How to "fix" this ERC?

Schematic
1

I am using a LCD Display in a project.
The LCD Display has inputs for the Backlight. The Positive I am connecting to +5 volt power, but the Negative side I am connecting to a transistor to turn the backlight on and off. I get ERC because it’s not “connected” to Ground.
Thanks to any help
OtG

2

And that’s correct, ERC isn’t smart enough to know that it’s sometimes connected to ground. Put a PWR_FLAG on the ground of the LCD.

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3

May I ask why then you don’t “connect” it to the Transistor ? Kicad can’t Know what you intend to do with the backlight connections :slightly_smiling_face: I think that the day Kicad reports that I should use GPIO2 instead of GPIO4 because of possible software conflicts in the future I will put my hat on and go home :joy: But yes as @retiredfeline don’t forget the PWR_FLAG connection as we get a lot of that around here :grin: Good luck with your project.
:mouse:

4

Thanks that worked.
OtG

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5

“but the Negative side I am connecting to a transistor to turn the backlight on and off”
That’s what that means, I am. Adding a Power Flag cleared the ERC error.
OtG

6

Another way is to exclude that particular warning from being displayed.

The warning means: Hey I see a net with power Input pin but no power output pin. Are you sure power is supplied?

Putting a PWR_FLAG means: Don’t worry I’ve got this one.

Excluding the warning means: Shut up, I know what I’m doing.

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7

I’m wondering why the backlight pins are defined as power pins in the first place. That is what started this ERC violation.

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8

I just looked at three 16x2 displays, the HY1602E (A and K ARE passive, but pin out different than others listed below), the RC1602A and the WC1602A (using this one) BOTH have A and K as Power Inputs.
OtG

9

What is the difference between pins destined to power backlight and the pins to power IC?

10

Backlight are just a few LED’s, maybe an extra series resistance. It’s quite common to switch this on and off via some transistor, PWM it or have some other means to control brightness. Backlight for bigger LCD’s also tend to have multiple LED’s in series and can need 20 to 60 or so volt to run.

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