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Dave G
Dave G
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I'have been looking at the AdaFruit NeoPixels recently and am trying to understand how the addressing scheme works.

All of the examples I've seen explicitly identify the length of the string (number of neopixel units) and are typically set using an array of 24-bit values to control the color of a particular neopixel.

My question is two fold:

  1. How do the neopixels know where they are in a string to allow for addressing?
  2. If the neopixels know where they are in the string, would it not be possible to potentially feed the output of the last neoxpixel back to a microcontroller to determine the number of neopixels in the string?

OP Note (this is my interpretation and may be suspect, but it is more or less my take away)

Thank you for all the answers on this - it has been very enlightening from ALL of the answers. General take away, the NeoPixel is not "directly" addressable in the sense that you can pick pixel "X" of "n" pixels. The string of NeoPixels acts essentially as a gigantic shift-register (as stated in one of the answers) so to "address" a particular pixel you have to update a buffer that represents the state of the entire string and then shift it down the wire. This is why micro-controllers, such as an Arduino, would have limitations on how many NeoPixels it could control. This is also why it is more practical to define the number of pixels in the string and allocate memory to represent that state.

I'have been looking at the AdaFruit NeoPixels recently and am trying to understand how the addressing scheme works.

All of the examples I've seen explicitly identify the length of the string (number of neopixel units) and are typically set using an array of 24-bit values to control the color of a particular neopixel.

My question is two fold:

  1. How do the neopixels know where they are in a string to allow for addressing?
  2. If the neopixels know where they are in the string, would it not be possible to potentially feed the output of the last neoxpixel back to a microcontroller to determine the number of neopixels in the string?

I'have been looking at the AdaFruit NeoPixels recently and am trying to understand how the addressing scheme works.

All of the examples I've seen explicitly identify the length of the string (number of neopixel units) and are typically set using an array of 24-bit values to control the color of a particular neopixel.

My question is two fold:

  1. How do the neopixels know where they are in a string to allow for addressing?
  2. If the neopixels know where they are in the string, would it not be possible to potentially feed the output of the last neoxpixel back to a microcontroller to determine the number of neopixels in the string?

OP Note (this is my interpretation and may be suspect, but it is more or less my take away)

Thank you for all the answers on this - it has been very enlightening from ALL of the answers. General take away, the NeoPixel is not "directly" addressable in the sense that you can pick pixel "X" of "n" pixels. The string of NeoPixels acts essentially as a gigantic shift-register (as stated in one of the answers) so to "address" a particular pixel you have to update a buffer that represents the state of the entire string and then shift it down the wire. This is why micro-controllers, such as an Arduino, would have limitations on how many NeoPixels it could control. This is also why it is more practical to define the number of pixels in the string and allocate memory to represent that state.

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Dave G
Dave G
  • 155
  • 1
  • 6

Is it possible to infer the length of a neopixel string using 1-wire protocol?

I'have been looking at the AdaFruit NeoPixels recently and am trying to understand how the addressing scheme works.

All of the examples I've seen explicitly identify the length of the string (number of neopixel units) and are typically set using an array of 24-bit values to control the color of a particular neopixel.

My question is two fold:

  1. How do the neopixels know where they are in a string to allow for addressing?
  2. If the neopixels know where they are in the string, would it not be possible to potentially feed the output of the last neoxpixel back to a microcontroller to determine the number of neopixels in the string?