Led front panel

Hello,

Is it said in the manual that we can use a bicolor led to have the wake/sleep information by using the pins 2 and 4 from the front panel.
However with a bicolor led there are 3 pins, one for the green led, one for the yellow and last one for the ground.
Which pin has to be used to power the yellow led ?
I can't try it that's why I ask.

Thanks

 

There are two types of bicolor led. A 3 pin and a 2 pin version.
The Intel ATX front panel standard specifies a 2 pin version.

The voltage source can be from either of the two pins, with the two LEDs arranged so one will always be reverse biased in the circuit, and not produce light. A nice diagram is one the following page: http://www.instructables.com/id/The-RedGreen-LED-Guide/

 

Thanks for the explanation !
I can't find any cmos led with 2 pins, it would be to used them on an integrated circuit.

 

Here is the description of the power status pins on the front panel connector:

FP PWR_P/SLP_N: Power/Sleep messaging LED terminal 1 with 510Ω pull-up resistor to +5V_A voltage. Connect it to an extremity of a dual-color power LED for power ON/OF, sleep and message waiting signaling. Please refer to Intel® Front Panel I/O connectivity Design Guide, chapter 2.2.4, for LED functionalities and signal meaning.

FP PWR_N/SLP_P: Power/Sleep messaging LED terminal 2 with 510Ω pull-up resistor to +5V_A voltage. Connect it to the other extremity of the dual-color power LED above mentioned.​

This is the power status LED on the board: https://www.mouser.it/ProductDetail/Lite-On/LTST-C155GYKT
And you can view how it is wired in the schematics, page 22 (downloadable from https://www.udoo.org/docs-x86/Hardware_Reference/Resources.html).
A through hole type of the LED is: https://www.mouser.it/ProductDetail/Lite-On/LTL-14CDJN & https://www.mouser.it/ProductDetail/Lite-On/LTL-14CDJ (note: I performed a brief search for these two models, so do further research before using them in your project to ensure compatibility)

 

I found that using a 2pin "inverse parallel" LED did not work as per the description in the manual, and I had to fit a 3pin "common cathode" LED and borrow a ground signal from one of the I/O connector pins, with the two anode pins going to the front panel LED pins, that way with a red/green LED, the green alone is on when the board is on, and green and red are both on (giving a sort of amber) when the board is off ... HTH

 

Due to the interest in connecting an external LED for status information, I have set up a simple circuit to show expected results (though I used two LEDs instead of a bicolour LED. The voltage source switches correctly.

1. Board plugged in and in the power-off state
2. running state
3. sleeping state

 

IIRC the onboard orange/green LED is driven separately from the front panel LED, is there a BIOS setting that can affect this?
I purchased a 2pin LED expecting it to work as you showed, but mine certainly didn't work that way, I measured with a multimeter and had to buy a 3pin LED ...

 

You are correct, the front panel LED is operated by the STM32. Not sure why the 2pin LED you purchased did not work.
As far as I'm aware, there is no setting in the firmware to change the operation of the LED.

Do you have the latest firmware 1.03 on the board? https://www.udoo.org/docs-x86/Advanced_Topics/UEFI_update.html

 

Actually (due to working with Ettore on the HDMI-CEC driver) I have a pre-release 1.04 firmware, but I was running 1.03 when first fitting the LED ...

 

@andy-burns Ettore has just tested on his board with the pre-release 1.04 firmware, and it functioned as shown in the photos of my board.

Have you connected one wire to pin 2 and one to pin 4? (the green box in this linked picture: picture link)

 

Yes, certain I was using the correct pins, perhaps there's a fault with the pull-up resistors on my board?

I'll have more chance to look at it at the weekend, it is working satisfactorily for me with the 3-pin LED, but would be good to see why it doesn't work with the 2-pin LED as per the docs.

 

Thanks for all the details
What's the difference between the power-off state and sleeping state ?

If I use the same led that's already on the board the LTST-C155GYKT where should be the pin 2 and pin 4 ?

Best Regards,

 

Going by the manual (rather than my experiences)
pins 1 and 4 of the LED to pin 2 of the front panel connector
and pins 2 and 3 of the led to pin 4 of the connector

 

Microsoft have published a guide on the different power states: https://docs.microsoft.com/en-us/windows-hardware/drivers/kernel/system-sleeping-states