Flickering Neopixels

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gillerire
 
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Flickering Neopixels

Post by gillerire »

Hi guys,

Hoping somebody can offer some advice on a problem I'm having.

I'm building a square infinity mirror. I'm using 40 neopixel 8mm LEDs (10 down each edge) that are controlled by a trinket and powered by a 12V plug-pack.

I had a bit of a false start early on by trying to power the pixels through the trinket's 5V output pin. The pixels did not respond to the trinket's signals and just flickered weirdly. I assumed it was because they were not getting enough power.

So I added a 7805 regulator to power the pixels and suddenly everything lights up and the trinket signals are being sent. However, the pixels on the end of the data string flicker and sometimes change the wrong colour. The last pixel is the worst and then it gets less noticeable until the effect goes away at about pixel 30.

I did a little experiment and tried using just the first 10 pixels. I was surprised to that the effect was still there - although now only noticeable on the last two or three pixels.

Any ideas on what might be causing this and how to fix it?

I have followed the neopixel power guide, such that I'm using a 1000uF cap on the power rail and a resistor of the suggested value on the trinket signal pin.

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adafruit_support_bill
 
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Re: Flickering Neopixels

Post by adafruit_support_bill »

What power supply are you using to feed the 7805? Is it getting hot?
Also, are you feeding power to multiple points on the strip, or just at the start? Try feeding power to both ends.

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gillerire
 
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Re: Flickering Neopixels

Post by gillerire »

Hi Bill, thanks for the reply.

I'm using a 12V plug-pack. Yes, I have noticed that the 7805 is getting hot. I have been running the pixels at around 10% brightness to try to overcome that. Now that you mention it, I did notice that the flickering was much worse with the pixels at full brightness.

Should I be using a lower voltage power supply? I was actually going to ask this as an aside but maybe this is the actual problem!?

The neopixels' 5V and GND pins are all connected together in a loop so I think the power is being distributed evenly.

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adafruit_support_bill
 
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Re: Flickering Neopixels

Post by adafruit_support_bill »

The 7805 is a linear regulator. That means it burns off the excess power as heat. With 12v being regulated down to 5v, that means 60% of the power is wasted. You would be better off with a 5v switching power supply. These are generally much more efficient.

40 pixels would pull about 2.4A worst-case. The 2A supply should be enough if you run at less than about 80%. We also have a 4A supply.

https://www.adafruit.com/products/276
https://www.adafruit.com/products/1466

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gillerire
 
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Re: Flickering Neopixels

Post by gillerire »

I see - and do you think that will solve the flickering issues?

I'm in Australia so might try to source locally rather than need to buy an adaptor, but thanks for the links.

Just to be clear, you're suggesting that I get rid of the 7805 completely and power everything through a 5V supply?

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Re: Flickering Neopixels

Post by adafruit_support_bill »

What you describe is consistent with the 7805 going into 'thermal shutdown' due to overloading. You can power both the Trinket and the LEDs direct from the 5v supply. That would be the most efficient way. I would expect you can find a 5v power brick locally.

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gillerire
 
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Re: Flickering Neopixels

Post by gillerire »

Awesome - thanks a lot for your help!

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