Is it possible to sync color changing LEDs?

[kalel]

Is there any way to sync multiple color changing LEDs such as those available on eBay?
The fast and slow 2 pin flashing kind with built in ICs.

Probably not, but I thought I could ask the experts here.

Thanks.

[ataradov]

No, it is impossible. They use internal RC oscillator for timing, and those things are not super accurate.

[rs20]

Well, it might not be impossible. Probably just very difficult and not worth it.

For example, perhaps modulating the voltage will modify the frequency of operation, allowing controlling circuitry to wrestle them into sync.

But this would be a silly solution of course; it's far easier just to get RGB LEDs and drive them yourself.

[ataradov]

For example, perhaps modulating the voltage will modify the frequency of operation, allowing controlling circuitry to wrestle them into sync.

But then they will drift with temperature, so you need a feedback loop, so RGB light sensor for each LED

It is easier to create another universe, where all RC oscillators are synchronized

[rs20]

But then they will drift with temperature, so you need a feedback loop, so RGB light sensor for each LED

RGB light sensor is overengineering! Much cheaper and more reliable to just monitor the LED's current draw variations...

[ataradov]

RGB light sensor is overengineering! Much cheaper and more reliable to just monitor the LED's current draw variations...

Not going to work. I'm pretty sure there is more than one combination of R, G and B that results in the same exact current.

[rs20]

Not going to work. I'm pretty sure there is more than one combination of R, G and B that results in the same exact current.

Is that a CHALLENGE? 

[0b01010011]

if they are reasonably slow changing could you perhaps power cycle the LEDs together for a short time each RGB fade cycle.

you'd have to assume each RGB fade cycle is, say 4 seconds, and then power cycle for maybe 30ms every 4 seconds.

This way they'd be reset each time so won't drift apart, but if they are significantly different in RC timing then of course this won't work.

[james_s]

If you want to synchronize a bunch of RGB LEDs, why not just use regular RGB LEDs without a built in IC and then a separate controller to drive as many of them as you want? You can even buy controllers that are pretty much plug & play.

[edavid]

You wouldn't think it would be possible, but I believe that's how this type of LED flashing heart kit operates:  http://www.ebay.com/itm/DIY-Kit-Love-Heart-shaped-LED-Colorful-Light-Water-Electronic-Flashing-/232266480711

Here's a review that has some detail and waveforms: http://goughlui.com/2016/11/07/project-at89s52-based-multi-coloured-led-heart-kit/

[ajb]

You wouldn't think it would be possible, but I believe that's how this type of LED flashing heart kit operates:  http://www.ebay.com/itm/DIY-Kit-Love-Heart-shaped-LED-Colorful-Light-Water-Electronic-Flashing-/232266480711

Here's a review that has some detail and waveforms: http://goughlui.com/2016/11/07/project-at89s52-based-multi-coloured-led-heart-kit/

That's just turning them on and off in sequence so that they're not on long enough to get too out of sync.  Even so, at about 1:10 into the video of the kit in action you can see some patterns where they're on long enough to start getting out of sync. 

You can use the inconsistency to to good effect by installing a bunch of them together in some sort of diffusion and get all sorts of pseudo-random color combinations.

There are some 2-pin RGB LEDs that use a sort of one-wire interface, used in some color-changing holiday lights.  I  have a few such strings where the supply voltage is switched between ~3V and 5V for signalling, and the LEDs each have one of I think 8 fixed addresses so you can do sequences across the string.  Only downside is that the nature and low speed of the interface causes a visible dimming of the whole string whenever anything is transmitted.

[Jeroen3]

Synchronizing fireflies?
https://tinkerlog.com/2009/06/25/64-synchronizing-fireflies/