ERC complaining about Power Input even with PWR_FLAG

I am getting the following ERC warnings:


Usually when that happens I know that I have forgotten to put mark the PWR_FLAG, but this time even if I add the PWR_FLAG to +5V and GND I still keep getting the same issue.

Could someone please explain this to me (I am kinda new to KiCad)

You’ve got a 100 ohm resistor between +5V and pin 8 so they are not the same net. Sure it’s supposed to be wired up that way? If you look at page 5 of the datasheet, the LED current doesn’t go through the resistor, which is why your circuit looked sus to me.

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I agree with kenyapcomau on both comments. The LED current should not go through the 100 Ohm resistor, which would cause a voltage drop in the Vdd of the IC:

(The cap with value 104 = 100nF, which is 47 times smaller then OP’s.)

kenyapcomau is also right about the power flag warnings. Putting those resistors in series with Vdd makes it a separate net, so the pin’s 8 of each chip are not connected to the net with PWR_FLAG.

There are at least 3 different ways to resolve this:

  • Ignore the ERC errors, as you know better than KiCad in this regard (KiCad V6 is likely to get flags so you can instruct it to ignore certain ERC errors, while it would not clutter up the ERC errors list window)
  • Put PWR_FLAG symbols direct on Vdd of each IC.
  • Change the WS2811 symbol and set pin 8 to “passive” instead of “Power Input”.
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I would also suggest that you avoid drawing four way connections - I know that you have explicitly added a junction but they are frequently the source of confusion.

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Thank you guys, I had completely missed the placement of the resistor. That would have been a expensive miss. I understand the PWR_FLAG better now.

See, not only do you get your KiCad questions answered but also circuit design ones. This forum is great value, eh? Tell all your friends. :laughing:

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Nothing wrong with 2 way junctions and connection dots. Last time this was an issue was somewhere in the 80’s with bad quality dot matrix printers.
There is a very simple converntion that works good:
With a dot there is a connection. No dot, no connection.

Related to this:
Never draw those weird “bows” to jump over connections, when hand- drawing a schematic. Doing so is pretty much un-maintainable, as you always have the inlination to draw the bows on the last drawn wire, which would make some bows horizontal, and others vertical. When the screenshot below would be drawn on paper, with the bows, it would look truly confusing:

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Ah, we are junction dotting again. Better read the old threads and take the flame suits, clubs and medieval body armors from the closet.

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Hey, Jon started it :slight_smile:

The first 2 flame threads from today’s search:
https://forum.kicad.info/search?q=junction%20dots

are:


and these may give you some warmth inside, now summer is slowy turning into autumn, winter next, on the top side of this dirt ball.

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It’s comforting to know that some things never change.

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Hey now, what i said was four way junctions which can always be drawn as two three way junctions. Anyhow I’m not going to say another word! Ziltch, zero, nothing, rien, nada. :smile:

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