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When are LEDs intensities changed during setPixelColor
Moderators: adafruit_support_bill, adafruit

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When are LEDs intensities changed during setPixelColor

by Tom_TBT on Wed Aug 12, 2020 8:43 am

Hello,
I am a researcher working on the retina, and I'm using Adafruit NeoPixel Digital RGB LED Strip 144 LED - 1m White - WHITE for a project. Timing is extremelly important and I need to know how the LEDs are updated when transmitting new values.

Are the LEDs changing sequentially, as they receive the new values, or do they all change at the same time once the setPixelColor is done?

Thank you!

Tom_TBT
 
Posts: 3
Joined: Wed Aug 12, 2020 8:32 am

Re: When are LEDs intensities changed during setPixelColor

by adafruit_support_bill on Wed Aug 12, 2020 8:58 am

setpixelcolor() works on an array in memory. The colors are not written to the pixels until you call the 'show()' function.

For details on the timing of the actual transmission of data to the strip, see this topic: https://learn.adafruit.com/adafruit-neo ... aq-2894689

If timing is critical, Dotstars may be a better choice: https://learn.adafruit.com/adafruit-dotstar-leds

adafruit_support_bill
 
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Re: When are LEDs intensities changed during setPixelColor

by Tom_TBT on Wed Aug 12, 2020 9:19 am

Sorry yes, I meant the show() function.
So if I get it correctly, the new colours are latched all at the same time, 50us after that the last bit of data is transmitted.

Thank you

Tom_TBT
 
Posts: 3
Joined: Wed Aug 12, 2020 8:32 am

Re: When are LEDs intensities changed during setPixelColor

by adafruit_support_bill on Wed Aug 12, 2020 9:40 am

Correct. The colors are latched on the chip 50us after the last bit. But the refresh rate of the LEDs is 400Hz, so it could be as long as 2.5ms after latching before that color is actually visible.

Dotstars are considerably faster with a 19.2KHz refresh.

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Re: When are LEDs intensities changed during setPixelColor

by Tom_TBT on Wed Aug 12, 2020 10:02 am

I see, thanks a lot for all the informations

Tom_TBT
 
Posts: 3
Joined: Wed Aug 12, 2020 8:32 am

Please be positive and constructive with your questions and comments.