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NeoPixel: 9 out of 16 light on a strip
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NeoPixel: 9 out of 16 light on a strip

by vinbedded on Fri Mar 19, 2021 11:35 am

Hello,
I made a custom board with NeoPixel Mini 3535 devices. I reflowed two boards with my own reflow oven. The first board did not work out as well due to the oven needing calibrating. After calibrating I reflowed the first board, everything looked ok, but not all the LED's would light up which I figured was due to reflowing the board multiple times during calibration. The second board I made the reflow oven worked like a charm, all connections looked good, LED's looked perfectly aligned. Powered up the board, but none of the LED's lit up. Same exact code used on the first board was used on the second board. I adjusted the timing slightly in the code, and the board magically started working, but only the first 9 LED's worked out of the 16 on the strip. I am driving two 16 LED strips with the same signal (see attached schematic), the strip on the right works as expected, but the one on the left only 9 LED's work. I used my scope and checked the DOUT signal of each LED and it all looks good going to the last LED.

What could possibly going on here? If these LED's are this sensitive to reflowing, it will be difficult to make more than 1 board.
I have a decoupling cap for each LED.
Where I am driving two strips, does each strip need the 470 ohm resistor, as far as I can tell signal looks good.

Thank you,
-Vinny
Attachments
NeoPixel.pdf
NeoPixel schematic
(185.57 KiB) Downloaded 3 times

vinbedded
 
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Re: NeoPixel: 9 out of 16 light on a strip

by franklin97355 on Wed Apr 07, 2021 11:50 am

I don't know about the newer pixels but the ones made were very specific on the storage and the temperature profile used and we had difficulty in making boards without keeping an eye on them. The description section has a part of it that says "These raw LEDs are cut from a reel and/or might be loose. They may not suitable for pick & place + reflow. LEDs are notoriously difficult to use in an automated process due to being very sensitive to moisture and temperature. We recommend these for careful hand soldering only!"

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Re: NeoPixel: 9 out of 16 light on a strip

by vinbedded on Sun May 09, 2021 10:32 pm

In this case my hand was the pick n place machine. I have never heard that smd leds are difficult in an automated environment. These are too small to hand solder because they are very close together on the board that I have and very small to begin with. I chose these because of their size. I think you are looking at the wrong product page. The leds I am using are here https://www.adafruit.com/product/3484
This page does not mention a pick n place + reflow problem.
Last bumped by vinbedded on Sun May 09, 2021 10:32 pm.

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