Neopixels Flickering when fading

Hi all, ive got a strange thing when trying to control neopixels.
When powering from the 5V usb line, all goes well.
But when using an external more powerfull supply things go haywire
see movie
Power source is a 12V AC, rectified with a big capacitor (swapped multiple also tried a smaller one on the 5v line of the neopixels) and using a l7805cv to goto 5 volt. ( also tried i more expensive voltage regultator)
Multimeter measures 5volt exactly.
Anyone got any idea where it comes from?
(ps they are RGBW leds, when using only RGB the issue does not appear)


You may have better luck getting an answer at the Adafruit forum:

Power source is a 12V AC, rectified with a big capacitor (swapped multiple also tried a smaller one on the 5v line of the neopixels) and using a l7805cv to goto 5 volt.

You need a diode in that mix. Why not post the schematic?

there is a rectifier bridge before the capacitor :slight_smile:
ill try to post the schematics this evening

Check if that 5V/12V is from a PWM control rather than a regulated voltage. PWM usually is below 1kHz, and if its under 500Hz, you will see flickering. Dont forget that the mains voltage in most countries is EU are 220V 50-60Hz. That frequecy might be causing this flickering.


Please read the first post in any forum entitled how to use this forum.,148850.0.html then look down to item #7 about how to post your code.
It will be formatted in a scrolling window that makes it easier to read.

Thanks.. Tom.. :slight_smile:

I cannot post the code, because that exceeds the maximum length (9000 chars)
thats why i posted the link,
attached is a quick schematics, where the wifi module in fact is a NRF24L01 module,
the first capacitor is 1500u @ 20V, and the second is a 330u
the resistor is 470 Ohm, total of 9 neopixels are connected

Can you please post your code as an ino attachment please?

Where are the capacitors that are required around the two regulators?
Check the data sheets, the capacitors help with noise and regulation performance.
They should be placed a close to the regulators as possible.

Can you please post a copy of your circuit, in CAD or a picture of a hand drawn circuit in jpg, png?
Including component labels and values.
Sorry, not a Fritzy picture.

Have you got the neopixel gnd connected directly to the gnd connection of the 7805 regulator?
Have you got the neopixel 5V connected directly to the 5V output connection of the 7805 regulator?

Can you post a picture of your project please so we can see your component layout?

Thanks.. Tom.. :slight_smile:

Hi tom, thanks for taking the time to look at this :slight_smile:

all grounds are connected together
the 5v output from the 7805 has 3 lines, one to the arduino, one to the pixels and one to the le33
attached are pictures, sketches and code :slight_smile: .
tried adding the capacitor between + & - and in between the 7805 and the le33, but that didn’t seem to help.

I also tried to replace the 7805 with a LM2596 DC step down converter to give the 5 volts, but that also created the flickering.

arduinocode.txt (12.4 KB)

You need to add these capacitors, even if it does not fix your problem.

Tom… :slight_smile:

Ok also if i have the 1500 u on the 8705 input and the one on the output of the le33 ? so add 4 capacitors, totalling to 6 ?

You have electrolytic capacitors fitted, they are okay for filtering the AC ripple and major surges.

You need the smaller capacitors as close as possible to the reguator pins to help noise and regulator response.

So the 0.33uF and 0.1uF should and will not be electrolytic.

The 2.2uF should be a tantalum, but an electro will be fine as long as you place it as close as possible to the regulator pins.

Not all capacitors are created equal, different types/construction are needed for different jobs

Hence you will see for example a 1000uF electro in parallel with a 0.1uF monolithic.

In an ideal world a 1000uF capacitor would filter and bypass from DC to daylight.

However in the real world, your 1000uF capacitor has to be an electrolytic which has frequency response limits.
So a 0.1uF Monolithic will take care of the higher frequency bypass function that the electro cannot.

Tom... :slight_smile:

Ok thanks for the insight, i will try if i have some of those lying around :slight_smile:

That didnt work, but it seems that the White command is what causes the issue.
When only fading RGB values and leaving the white value on 0, or only fading the White and leaving the rgb on 0 doesnt give any issues.
So changed my code to only change rgb values or only change white levels.

Have you measured the power supply at the neopixel strip when the problem occurs?

Tom.. :slight_smile:

If I may ask; Do you power the neopixels with 3.3V and controlling them with 5v logic? If so, this could be the cause of your problem - using 3.3v logic on neopixels powered with 5v will cause similar issues.

EDIT: Forget it, got the screen shot schematics wrong :slight_smile:

Nope, whole system is powerd @ 5V, measuring the neopixels show exactly 5 Volts.
Power supply is sufficient, 0.3 Amps & 12V AC

Those neopixels are rather hungry, one RGBW pixel takes up to ~80mA. You have at least 9 which is ~0.7 amps. A power supply with 0.3 amps is not sufficient for all the stuff you are driving with it :slight_smile: