able to just push the LEDs through... Do you want the unilluminated LEDs to be visible protruding from the mask? I had assumed the LEDs would be mounted from behind and visible through some sort of a window (smoked or mirrored). > ...and bend the leads out which should keep the LEDs relatively > straight. Rather than pushing the leads through the foamcore, another option would be to punch holes through it that are slightly smaller than the LED bodies (assuming you use traditional round body LEDs), such that when they are inserted they'll be flush with the outer surface. In theory, if you could get your math and assembly tolerances good enough, you could still use SMD LEDs mounted to a flexible circuit. But good luck getting 100+ LEDs to line up with 100+ hand punched holes. A little CNC help would be good. The simplest approach I can think of is to make the outer circle entirely from a single-sided PCB, with no traces on the side that the LEDs mount on (and thus you'd use through-hole LEDs), and paint the board white. > It's been decades since I made a PCB. While that would certainly be the > neatest solution (though not the lightest), I'm definitely not up to > making a PCB with hundreds of trace lines all going to the same general > area. It's not trivial, but it may be much easier than you think. You wouldn't "hand tape" the board. You'd do the layout in software. You've then got 3 options to manufacturer it: 1. farm it out for professional production; 2. find someone with a CNC router to do it; 3. make it yourself by using one of many techniques, such as toner transfer from a laser print to the board. As for weight, use as thin substrate. Or hack something together like substitute plastiboard (similar to foamcore, but waterproof) with self-adhesive coper applied to it. > I feel if I go this route instead of the mechanical rotating ring > design, though, I'll end up with a much better product and more > experience in embedded software. Actually I think the best option is to ignore everything above, and combine the two designs: rotating electronic LED display. http://www.youtube.com/watch?v=ML6ZrWKTWPo It eliminates a whole pile of challenges mentioned above, like getting hundreds of LEDs wired up and evenly spaced, and the dot density problems I mentioned. Now you only have to deal with driving 8 or 10 LEDs. And making them RGB becomes far more practical. You just need to figure out how to get them to spin at a few hundred RPM without being too heavy (use a stepper motor from an old floppy drive?), being a danger to yourself and those around you, how to synchronize your message with the rotation, and how to get power and/or signals onto the spinning mechanism. -Tom _______________________________________________ Hardwarehacking mailing list [email protected] http://lists.blu.org/mailman/listinfo/hardwarehacking
