Hi everyone! I have a question for you.
Why is there a capacitor placed only on the 3.3V line and not on the 5V in this wiring diagram published on the official WLED website?
Shouldn’t it be the other way around?
The diagram I’m referring to is the first one, titled “5 volt digital LED strip wiring diagram”, at the following link:
If you are talking about the 100nF ceramic decouple capacitor above the level shifter, it is there to filter out switching noise and fluctuations of the power supply when the shifter is switching at the high frequency that LED data uses.
Sorry, I hadn’t specified — I mean the electrolytic capacitor between GND and 3.3V on the ESP32. Shouldn’t it be on the 5V line instead?
Ah gotcha. The esp chip on the board runs off of 3.3v and there is an onboard converter connected to the 5v side that drops the voltage to 3.3v for the esp chip. So really you could put the cap in either location. It may be slightly better/faster at regulating the power direct on the 3.3v side.
TBH I have never needed to add a Cap to either location. But I also use quality Mean Well power supplies and wiring that is capable of providing power without dips. It is very likely that you do not need the capacitor. If you find your controller having reboot issues, that would be a sign of power dips and it browning out and resetting. In such a case the cap may help, but in reality if you need that cap you have other power issues (most often times it being a junk power supply).
The reason I put it in the official wiring guide is that a cap on the 3.3V line helps with stability of wifi on some boards, a cap on the 5V rail can also help but it is optional.
It is not always required and depends on the controller used: if its well designed its not needed but unfortunately most cheap ESP hardware is designed for cost not stability.
When wifi is transmitting, it draws high-current spikes (roughly 3x the normal amount). If the 3.3V regulator used is not fast enough to keep delivering that spike, wifi becomes unreliable, crashes have also been reported. The cap adds more buffer to even out the spikes, putting it on the 5V rail still needs the regulator to be fast enough so its not as effective.
The wiring diagram is showing a setup that is proven to work well, it does not mean that its the only way.
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