Here’s a quick project to get some funky flashing / colour changing LEDs into your pumpkin. Just grab a set of addressable WS2812‘s and some Arduino code and your’re done.    The 2812’s are pretty easy to wire up.  Essentially, +5v, GND and data signal get daisy changed through the set of LEDs.  Each LED has 3 pins for IN and 3 pins out.  Wire from the Arduino to the first IN set, then from that LED’s OUT set, to the next LED.  Repeat until all the LEDs you want are connected.   Then, load the below Arduino code, ensure you have the right pin assignments and identify the number of LEDs in the string and you’re done.  Also be careful to monitor the current draw of the LEDs if you are wiring directly to the Arduino.  Most have current limits and can only power a few LEDs. I managed 5 LED’s with a knock-off Nano just fine.   You can always wire power to an external 5V power supply.  Just ensure you make the grounds common by ensuring both the controller and power supply grounds are connected.  Check out the video below to see the effects.

 
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Code:  ArduinoSketch

Code Reference