Arduino Uno R4 WiFi
60 LEDs of WS2812B strip (5V, ~3.6A max draw)
External 5V 5A power supply (shared ground with Arduino)
Problem:
When I power the strip only from the external 5V supply (Arduino still on USB for logic), the LEDs flicker randomly, especially at high brightness or white color.
But when I power both Arduino and strip from USB (limited current, so only ~10 LEDs lit), it works perfectly—no flicker.
I’ve already:
Connected GND of PSU to Arduino GND
Added a 1000µF capacitor across PSU output
Used a level shifter (74HCT125) for data line (since Uno R4 is 3.3V logic)
Kept data wire short (<20cm) and away from power lines
Observations:
Flicker looks like data corruption, not power sag (voltage stays ~4.9V under load)
Happens even with setBrightness(50)
Same PSU works fine with a commercial LED controller
Question:
Could this be a ground loop, noise on data line, or timing issue with 3.3V → 5V signaling despite the level shifter?
I actually tried removing the 74HCT125 level shifter and added a 100Ω resistor directly between the Uno R4’s pin 6 and the WS2812B data input—kept everything else the same (shared GND, cap on PSU, etc.).
But the flickering got slightly better at low brightness, but at full white or high saturation colors, it’s still random LEDs glitching to red or turning off briefly.
At low brightness , the strip runs perfectly stable.
But as soon as I go above ~70% brightness or use white / high-saturation colors (which draw more current), the flickering starts: random LEDs flash red, green, or just drop out for a frame.
So if you do the previous 10 LED test but with your external PSU, how it behaves?
You likely have PSU that is labeled for current that it can't supply...
Superficially, should be good. Evidence says the power supply is failing, OR your actual wiring is inadequate. Please provide a clear, high resolution picture of your hookup. For example, a Dupont style connector will not be adequate for anywhere near 3.5 Amps of current.
