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If I have a string of lights in series, like a christmas tree string of lights, is it possible to turn on 1 of the lights with an intelligently regulated voltage from a raspberry pi. I have found a resource stating the fastest GPIO voltage regulation time to be in the 22 MHz range.

http://codeandlife.com/2012/07/03/benchmarking-raspberry-pi-gpio-speed/

Can I, with a combination of changing the input and output voltage of a raspberry pi, create a waveform that could light up a single light or even a discrete set of lights in that series?

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    \$\begingroup\$ Not if they are in series. \$\endgroup\$ – Leon Heller Apr 21 '17 at 14:53
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    \$\begingroup\$ I think OP is hoping to have a sort of stationary voltage wave in the chain. But yeah, that's not how electronics work. \$\endgroup\$ – Vladimir Cravero Apr 21 '17 at 15:20
  • \$\begingroup\$ Series inherently means all lights are powered simultaneously via a single control signal. To reference individual lights or groups of them you need a parallel wiring with appropriate switching mechanisms in place. \$\endgroup\$ – Jarrod Christman Apr 21 '17 at 16:52
  • \$\begingroup\$ Anything is possible \$\endgroup\$ – Voltage Spike Apr 21 '17 at 16:57
  • \$\begingroup\$ Not in series no. If they are in parallel, it is theoretically possible to do what you suggest, though you would need some really really fast electronics to do it. \$\endgroup\$ – Trevor_G Apr 21 '17 at 17:38
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You can use strings of WS2811 digitally-addressable RGB LEDs.

Each WS2811 provides RGB colour from 3 x 8-bit digital input data.

Each contains 4 connections: serial input, serial output, ground and 5V. The devices can be connected in long daisy chains, with one WS2811's serial output driving the serial input of the next WS2811 and all 5Vs and GNDs in parallel. You can buy them pre-assembled into chains of ten for a fiver, longer chains for more.

Have a look on the interweb for WS2811, the datasheets and supplies are freely available. I think there's an Arduino driver for them so there may well be Raspberry Pi software, too.

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