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Topic: 1-bit chainable shift registers? (Read 1 time) previous topic - next topic

bluebie

I'm looking to make very light-weight flexible tubes of individually addressable LEDs. Running wires for each LED would obscure light and make it rigid and heavy, so I am hoping to build a bunch of tiny PCBs with a circuit which acts as a chain able 1-bit shift register, so I can wire together any number of the boards with just a few flexible wires, then shift out new colour states to each of the LEDs.

Is there anything like this? I've been googling for hours, but the few things I have found, I don't understand.

Also, it's a portable application, so power efficiency is important, as well as using small components.

Thanks for your help.  :smiley-roll-sweat:

Graynomad

There are plenty of daisy-chainable shift regs with current-limited outputs, for example TLC5916 and TLC5926.

But can't you just buy one of the LED strips with the WS2801 chips built in?
______
Rob
Rob Gray aka the GRAYnomad www.robgray.com

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bluebie

Thanks for the replies, but these chips look to be 8-bit and 16-channel respectively, which would mean clocking out a whole lot of useless information just to turn a digital light on or off. I've played with LED strips, but couldn't find any which are suitably flexible in two axis (most just flex on one axis, as they're a flat strip). I also played with 'led pixels' - strings of lights with lpd6803 15-bit rgb lights. These are flexible enough, but require the controller output clock signal even when there are no updates to keep the pwm going, and all the preformed led pixels I could find were quite large - wouldn't really work in the sort of small tube I'm hoping to build, and all of them required 5 or 12 volts, which would mean including a boost converter as well, making a portable (wearable) project even heavier than it needs be, while probably wasting that extra power in resistors to convert the power back down to something suitable for the LEDs.

RGB and PWM are totally unnecessary, and I'd rather keep costs down, unless 3-channel drivers really are the only way to reasonably do this - I can probably get away with sending dummy data to pad things out if need be, but it just seems so wasteful.

What I'm most ideally looking for is essentially just one single stage of a parallel shift register. I saw some stuff about astable something or other flip flop things, but I don't understand any of it. I've only just gotten my head around PNP and NPN transistors, and most of the articles talking about these things don't seem to use terribly googlable phrases or be that helpful towards beginners. If someone could enlighten me on how these things work, that would be wonderfully helpful. :)

Graynomad

#4
Dec 04, 2011, 06:01 am Last Edit: Dec 04, 2011, 06:39 am by Graynomad Reason: 1
Quote
one single stage of a parallel shift register

AKA a flip flop (a shift reg is really just 8 flip flops). But how does having 1/8th of a shift register help. You still can't address it.

Quote
would mean clocking out a whole lot of useless information just to turn a digital light on or off.

What else is the processor going to do? Unless there are some serious timing constraints it doesn't matter if you have to clock out 500 bits just to change one of them.

None of the "standard" methods are addressable AFAIK. The only way to get addressing of individual LEDs is to put a processor at each LED or a shift register AND an identity comparator AND a DIP switch or method of setting the address.

So apart from not wanting to shift "useless" data is there any other reason for wanting to address individual LEDs?

______
Rob
Rob Gray aka the GRAYnomad www.robgray.com

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