Author Topic: KiCad6 - Error: Input Power pin not driven by any output power pins  (Read 786 times)

0 Members and 1 Guest are viewing this topic.

Offline newtekuserTopic starter

  • Frequent Contributor
  • **
  • Posts: 334
  • Country: us
I know this subject was beaten to the death in multiple places, I've read about it on reddit, on eevblog, youtube, other lesser known sources... typically I solve this by just adding the POWER_FLAG to either the ground or +5V connection, but for some reason, this pin of the 16x2 LCD is giving me trouble.

The schematic is simple, pin 15 goes to a 330ohm pull-up resistor. This is with a symbol downloaded from snapeda because Kicad only knows about obscure LCD screens for some reasons which don't match my HW.

Could this be a problem with the symbol, or I'm doing something wrong? If so, what?

I also tried connecting this pin directly to the only other PWR_FLAG I have in my circuit and I get the same error.

 

Offline langwadt

  • Super Contributor
  • ***
  • Posts: 4392
  • Country: dk
Re: KiCad6 - Error: Input Power pin not driven by any output power pins
« Reply #1 on: February 26, 2023, 01:37:47 am »
I assume A and K is the Anode and Kathode of the backlight.

So the symbol have be made with the assumption that A would connected to a supply and the current limiting from K to ground.

You have K connected to ground and the current limiting from A to supply

So either change the symbol or move the 330R resistor to the K line and connect A to 5V
 

Offline newtekuserTopic starter

  • Frequent Contributor
  • **
  • Posts: 334
  • Country: us
Re: KiCad6 - Error: Input Power pin not driven by any output power pins
« Reply #2 on: February 26, 2023, 03:24:02 am »
If I remove the 330ohm resistor from the anode I no longer get errors, but why? Why does KiCad not like that I'm trying to limit the current to the LCD?
 

Online SiliconWizard

  • Super Contributor
  • ***
  • Posts: 14306
  • Country: fr
Re: KiCad6 - Error: Input Power pin not driven by any output power pins
« Reply #3 on: February 26, 2023, 03:26:54 am »
The LCD symbol has likely tagged the anode pin of the backlight as a "input power", explaining the warning/error.

I do not recommend that - generally speaking diode pins should just be tagged "passive" IMO.

But as a more general rule, the idea is that KiCad doesn't know that whatever net is after a resistor, even if said resistor has its other end connected to an "output power", is also an "output power". And it sort of makes sense, as ERC is a pretty basic rule check and is not meant to analyze your circuits and if they are designed properly.

So here, to silence the error, you can either just set it as an exception in KiCad and not change anything - it will not come back. Or, you can modify the symbol to set the anode pin as passive. Or, you can attach a 'PWR_FLAG' to the net between the resistor and the anode, which is how it's usually done.

 
The following users thanked this post: newtekuser

Offline newtekuserTopic starter

  • Frequent Contributor
  • **
  • Posts: 334
  • Country: us
Re: KiCad6 - Error: Input Power pin not driven by any output power pins
« Reply #4 on: February 26, 2023, 03:37:28 am »
Madness, but it worked... added the power flag between the Anode pin and the resistor, no more errors. Ignoring it was my thought but I'm a bit OCD.

Thanks all!
 

Offline langwadt

  • Super Contributor
  • ***
  • Posts: 4392
  • Country: dk
Re: KiCad6 - Error: Input Power pin not driven by any output power pins
« Reply #5 on: February 26, 2023, 04:35:59 am »
If I remove the 330ohm resistor from the anode I no longer get errors, but why? Why does KiCad not like that I'm trying to limit the current to the LCD?

because the symbol was made to have the current limit resistor in the kathode and the anode connected to a supply

with the resistor the in anode the anode is not connected to a supply
 


Share me

Digg  Facebook  SlashDot  Delicious  Technorati  Twitter  Google  Yahoo
Smf