I bought a string of 5v lights off ebay and connected them to an

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I bought a string of 5v lights off ebay and connected them to an Arduino Uno. I setup DemoReel100 to check the lights.

Now I’ve placed them in a mesh grid to simulate a Christmas tree. Video will be posted shortly.

http://markcahill.com.au/arduino-controlled-led-lights/

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I see you have put a resistor from the Arduino to the data line. Why ? Is it necessary? Adviced ? Thank you

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@Yves_BAZIN Other than just a real world best practice- this is the best explanation I have found:

“The resistor is there to limit the current into the input pin. The input likely has a very high DC resistance (more than 1 megohm) so negligible current flows (on the order uA) and a negligible voltage drop is produced (on the order uV or mV). The resistor is likely used to slow the slew rate of the connection (the input pin will have some capacitance, so adding a series resistor forms an RC circuit) to prevent overshoot and ringing which could cause issues with the communication. It also prevents the I/O signal from trying to power the LED string through the ESD protection diodes by limiting the current to something that will not damage the internal diodes.”

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@Tom_Schubert thank you. I see that Mark as put an 220ohm resistor what is a good range for this ?

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@Yves_BAZIN I was pointed to this Best Practices for similar questions. Maybe this can help you too: https://learn.adafruit.com/adafruit-neopixel-uberguide/best-practices