I have here some fairly lights. It's a string of coloured LEDs with a transformer and control box at one end. The control box lets you select a bazillion different lighting patterns. (Presumably the box contains a small microcontroller. I suspect it uses PWM to dim the LEDs.)
There are 4 colours of LED, but they always light in pairs. This leads me to believe they're wired as two independent circuits. Presumably wiring each colour individually would use twice as much wire, which would eat into the manufacturer's precious profit margins.
This got me thinking... Is there some way you could connect all the LEDs to a single circuit yet still be able to control them independently? In particular, I'm wondering if you would connect each LED across the power rails in series with some sort of trivial passive band-pass filter. That way, the microcontroller can generate some complex multi-band waveform, but each LED only receives a narrow(ish) frequency band to light it.
Basically, I'm wondering if something similar to this could be made to work:
Where each colour of LED has a band-pass filter tuned to a different frequency. (I gather capacity on its own isn't really a functioning filter...)
To be clear, I doubt this would end up actually being any cheaper to manufacture. But I'm wondering if it's technically possible. (I'm also not intending to try to make it, just figure out what the schematic would look like.)